If you have ever seen a vibrant saltwater tank or gone scuba diving in the ocean, you will know how beautiful the reef environment is with its fishes and corals. Most people want to recreate that beauty by setting up their reef tanks at home.

However, you cannot just randomly stock an aquarium with fishes and call it a day. There are a lot of steps that you have to take to maintain your saltwater aquarium.

A saltwater tank is an aquarium that keeps corals and marine life in an enclosed environment. This environment, however, needs to be correctly balanced so that it can retain the oceanic beauty.

The following article is a saltwater fish compatibility, stocking, and acclimation guide. More so, you will become aware of the factors to consider before buying fish, and how to limit the territorial aggression in your saltwater aquarium.

Reef Tank Stocking Guide

How Many Fish and Corals Should You Add: Reef Tank Stocking

It is not that difficult to determine the stocking levels of saltwater aquariums. One of the convenient methods, when it comes to large or small fishes, is to use the rule of thumb.

The rule of thumb will help you determine how many corals and fish are in your tank, theoretically, able to contain. You should keep in mind that the larger and smaller species of fish will occupy your tank in different ways.

For instance, the large species take up more space, have bigger appetites, and also produce more waste than the smaller species. Due to this, the rule of the thumb between large-bodied and small-bodied fish varies considerably.

For small to medium-sized fish, the rule of thumb is 2 inches of fish for 10 gallons of the tank capacity, and for medium, to large-sized fish, it is 1 inch of fish for 10 gallons of the tank capacity.


According to the rule of thumb mentioned above, you can, for instance, stock an 80-gallon tank with either 8 inches of large fish or 16 inches of small fish. However, there are other factors with which you can determine the stocking level other than the rule of thumb.

The number of fish that you choose can also be influenced by several factors such as

  • The efficiency of the filtration system
  • The age of your tank
  • Whether it is old or newly established
  • The number of corals that are in the aquarium

Also, the real volume of your tank after you have added the aquarium accessories like ornaments, sand, rocks, plants, and so on.

·      Fish Compatibility

When you are stocking your reef tank for the first time, the number of fishes and their sizes are the essential things to consider. Although these are not the only factors, you should think about it.

For the saltwater, fish compatibility factors such as habitat compatibility and behavioral compatibility need to take into stride.

·      Behavioral Compatibility

All types of fish are to lesser or greater degree predators. Moreover, any kind of fish, regardless of their species, will be aggressive or assertive when it becomes aware of the need to protect its mate, itself, or its territory.

Among the fishes, the Moray Eels and Lionfish are highly predatory. For this reason, these two have to be kept in a separate aquarium, away from the smaller fish. Otherwise, their natural hunting nature will cause desolation if placed under the same tank.

If you are introducing new fish at your already established aquarium, they too will receive the brunt of aggression from the settled marine community, no matter what type of fish it is or what species it belongs to.

However, these conflicts are regular, and after the territories have been established again, the fish will settle down. There are also a few steps that you can try to lessen aggression.

The first step is to give them space, a lot of space. Next, you can try diversity; for instance, an Angelfish might not be tempted to fight with a Clownfish. The last step is not to combine the smaller fish with the larger ones.

As all fishes are inherently predators, to some extent, it is better to prevent the little ones from becoming food for the large fishes.

·      Habitat Compatibility

There is more to compatibility than just learning to co-exist with other fishes peacefully. It is also linked to the harmony between fish concerning their lighting, habitat, and feeding requirements.

Even though fishes of two different species live in the same coral reef, they might belong to totally different oceans. So, the two species are likely to be acclimated to different water chemistry levels.

Furthermore, to make sure that the fishes thrive and get along in the aquarium, you need to shape the tank with the conditions that match the needs of your fish. And this is easier to do if all the fish in the tank have similar requirements.

Besides, if you decide to keep corals in your reef tank, make sure that there is harmony between the corals’ and fish’s requirements.

Compatibility with Corals (If You Want A Reef Tank)

Since corals are also living creatures, they too have some habitat and compatibility considerations. Here are some of the factors to take note of while you’re planning for a reef tank.

·      Compatibility

Before choosing corals, you need to check the compatibility among them and with the fish that you are planning to introduce. For instance, anemones are known to eat certain species of fish and shrimps, so you have to research on it beforehand.

·      Lighting System

The lighting is crucial for both corals and aquatic plants because of its photosynthesis process. Different type of corals requires a different sort of lighting system, so it needs to be thoroughly explored.

·      Space

Corals need sufficient space to grow and thrive. They tend to become aggressive if they think there is competition. For soft corals, you need to leave 3 inches of space, and for hard corals, you will have to leave a bright area of 6 inches.

Factors to Consider Before Buying a Fish

If you are buying fish for your saltwater tank for the first time, it might be a little disorienting. This is because you will find yourself surrounded by a dazzling array of different species of fish.

