Newbie questions, and some answers
There are lots of people asking the same kinds of questions on the reef forums, all questions I have asked myself. As I travel through the hobby I will try and compile some of my questions and answers.
What type of water should I use?
Never use tap water as it contains too many contaminants which can affect the wellbeing of your fish, inverts and corals. Always go for RO water. This can be made at home using using a multi stage RO unit or purchased from a local lfs if possible.
There are also lots of questions about which salt to use. Again there are many manufacturers and many different opinions. I decided to use the same salt as my lfs so that in case of emergency I could buy ready mixed salt water from them. I have recently added an RO unit and plumbed it in. Should have done this earlier as you know the quality of the water. LFS now producing RO with 0 TDS, better than mine. When looking at the amount of water I waste when producing RO I have now decided to buy from the LFS.
There are also lots of questions about which salt to use. Again there are many manufacturers and many different opinions. I decided to use the same salt as my lfs so that in case of emergency I could buy ready mixed salt water from them. I have recently added an RO unit and plumbed it in. Should have done this earlier as you know the quality of the water. LFS now producing RO with 0 TDS, better than mine. When looking at the amount of water I waste when producing RO I have now decided to buy from the LFS.
What do I use for testing?
Lots of questions regarding this subject. Lots of different products and ideas. Most people suggest a refractometer for measuring salinity but a hydrometer can also be used.
Most people on the forums suggest Salifert test kits for the basic testing and possibly an electronic probe for pH. A TDS meter can be very useful for testing the quality of your RO water.
There is a lot of info out there but try Testing your aquarium water for starters
I have started to use an electric probe for pH and a digital meter, the Hanna Checker for phosphorus. After about two years of regular testing I now very rarely test as I had found my water parameters were very stable. I know this will go against the grain for many but it works for me.
Most people on the forums suggest Salifert test kits for the basic testing and possibly an electronic probe for pH. A TDS meter can be very useful for testing the quality of your RO water.
There is a lot of info out there but try Testing your aquarium water for starters
I have started to use an electric probe for pH and a digital meter, the Hanna Checker for phosphorus. After about two years of regular testing I now very rarely test as I had found my water parameters were very stable. I know this will go against the grain for many but it works for me.
What type of lighting should I use?
This seems to be the biggie question. There is a wide choice depending on what you wish to keep, size of tank, setup, budget etc. T8 and T5 tube lights of various types and metal halides (MH) have been the traditional choices but newer LED lights are now coming onto the market. Many people on the forums have doubts over their effectiveness with sps corals in particular. More retailers are beginning to use them though. Advantages with LEDs are there very cool running, no problems with excess heat as with MH and also very cheap running costs. Can be expensive to buy.
I have chosen to use two Aquabeam 1000HD reefwhite tiles in my 36" aquarium. Am now considering a third tile but not sure. I have added an extra strip light and am delighted with the LED lighting. After 5 years there are many more LED lights available.
I have chosen to use two Aquabeam 1000HD reefwhite tiles in my 36" aquarium. Am now considering a third tile but not sure. I have added an extra strip light and am delighted with the LED lighting. After 5 years there are many more LED lights available.
Should I leave the aquarium open or use cover glass?
Opinions vary with this question like they do with many others. There are pros and cons to each approach. If you leave them on, you might not get adequate air and gas exchange and your tank could heat up, especially if you have metal halide lighting. This isn’t as much of a problem if you have a sump for air exchange. You also have to keep the glass very clean or your light won’t be able to penetrate.
If you remove your tops, the above problems are eradicated, but you will have more evaporation (don’t forget to do your top offs with fresh RO water, not salt!) and you take a chance of fish jumping out of your tank. The problem can be solved solve by using “egg crate”, or florescent light covers made up of hundreds of little squares. It stops most jumpers and allows for air exchange and light penetration.
The last concern about having an uncovered tank is that if you have MH lighting, a splash on the bulb can cause it to bust! So make sure your lights are protected, either by a cover or by being far enough from the water to be safe.
I have chosen to cover my tank as I have a hood fitted with Aquabeam LED tiles and want to keep wrasses which are notorious jumpers. I also did not want to have too much light escaping into the rest of the room.
If you remove your tops, the above problems are eradicated, but you will have more evaporation (don’t forget to do your top offs with fresh RO water, not salt!) and you take a chance of fish jumping out of your tank. The problem can be solved solve by using “egg crate”, or florescent light covers made up of hundreds of little squares. It stops most jumpers and allows for air exchange and light penetration.
The last concern about having an uncovered tank is that if you have MH lighting, a splash on the bulb can cause it to bust! So make sure your lights are protected, either by a cover or by being far enough from the water to be safe.
