Saltwater Aquarium Information – How Many Fish Can I Keep in One Tank?

Salt water aquariums come in two basic varieties, those with live rock and those without. The type of ecosystem you develop has a large bearing on the number and size of fish and other marine creatures that you can house in a tank of a certain size.
In any event, a tank of a certain size can only hold so much plant and animal life. Having the right saltwater aquarium information and determining the limiting factors before making a decision as to what fish you want will make for a more balanced ecosystem and a less stressed and healthier tankful of marine creatures.

The Starter Tank

The most basic rule of thumb for stocking a fish tank is 1” of fish per gallon of water. This rule does work for a tank populated by small fish in a non live rock environment as is entirely appropriate for very basic marine tanks. For more elaborate tanks, the rule is so arbitrary as to be essentially useless.

Tanks with Crustaceans and Mollusks

For larger tanks with some crustaceans, mollusks and live rock, it is far safer to stay with 1’ of fish per three gallons of water. It may not seem like much but a 100 gallon tank will hold eleven 3” fish plus the other fauna in the tank.

A separate, significant consideration becomes the relative size of the fish to each other as Mother Nature has a way of eliminating the weak. Many marine species are highly predatory towards smaller fish. A salt water aquarist must spend the proper amount of time finding appropriately sized specimens to add to his tank. This warning applies to the non-fish creatures as well.

A great example is the Pterois. Also known as the Lionfish, they are notoriously rapacious in their appetites and can only be housed with other fish of comparable or larger sizes. This fact has had some very real world implication as detailed in this fascinating story – The Lionfish – The King of the Coral Reef.

Live Rock and Everything Else

It may not seem obvious but live rock takes up volume and thus decreases the amount of water available for the fish. With this fact in mind, you should decrease the amount of fish depending on how much live rock you add. The calculation is really rather simple. If the rock fits in a one gallon bucket, it displaces about ¾ gallons. So, for every ten pounds of live rock, reduce the amount of fishes by just two inches.

The Bottom Line

There are volumes of saltwater aquarium information available. So much that, if you tried to read it all, you would die before you ever enjoyed the beauty of a finished tank. Still, trial and error is a particularly expensive way to enjoy the hobby.

It is not necessary to start small in scope but have reasonable expectations of your abilities. It is not particularly difficult to keep small saltwater fish alive in a non-live tank. The difficulties, however, increase exponentially as you add exotic specimens and non-fish creatures.

Saltwater fish aquariums are a fascinating hobby and well worth the time and effort necessary to master the art.