Fish Tank Stocking Levels

The amount of fish you can fit into a certain tank is widely debated. There is a general rule: 1 inch of fish per gallon of tank space. This has been widely refuted and railed against, but has ultimately stood up. It is my opinion that this is a very good number in most cases. So: 

1 inch of fish per gallon is a good rule for beginners. it has some very important clauses to it though:

- The rule is for MOST fish. Many more advanced fish have specific territorial or swimming needs
- The rule decays as the fish gets largeer. It works best for fish 1 inch in length, so 10 1" fish in a 10 gallon adheres to the rule perfectly, but with fish like cichlids, only research on the species can tell you..
- 1 inch of fish per gallon should not bbe added to a brand new aquarium. The aquarium must "cycle," and adding too many fish will create too much waste before the tank can adjust to it. See cycling in Basic Fishkeeping.

During a debate on the Petfish.net Forum, We finally came to a conclusion about the validity of the rule. Was basically decided that what I stated above was all well and good, but with proper care "1 inch per gallon" could be far exceeded. The following factors effect the possible stocking levels:

• Waste Management - Fish naturally produce toxic chemicals in the water, and biofiltration must be adequate to remove it all. This means you must have a surface area in your tank large enough to accommodate a bacterial colony of the appropriate size. Filter floss, gravel, and bio-wheels create this surface area. You must also be willing to do enough water changes to eliminate nitrate, the end product of biofiltration.
• BOD - Stands for Biological Oxygen Demand, you must have enough oxygen entering the tank water for the fish to breathe. Plants, airstones, and water circulation improve this.
  

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