I have chosen to cover my tank as I have a hood fitted with Aquabeam LED tiles and want to keep wrasses which are notorious jumpers. I also did not want to have too much light escaping into the rest of the room.
How do I clean the glass?
For cleaning inside the aquarium a floating algae magnet is needed. Make sure it is a floating one otherwise you will be constantly fishing for it! A scaper for removing hard to get coraline algae is also useful. The outside also needs to be kept clean. Don't bother with a bought window cleaner just a fifty/fifty mix of white vinegar and water.
I use a Magi Clean and a credit card and the above mix in a spray gun. I also have to occasionally employ a good wall paper scraper to remove build ups of coralline algae.
I use a Magi Clean and a credit card and the above mix in a spray gun. I also have to occasionally employ a good wall paper scraper to remove build ups of coralline algae.
What is a sump?
A sump is a second container or aquarium, usually under the tank but sometimes in a basement or separate room, where you can hide all of your ugly equipment like skimmers, filters, heaters, and pumps. You can use a smaller tank as a sump. It is normally divided into different sections. Lots of articles etc can be found about sumps. For morte information about my sump click the link.
What is a refugium?
A refugium is a section or container separate from your tank, where you can:
1. grow pods without them being consumed by fish and they will slowly be sucked into your tank for a food source.
2. You can “plant” some macro algaes to help with nutrient export in your tank. Basicially this means that if some large plant-like algaes are using the excess nutrients in the tank, there are little or none left for algae to grow in your tank. Cheato seems to be a better bet than caulerpa as it does nor cause as many possible problems.
3. A light for the macroalgae is needed and can either be on 24/7 (with caulerpa) or at an opposite time from the display tank (reverse photosynthesis).
4. Can house a Deep Sand Bed (DSB).
The refugium can be a section within your sump. I have a refugium with a DSB and cheato in the centre section of my sump lit with an LED light using reverse photosynthesis.
1. grow pods without them being consumed by fish and they will slowly be sucked into your tank for a food source.
2. You can “plant” some macro algaes to help with nutrient export in your tank. Basicially this means that if some large plant-like algaes are using the excess nutrients in the tank, there are little or none left for algae to grow in your tank. Cheato seems to be a better bet than caulerpa as it does nor cause as many possible problems.
3. A light for the macroalgae is needed and can either be on 24/7 (with caulerpa) or at an opposite time from the display tank (reverse photosynthesis).
4. Can house a Deep Sand Bed (DSB).
The refugium can be a section within your sump. I have a refugium with a DSB and cheato in the centre section of my sump lit with an LED light using reverse photosynthesis.
How do I introduce inverts into the tank
Slow drip acclimatisation
With inverts it is essential that a slow and steady acclimatisation process is used. They can be very susseptable to changes in salinity. Snails in particular, I have been told can suffer internal damage if not introduced correctly. I have added all my lifestock, inverts, fish and corals using a slow drip method. I floated the bags in my sump, fastened with plastic clothes pegs so they couldn't sink and ran a syphon using airline from the main tank. I used a clamp to control water flow to a slow rate of drops (approx 1/sec). Over 2 hours 30mins added about 3 times the volume of water.
How to do a water change?
A simple question but one that we all have to have an answer for. Most people recommend a 10% change each week. Others do more some do them less frequently. I guess that might depend on your own aquarium and how stable everyhing is. I am looking along the 10% each week routine.
I mix 20 litres of RO water with my salt. The manufacturer gives you the ration, mine is 1KG of salt for 24.2 l of water. I mix in a brew bucket with a thermometer and small pump. The bucket is covered. It stays like this for 24 hours. I then test the salinity of my tank and this water and adjust if needed.
I syphon the waste water from my tank, picking up rubbish if I can and then syphon the new water into my sump. This gives it a chance to mix through the return pump.
I mix 20 litres of RO water with my salt. The manufacturer gives you the ration, mine is 1KG of salt for 24.2 l of water. I mix in a brew bucket with a thermometer and small pump. The bucket is covered. It stays like this for 24 hours. I then test the salinity of my tank and this water and adjust if needed.
I syphon the waste water from my tank, picking up rubbish if I can and then syphon the new water into my sump. This gives it a chance to mix through the return pump.
How do you stick corals in place in the tank?
The answer here depends on the coral to some extent. If it is a small coral and you want to attach to rock try using a super glue gel, something like Loctite perhaps.
If the coral is already attached to a small piece of rock then using milliput will be a lot better.
I have found using milliput very easy and no problems.
If the coral is already attached to a small piece of rock then using milliput will be a lot better.
I have found using milliput very easy and no problems.
What fish and how many can I keep?
