Aquarium Stocking Guide - Things to Consider

Aquarium Stocking Guide - Things to Consider

Stocking an aquarium is one of the most asked question in this hobby.

To start I want to clear something up: the one inch per gallon rule. The rule states "for every inch of fish, you add a gallon of water". For example, a betta is 3 inches which means it can be in a 3 gallon tank. This also means an adult oscar (10-13in) is suitable for a 10 gallon. Or an angelfish in a 6 gallon. This is definitely not true and why this rule is a big myth. There just can't be 1 rule to determine how to stock your tank because there are so many types of fish and keeping fish just isn't that simple. As you read you will see how each topic will add up to the other.

The five things that you need to look at when stocking an aquarium are:
1. The size: Bigger is always better
2. The bioload: The less fish, the less maintenance
3. The aggressiveness: Give each fish its territory
4. Activity amount: Active fish need more space
5. Water Parameters: The water parameter need to be good for ALL the fish in the tank

The Size:
When setting up an aquarium, your goal is to create the best living space and ecosystem possible for your fish. The size of the fish really matters. You can't put an adult Arowana in a 10 gallon because it will not have enough swimming space. Would you like to live in your closet your whole life? Of course not! You would want something bigger and the bigger the better it is for you. This is the same concept with the fish, a bigger aquarium is always better. A betta is suitable in a 3 gallon, but a 5 gallon is much better. This is the same for all the fish.

The bioload:
The bioload is the amount of waste your fish produce. Plecotosmus, Livebearers, and goldfish are examples of fish with high bioload (poop a lot). The first topic says you can add 2 Goldfish in a 30 gallon, but because goldfish have such high bioloads, the tank will need a lot of water changes. If you add 2 goldfish in a 40 gallon, the tank will be much less maintenance. Plants can help lower that amount.

The aggressiveness:
Aggressive fish are almost always territorial which means they need space to have their own territories. You can add 2 male bettas to a 10 gallon tank according to the first 2 rules, but because of their behavior, you can't. Bettas will instinctively think that the other betta is trying to take its territory and WILL fight (or even kill) the other betta. Some people can manage to do a female betta sororities tank, but that is for another discussion. Some other aggressive fish are gouramis, sharks, CAE, Flowerhorns, Cichlids, etc.

Activity amount:
Finally the activity amount. Some fish are more active than others and therefore need more space. For example, a rainbow shark can be in a 29 gallon alone, but it will not thrive because the dimensions of a typical 29 gallon isn't enough room for the rainbow shark to swim.

Water Parameters:
The fish will be in the same tank which means the water parameters need to be good for all the fish in the tank. You can't add a German blue ram with a White Cloud Mountain Minnow because they aren't temperature compatible. Also, some fish come from alkaline environments while others prefer slightly acidic water. Or some are most comfortable in tanks with ample water circulation while others prefer still water.

I've had some help from:
86 ssinit, GelnnO, mattgirl, richiep, Mudminnow, and Nessaf


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Well written!
  • AIvinn
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This is one of the most useful things I've read for stocking on Fishlore. It will definitely clear a ton of confusion for people VERY new to the hobby.

Your grammar in this article was very on-point and everything flowed. Thanks for writing this up and good job. =)
Thank you! You made my day :)
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