However, you have to proceed with caution because impulse buying the fish just because they are exotic looking and pretty is going to be a recipe for disaster. So while selecting the fish, you have to evaluate their health and care needs critically.

Instead of trying to see if the color of the fish will complement your furnishings, you should research on the behavior of each species. In other words, you have to do your homework before going to buy the fish.

·      Does the Fish Look Healthy?

While selecting the fish, you need to look for visible signs on the fish that indicate diseases. Their behavior could also mean any hidden ailment or illness. However, you cannot make a proper conclusion just by glancing at the fish.

You need to examine the specimen for a considerable amount of time before making a decision. The warning signs that could indicate an illness includes velvety patches or white spots, incomplete or torn fins, lesions, or necrotic ulcers.

In addition to that, missing scales, rapid breathing, cloudy eyes, shaking of the body, spasmodic swimming, grating against rocks or objects in the aquarium, brooding at the corner, listlessness, and puffing at the surface.

One thing to bear in mind is that you should not only keep a lookout for these signs in the specimen that you are buying. You should also make sure that the other fishes that are displayed with these don’t have the symptoms.

This is because if one fish in the tank is ill or infected, then it is safe to presume that other fishes have been affected as well even if they haven’t shown any symptoms yet.

·      Consider Its Adult Size

This is an essential point to consider because most people have made the unfortunate mistake of getting an adorable small fish without researching its growth capacity.

Frequently the diminutive fish grows into a gigantic, colossal size, which is simply too enormous to handle in a home-sized aquarium. Therefore, you have to make sure that the fish you buy doesn’t outgrow your reef tank.

·      Is the Fish Eating?

If the fish refuses to eat, it can be a symptom or a sign that it is overly stressed or ill. It might also be because of the fish not being able to recognize the food item as a good thing because it may not bear any similarity to the food it has eaten in nature.

So before buying the fish, you need to check if it has been eating properly. Some species of fish are extremely picky about their food and will only eat particular types of food, so you need to research on that before buying a specimen.

·      Captive Breed or Wild-Caught?

You can choose either of the two options, but the safer route is to select a captive-bred fish over wild-caught ones. Since the majority of freshwater fishes are brought up in captivity, it won’t be such a big issue.

But in the marine zone, most specimens of fishes are wild-caught. Only a few of the fish are captive bred. It’s important to know which one to choose because, generally, captive-bred fish have a high tolerance.

They are hardier than the wild-caught fish and can adjust more quickly. Even though they cost more, the captive-bred fish have a higher survival rate.

Introducing the Fish to Your Tank

Be mindful of the factors below before putting in any new fish in your tank.

·      Which Level of The Aquarium Does the Fish Prefer?

There are generally three categories in which most fish can be placed, and it is based on the water level they tend to inhabit. The levels are bottom dwellers, mid-water, and top-water.

Most of the time, you can hazard a guess of a fish’s water level by looking at the position of the mouth. The fish with an upturned mouth is indicated to be at the top-water level, while a forward-facing mouth suggests the fish is at the mid-water level.

Furthermore, the down-turned mouth of the fish indicates a bottom level dweller. It’s crucial to know this because an aquarium looks aesthetically pleasing if the fishes are evenly distributed throughout the water.

·      Consider the Water Chemistry of Your Fishes and Corals

The fishes that have been collected from the coral reef come from the most stable environment on the planet. They will thrive in the tank water, which as the same chemical makeup such as calcium level, pH, salinity, alkalinity, etc.

However, freshwater fishes have become evolved to adjust to the diverse mixture of ecological corners around the world. The captive-bred fishes will be able to adapt to a wide variety of water conditions.

How To Acclimate Your Fish Before Adding To The Tank

It is safe to presume that the quality of your reef tank’s water will be a bit different from the quality of the place from where you bought the fish. It can be stressful and deadly to fishes to experience changes in water, whether in pH, temperature, or salinity.

So after putting it through quarantine, you need to acclimate the fish to the water in the new environment. The process of acclimation is slow. First, you’ve to pour the fish and water gently out of the plastic bag and into a new plastic container.

Next, tie a few knots in the adjustable airline tubing. You should then place the first end of the tube in the display or quarantine tank and the other end in the acclimation bag.

Finally, start the water flowing by tightening or loosening the knots tied in the tube and adjust it to an even drip. Then when the volume of water in the acclimation bag is doubled, you can throw out half of the water and continue dripping.

Repeat this step until the water level in both your display tank and acclimation vessel are equal. You can then release the fish to its new home.

Final Words

We hope our saltwater fish compatibility, stocking, and acclimation guide gave you a general idea by now. Following the methods and ways mentioned above will help you to avoid common errors and accidents.

Your efforts to keep a healthy, vibrant, and beautiful community of fish will be possible if you be patient and diligent during the whole process.

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