I found this really good article on Tropical Fishkeeping.com, written by Marc.
"When it comes to marine aquariums one of the most frustrating things can be the conflicting advise given on the Internet, in books, at at the pet shop as to what fish will do well in a particular aquarium environment. It seems that everything is up for debate, from which fish mix well together, to what size tank a fish can live in, and even if a fish is compatible in a reef environment. Although I can not resolve all of these issues in a short article, nor am I an authority on the subject anyhow, I do think I can help you work through some of the more common issues that you will face in creating a stocking list for your aquarium.
The first question many people ask when setting up a marine tank is "How many fish?". My first response to such a question is that it depends on the exact fish you select. This has very little to do with size, and everything to do with BEHAVIOR. Understanding fish behavior inside the aquarium is the key to creating a list of fish that will get along together, and allows you to understand the correct order in which the fish should be added.
Aquariums under 6' in length.
Lets look at a few examples to help clear things up. One of the most common aquarium sizes for the new marine hobbyist is the 29 gallon tank. When thinking of a 29 gallon tank, think of the physical environment available for the fish. The tank is 30'' in length, which tells us a lot about the amount of swimming space and territory that will be available for the fish. Such a tank does allow for some advantages, such as the reef structure. A 29 gallon tank is large enough that you are able to build a nice reef, using dry rock and live rock. In small tanks such as this you will want to add MORE rock per gallon than larger tanks. Adding more rock (less water) will actually create MORE space for the fish to swim and call home, because of the BEHAVIOR of the fish you will be looking to keep in this tank. I would suggest than any tank under 6' in length should be very crowded with rock forming a massive reef structure (or "rock structure" if it is a fish only tank). Lets move on and look at some fish to explain this in more detail.
It is easy to eliminate fish that should not be considered for a 29 gallon tank environment. For example, you won't be able to keep fish which are open water swimmers, such as Tangs, Rabbitfish, and Butterflyfish. These fish occupy large areas of the reef in the ocean and will never adapt to such a small environment. In fact, many of these fish are rather peaceful in the proper tank size, but become extremely aggressive when kept in tanks of less than 6' in length. It should also be obvious that you will not be able to keep fish which grow large in size, such as Pufferfish, Triggers, Lionfish, Groupers, and Lunar Wrasse. When you start to eliminate fish that can not thrive in smaller tanks, it becomes easier to categorize fish that can be kept.
Looking at fish that are appropriate for a tank of under 4' in length, such as a 29 gallon tank, you will see that they all have one thing in common. These fish are rock dwelling species, meaning that they spend most of their day very close to the reef, never venturing far from the small nook that they call home, or swimming in and out of the rock structure that makes up the reef. Lets call this "Group A". Examples of these fish include Basslets, Pseudochromis, Gobies, and Jawfish. You could also consider fish that stay small in size and generally dart in and out of the reef area, or swim about feeding on the microfauna. These fish are active fish, but not open water fish, and as such do not require as large of an aquarium. Lets call these "Group B". Examples of these fish include Dwarf Angelfish of the Centropyge genus (which do well in pairs), Hawkfish, Firefish (best in pairs), Cardinalfish, Blennies, Chromis (best kept in pairs not schools), Anthias, Carpenter Wrasse, Fairy Wrasse, and Clownfish (pairs).
As you look at the list above, think about the physical design of your tank. The numbers of fish that you keep will depend on how much rock you have and how well designed your reef is. Fish need an area to consider home, especially smaller fish such as those we are looking at here, and their home needs to be well defined. Each fish needs a place to settle down at night to sleep, and it needs to feel protected in this physical environment. The more rock that makes up your reef, the easier it is for fish to define their territory, enabling you to keep more fish in these sized aquariums.
Hopefully at this point you are starting to realize that you can more easily keep large numbers of fish from group A than you can group B. Fish in group A are going to stay in a more confined area, rarely venturing more than a few inches from their home. With a large reef structure you can easily fit 4 or 5 of these types of fish in a tank under 4' in length. You will be able to judge this based on the BEHAVIOR the fish exhibit when you add them to the tank.
Looking at group B you should realize that these fish are going to be out in the open more, and as such much more visible to the other fish in the tank. Keeping larger numbers of these fish becomes more difficult. When adding these fish to the tank, you also need to consider adult size. That being said, we all hate generalities when it comes to stocking an aquarium, but without them you can't make many decisions on your own. For this reason I am going to provide you with some guidelines as we go along.
So, rule of thumb #1: For tanks under 6' in length the adult size of a fish times 10 should not exceed the length of the tank. Using this rule you are able to reduce compatability mistakes. For example, in a 29 gallon tank of 30'' in length, you should not purchase a fish with an adult size of greater than 3''. This allows you to properly select members of the Centropyge angelfish that will fit your tank. You can easily see that a Bicolor Angel is not a good fit for a 29 gallon aquarium. You should instead consider choosing between the Flame Angel, Pygmy Angel, Flameback Angel, and African Pygmy Angel. Each of these fish stay small and will thrive in this size aquarium.
There are other considerations that you will have to pick up on as you go along. For example, you may have noticed that Clownfish and Centropyge Angelfish do very well in pairs. Although this is true, you have to be very careful with mixing fish within the same genus into the same aquarium, unless they are the same species and are added at the same time. This leads us to rule of thumb #2: In an aquarium under 6' in length, do not add more than 1 member of the same genus to the aquarium, unless they are of the same species, compatible as a pair, and added at the same time.
The final consideration is space. Even the largest reef structure will be limited by the size of the aquarium, so let me give you one more concept to consider. Rule of thumb #3: For an aquarium under 6' in length, consider adding 2 members of group A for every 15 gallons of tank, and 1 species of Group B for every 15 gallons of tank. This means a 10 gallon tank would get 1 fish from Group A and one species from Group B. A 20 gallon gets 2 fish from Group A and 1 species from Group B. A 29 gallon gets 4 fish from Group A and 2 species from Group B. This should help to give you an idea of how these fish will behave in terms of territorial behavior and compatibility. Note, a "species" may consist of 2 fish of the same species. In other words, a 20 gallon tank could probably house 2 Flameback Angelfish successfully, along with 2 fish from Group A.
Using these guidelines, lets look at a possible stocking selection for a 29 gallon tank with a large reef structure. In this example you could add 4 fish from Group A and 2 species from Group B. As such, you might consider 1 BiColor Blenny, 1 Royal Gramma, 1 Diamond Goby, 1 Jawfish of choice, 1 Flame Hawkfish, and a pair of Flame Angelfish. {edit: It has been pointed out that a BiColor Blenny and Royal Gramma will often fight due to similar color patterns. I agree with this point, but rather than change the article, I thought I would add this comment as an indication of how complicated these situations can sometimes be. Similar color patterns also need to be avoided.} The above example gives a total of 7 fish in a 29 gallon tank, which is far greater than most people would ever consider. Yet the stocking list is very organized and has very little risk of failure. In this example if you wanted, you could eliminate the pair of Flame Angelfish and instead keep a pair of Ocellaris Clownfish. Or you might decide to keep 1 Flame Angel and 2 Ocellaris Clowns. There are choices to be made, but you do have choices and can have a great mixed community of fish.
Aquariums of 6' in length or greater.
When you begin to move to larger sized aquariums things start to change. The length of the tank allows for the rules above to begin to bend. If you have not read the section above, I highly suggest reading it first. Even if your tank is not under 6' in length, the ideas presented above should help you to understand fish behavior and make it easier for you to stock a larger aquarium successfully.
When looking at a 6' tank you begin to have almost all fish as possible choices in the aquarium. Granted, there are some fish that should never be kept in a home aquarium, such as the Unicorn Tang, Red Snapper, Panther Grouper, etc. These fish grow far to large for the typical home hobbyist, so unless you have an aquarium of nearly 1,000 gallons in size, you should not be considering such fish. But for the rest of us, we can be happy to know that most fish we see available at the LFS are going to fit comfortably inside our 6' tank.
An aquarium of 6' in length allows us to also consider Tangs, Large Angelfish, Pufferfish, Triggerfish, Rabbitfish, Lunar Wrasse, Lionfish, Butterflyfish, and Squirrelfish as possible fish selections. Lets call this Group C. The difficulty in stocking from Group C lies more in the stocking order, as opposed to the selection of fish. But before we discuss stocking order let us first modify the rules above for fish selections in these larger aquariums.
Rule of thumb #4: For tanks of 6' in length or more, the "length+width" of the tank should be 5 times the adult size of the fish AND the adult size of the fish should be LESS than the width of the aquarium.
This is a generous guideline, but it does begin to help you distinguish between what fish will fit comfortably into a 125 gallon tank as compared to a 180 gallon tank. For example, looking at a Naso Tang with an adult length of 18'', you can see that this is not a good fish choice for a 125 gallon tank. By the rule, the Naso would require 7.5 feet of total "length+width", which the 125 provides. However, the 125 gallon tank is only 18'' wide, which does not exceed the adult size of the Naso Tang. By the rule, you would need a 180 gallon tank to accommodate the Naso Tang.
Rule of thumb #5: When adding members of Group C of the same genus to the aquarium, add them at the same time. More often than not this will work to prevent you from making a compatibility mistakes. Members of Groups A & B discussed above will generally not have to be added at the same time, primarily because of the added space you have available when dealing with tanks of 6' in length or greater.
Rule of thumb #6: For aquariums of 6' in length or more, you can add 1 unit of fish per 10 gallons of tank size. A unit is defined as 2 members of Group A or 1 species of Group B, with each fish from Group C counting as 2 units. For the purpose of tanks 6' and larger, include Chromis, Damsels, Dragonettes, and the Six Line Wrasse to be included in Group B.
So, lets look at an example. Lets say you have a 125 gallon tank. Your stocking list allows for 12 units of fish. Lets say you begin by adding 2 Percula Clowns (GpB), 2 Flame Angels (GpB), and 1 Coral Beauty Angel (GpB). This is 3 units. You have room for 9 more units of fish. You then add 1 Mandarine Goby (GpB), 1 Diamond Watchman Goby (GpA), 1 Royal Gramma (GpA), and 1 Sailfin Blenny (GpB). This is an additional 3 units. You have room for 6 more units, so you add 1 Yellow Tang and 1 Sailfin Tang to the tank at the same time, both being from the Zebrasoma Genus you don't want to break Rule #5! You still have room for 2 more units of fish!
{note added: I should make it clear here that this rule if meant to apply to a mixed community. You will have to use a bit of common sense based on adult fish size, especially if you venture into Large Angels, the Naso genus of Tangs, and Triggerfish. In fact, you may want to consider each of these fish to account for 3 units each!}
You can see how applying these rules of thumb allows you much greater flexibility in stocking your tank. It is very important to realize that this discussion has nothing to do with BIOLOAD. It has everything to do with fish behavior, aggression, and compatibility. I know what somebody is going to say, and I agree. This is not a perfect system. But it is a system that is far more effective than just putting random lists together and then asking some guy or gal at the LFS if you can have a given fish. It also allows you to post intelligent threads in the forum pertaining to stocking of an aquarium. There are other factors at play, such as fish aggression, but for the most part this method works well.
Stocking Order
As I mentioned before, the difficulty in stocking an aquarium is often in determining the order in which to add fish. Suffice to say, a Yellow Tang and a Flame Angel are compatible in a 125 gallon tank. However, it would be wise to add the Flame Angel first to improve your chances of success. These are things you just kind of learn after a number of years in this hobby. To make this easier, I will try to give you some guidelines on stocking order. There is nothing fancy here, just some generalities that I have picked up on over the years that you may find helpful. I will just list them out below.
1) It is best to add fish to the tank in Group order. In other words, Group A should be placed in a tank before Group B, and so on.
Exception: When adding angelfish, it should not matter which genus is added first to the tank. You can have a Large Angel in the tank before a Dwarf Angel, or visa versa.
2) When putting multiple species of Tangs in the same aquarium, add them according to genus. Ctenochaetus should be added first, followed by Acanthurus (Paracanthurs), and then Zebrasoma. Rabbitfish should be treated as Acanthurus Tangs for the purpose of stocking order.
3) Triggerfish and Large Angelfsh are best as the last addition to a tank. They become very territorial when established and may kill all future additions.
Exception: The Majestic Angel is generally peaceful fish, as are Angelfish of the Genicanthus genus. These can be added prior to other fish without causing harm to future additions. The Niger Trigger is also a frequent exception.
4) When making exceptions to these guidelines, consider diet. Algae grazers will rarely show any concern when adding a predator to the tank, and visa versa.
5) Fish with similar diets and similar color should be added at the same time, regardless of the rules. For example, a Lemon Peel Angel and Yellow Tang should only be kept in the same aquarium if added simultaneously.
6) Large Angelfish with near identical juvenile color patterns should not be placed in the same tank together. For example, the Majestic Angel and Blue Ring Angel are not good tankmates.
I could probably go on and on with these sort of guidelines, but I think these are the most common issues we face as aquarists when creating a stocking order or looking to add a new fish to an established tank.
You may have noticed that I nearly skipped the discussion of a 75-90 gallon tank. I did this very intentionally, as these tanks are very difficult to predict. You could include almost any tank of similar dimensions in this conversation, such as extra high tanks and similar gallon bowfront tanks. These are large enough that stocking from Groups A & B is very predictable. However, with the right mix of fish you can sometimes move into Group C. You can apply Rule #4 to a 75 gallon tank and often be successful, but it takes an experienced hand. For example, a Ctenochaetus Tang will generally work ok in a 75 or 90 gallon tank. You will notice that this genus of Tang is very passive compared to the others of the family, which is why it often works. If you do bend the rules for these tank sizes, pay very careful attention to the rules above concerning stocking order, as you will very rarely get away with any mistakes in a 4' tank
"When it comes to marine aquariums one of the most frustrating things can be the conflicting advise given on the Internet, in books, at at the pet shop as to what fish will do well in a particular aquarium environment. It seems that everything is up for debate, from which fish mix well together, to what size tank a fish can live in, and even if a fish is compatible in a reef environment. Although I can not resolve all of these issues in a short article, nor am I an authority on the subject anyhow, I do think I can help you work through some of the more common issues that you will face in creating a stocking list for your aquarium.
The first question many people ask when setting up a marine tank is "How many fish?". My first response to such a question is that it depends on the exact fish you select. This has very little to do with size, and everything to do with BEHAVIOR. Understanding fish behavior inside the aquarium is the key to creating a list of fish that will get along together, and allows you to understand the correct order in which the fish should be added.
Aquariums under 6' in length.
Lets look at a few examples to help clear things up. One of the most common aquarium sizes for the new marine hobbyist is the 29 gallon tank. When thinking of a 29 gallon tank, think of the physical environment available for the fish. The tank is 30'' in length, which tells us a lot about the amount of swimming space and territory that will be available for the fish. Such a tank does allow for some advantages, such as the reef structure. A 29 gallon tank is large enough that you are able to build a nice reef, using dry rock and live rock. In small tanks such as this you will want to add MORE rock per gallon than larger tanks. Adding more rock (less water) will actually create MORE space for the fish to swim and call home, because of the BEHAVIOR of the fish you will be looking to keep in this tank. I would suggest than any tank under 6' in length should be very crowded with rock forming a massive reef structure (or "rock structure" if it is a fish only tank). Lets move on and look at some fish to explain this in more detail.
It is easy to eliminate fish that should not be considered for a 29 gallon tank environment. For example, you won't be able to keep fish which are open water swimmers, such as Tangs, Rabbitfish, and Butterflyfish. These fish occupy large areas of the reef in the ocean and will never adapt to such a small environment. In fact, many of these fish are rather peaceful in the proper tank size, but become extremely aggressive when kept in tanks of less than 6' in length. It should also be obvious that you will not be able to keep fish which grow large in size, such as Pufferfish, Triggers, Lionfish, Groupers, and Lunar Wrasse. When you start to eliminate fish that can not thrive in smaller tanks, it becomes easier to categorize fish that can be kept.
Looking at fish that are appropriate for a tank of under 4' in length, such as a 29 gallon tank, you will see that they all have one thing in common. These fish are rock dwelling species, meaning that they spend most of their day very close to the reef, never venturing far from the small nook that they call home, or swimming in and out of the rock structure that makes up the reef. Lets call this "Group A". Examples of these fish include Basslets, Pseudochromis, Gobies, and Jawfish. You could also consider fish that stay small in size and generally dart in and out of the reef area, or swim about feeding on the microfauna. These fish are active fish, but not open water fish, and as such do not require as large of an aquarium. Lets call these "Group B". Examples of these fish include Dwarf Angelfish of the Centropyge genus (which do well in pairs), Hawkfish, Firefish (best in pairs), Cardinalfish, Blennies, Chromis (best kept in pairs not schools), Anthias, Carpenter Wrasse, Fairy Wrasse, and Clownfish (pairs).
As you look at the list above, think about the physical design of your tank. The numbers of fish that you keep will depend on how much rock you have and how well designed your reef is. Fish need an area to consider home, especially smaller fish such as those we are looking at here, and their home needs to be well defined. Each fish needs a place to settle down at night to sleep, and it needs to feel protected in this physical environment. The more rock that makes up your reef, the easier it is for fish to define their territory, enabling you to keep more fish in these sized aquariums.
Hopefully at this point you are starting to realize that you can more easily keep large numbers of fish from group A than you can group B. Fish in group A are going to stay in a more confined area, rarely venturing more than a few inches from their home. With a large reef structure you can easily fit 4 or 5 of these types of fish in a tank under 4' in length. You will be able to judge this based on the BEHAVIOR the fish exhibit when you add them to the tank.
Looking at group B you should realize that these fish are going to be out in the open more, and as such much more visible to the other fish in the tank. Keeping larger numbers of these fish becomes more difficult. When adding these fish to the tank, you also need to consider adult size. That being said, we all hate generalities when it comes to stocking an aquarium, but without them you can't make many decisions on your own. For this reason I am going to provide you with some guidelines as we go along.
So, rule of thumb #1: For tanks under 6' in length the adult size of a fish times 10 should not exceed the length of the tank. Using this rule you are able to reduce compatability mistakes. For example, in a 29 gallon tank of 30'' in length, you should not purchase a fish with an adult size of greater than 3''. This allows you to properly select members of the Centropyge angelfish that will fit your tank. You can easily see that a Bicolor Angel is not a good fit for a 29 gallon aquarium. You should instead consider choosing between the Flame Angel, Pygmy Angel, Flameback Angel, and African Pygmy Angel. Each of these fish stay small and will thrive in this size aquarium.
There are other considerations that you will have to pick up on as you go along. For example, you may have noticed that Clownfish and Centropyge Angelfish do very well in pairs. Although this is true, you have to be very careful with mixing fish within the same genus into the same aquarium, unless they are the same species and are added at the same time. This leads us to rule of thumb #2: In an aquarium under 6' in length, do not add more than 1 member of the same genus to the aquarium, unless they are of the same species, compatible as a pair, and added at the same time.
The final consideration is space. Even the largest reef structure will be limited by the size of the aquarium, so let me give you one more concept to consider. Rule of thumb #3: For an aquarium under 6' in length, consider adding 2 members of group A for every 15 gallons of tank, and 1 species of Group B for every 15 gallons of tank. This means a 10 gallon tank would get 1 fish from Group A and one species from Group B. A 20 gallon gets 2 fish from Group A and 1 species from Group B. A 29 gallon gets 4 fish from Group A and 2 species from Group B. This should help to give you an idea of how these fish will behave in terms of territorial behavior and compatibility. Note, a "species" may consist of 2 fish of the same species. In other words, a 20 gallon tank could probably house 2 Flameback Angelfish successfully, along with 2 fish from Group A.
Using these guidelines, lets look at a possible stocking selection for a 29 gallon tank with a large reef structure. In this example you could add 4 fish from Group A and 2 species from Group B. As such, you might consider 1 BiColor Blenny, 1 Royal Gramma, 1 Diamond Goby, 1 Jawfish of choice, 1 Flame Hawkfish, and a pair of Flame Angelfish. {edit: It has been pointed out that a BiColor Blenny and Royal Gramma will often fight due to similar color patterns. I agree with this point, but rather than change the article, I thought I would add this comment as an indication of how complicated these situations can sometimes be. Similar color patterns also need to be avoided.} The above example gives a total of 7 fish in a 29 gallon tank, which is far greater than most people would ever consider. Yet the stocking list is very organized and has very little risk of failure. In this example if you wanted, you could eliminate the pair of Flame Angelfish and instead keep a pair of Ocellaris Clownfish. Or you might decide to keep 1 Flame Angel and 2 Ocellaris Clowns. There are choices to be made, but you do have choices and can have a great mixed community of fish.
Aquariums of 6' in length or greater.
When you begin to move to larger sized aquariums things start to change. The length of the tank allows for the rules above to begin to bend. If you have not read the section above, I highly suggest reading it first. Even if your tank is not under 6' in length, the ideas presented above should help you to understand fish behavior and make it easier for you to stock a larger aquarium successfully.
When looking at a 6' tank you begin to have almost all fish as possible choices in the aquarium. Granted, there are some fish that should never be kept in a home aquarium, such as the Unicorn Tang, Red Snapper, Panther Grouper, etc. These fish grow far to large for the typical home hobbyist, so unless you have an aquarium of nearly 1,000 gallons in size, you should not be considering such fish. But for the rest of us, we can be happy to know that most fish we see available at the LFS are going to fit comfortably inside our 6' tank.
An aquarium of 6' in length allows us to also consider Tangs, Large Angelfish, Pufferfish, Triggerfish, Rabbitfish, Lunar Wrasse, Lionfish, Butterflyfish, and Squirrelfish as possible fish selections. Lets call this Group C. The difficulty in stocking from Group C lies more in the stocking order, as opposed to the selection of fish. But before we discuss stocking order let us first modify the rules above for fish selections in these larger aquariums.
Rule of thumb #4: For tanks of 6' in length or more, the "length+width" of the tank should be 5 times the adult size of the fish AND the adult size of the fish should be LESS than the width of the aquarium.
This is a generous guideline, but it does begin to help you distinguish between what fish will fit comfortably into a 125 gallon tank as compared to a 180 gallon tank. For example, looking at a Naso Tang with an adult length of 18'', you can see that this is not a good fish choice for a 125 gallon tank. By the rule, the Naso would require 7.5 feet of total "length+width", which the 125 provides. However, the 125 gallon tank is only 18'' wide, which does not exceed the adult size of the Naso Tang. By the rule, you would need a 180 gallon tank to accommodate the Naso Tang.
Rule of thumb #5: When adding members of Group C of the same genus to the aquarium, add them at the same time. More often than not this will work to prevent you from making a compatibility mistakes. Members of Groups A & B discussed above will generally not have to be added at the same time, primarily because of the added space you have available when dealing with tanks of 6' in length or greater.
Rule of thumb #6: For aquariums of 6' in length or more, you can add 1 unit of fish per 10 gallons of tank size. A unit is defined as 2 members of Group A or 1 species of Group B, with each fish from Group C counting as 2 units. For the purpose of tanks 6' and larger, include Chromis, Damsels, Dragonettes, and the Six Line Wrasse to be included in Group B.
So, lets look at an example. Lets say you have a 125 gallon tank. Your stocking list allows for 12 units of fish. Lets say you begin by adding 2 Percula Clowns (GpB), 2 Flame Angels (GpB), and 1 Coral Beauty Angel (GpB). This is 3 units. You have room for 9 more units of fish. You then add 1 Mandarine Goby (GpB), 1 Diamond Watchman Goby (GpA), 1 Royal Gramma (GpA), and 1 Sailfin Blenny (GpB). This is an additional 3 units. You have room for 6 more units, so you add 1 Yellow Tang and 1 Sailfin Tang to the tank at the same time, both being from the Zebrasoma Genus you don't want to break Rule #5! You still have room for 2 more units of fish!
{note added: I should make it clear here that this rule if meant to apply to a mixed community. You will have to use a bit of common sense based on adult fish size, especially if you venture into Large Angels, the Naso genus of Tangs, and Triggerfish. In fact, you may want to consider each of these fish to account for 3 units each!}
You can see how applying these rules of thumb allows you much greater flexibility in stocking your tank. It is very important to realize that this discussion has nothing to do with BIOLOAD. It has everything to do with fish behavior, aggression, and compatibility. I know what somebody is going to say, and I agree. This is not a perfect system. But it is a system that is far more effective than just putting random lists together and then asking some guy or gal at the LFS if you can have a given fish. It also allows you to post intelligent threads in the forum pertaining to stocking of an aquarium. There are other factors at play, such as fish aggression, but for the most part this method works well.
Stocking Order
As I mentioned before, the difficulty in stocking an aquarium is often in determining the order in which to add fish. Suffice to say, a Yellow Tang and a Flame Angel are compatible in a 125 gallon tank. However, it would be wise to add the Flame Angel first to improve your chances of success. These are things you just kind of learn after a number of years in this hobby. To make this easier, I will try to give you some guidelines on stocking order. There is nothing fancy here, just some generalities that I have picked up on over the years that you may find helpful. I will just list them out below.
1) It is best to add fish to the tank in Group order. In other words, Group A should be placed in a tank before Group B, and so on.
Exception: When adding angelfish, it should not matter which genus is added first to the tank. You can have a Large Angel in the tank before a Dwarf Angel, or visa versa.
2) When putting multiple species of Tangs in the same aquarium, add them according to genus. Ctenochaetus should be added first, followed by Acanthurus (Paracanthurs), and then Zebrasoma. Rabbitfish should be treated as Acanthurus Tangs for the purpose of stocking order.
3) Triggerfish and Large Angelfsh are best as the last addition to a tank. They become very territorial when established and may kill all future additions.
Exception: The Majestic Angel is generally peaceful fish, as are Angelfish of the Genicanthus genus. These can be added prior to other fish without causing harm to future additions. The Niger Trigger is also a frequent exception.
4) When making exceptions to these guidelines, consider diet. Algae grazers will rarely show any concern when adding a predator to the tank, and visa versa.
5) Fish with similar diets and similar color should be added at the same time, regardless of the rules. For example, a Lemon Peel Angel and Yellow Tang should only be kept in the same aquarium if added simultaneously.
6) Large Angelfish with near identical juvenile color patterns should not be placed in the same tank together. For example, the Majestic Angel and Blue Ring Angel are not good tankmates.
I could probably go on and on with these sort of guidelines, but I think these are the most common issues we face as aquarists when creating a stocking order or looking to add a new fish to an established tank.
You may have noticed that I nearly skipped the discussion of a 75-90 gallon tank. I did this very intentionally, as these tanks are very difficult to predict. You could include almost any tank of similar dimensions in this conversation, such as extra high tanks and similar gallon bowfront tanks. These are large enough that stocking from Groups A & B is very predictable. However, with the right mix of fish you can sometimes move into Group C. You can apply Rule #4 to a 75 gallon tank and often be successful, but it takes an experienced hand. For example, a Ctenochaetus Tang will generally work ok in a 75 or 90 gallon tank. You will notice that this genus of Tang is very passive compared to the others of the family, which is why it often works. If you do bend the rules for these tank sizes, pay very careful attention to the rules above concerning stocking order, as you will very rarely get away with any mistakes in a 4' tank