Biological Loading

How many fish can my aquarium hold?

Biological loading is a term you may remember from high school science. You probably did a field trip to a storm drain where you took some water samples for analysis.

This concept has practical meaning for aquarium keepers. Biological loading is a system for measuring an ecosystem's wastes and required resources in relation to how many inhabitants it can support. For the aquarium (an ecosystem) it determines the number of organisms that can be kept within the fish tank.

It is safe to say that the larger an aquarium is the more fish it can hold. As a general rule it is often said that an aquarium's fish capacity is equal to 7cm of fish per liter of water. In biological loading terms 7cm of fish per liter of water is the maximum loading the ecosystem can sustain. The aquarium stocked at this level would be said to have a high biological loading.

Unfortunately 7cm of fish per liter is not a good measure for determining fish capacity as it does not take into account the specific filtration method, water temperature, fish growth and other limiting factors. To accurately determine the precise maximum biological loading would be a complex process. An understanding of the principals of biological loading can help prevent and troubleshoot aquarium problems however.

The main things to consider are dissolved oxygen and dissolved Nitrogen componds. Doing the following things will increase your maximum biological loading, allowing you to safely keep more fish.

• Agitate the surface of the water. This is were the majority of oxygen will enter the water.
  
• Cooler water can hold more oxygen. Keeping the water at the bottom of your fish's preferred range will allow more oxygen to be available.
  
• Do water changes of at least 25% weekly to remove nitrate. Do not change to much or you may upset the useful bacteria.
  
• Activated carb
on and other chemical absorbing resins, granules and chips can increase the productivity of your filtration without increasing turbulence.
Clean up uneaten food scraps imm
• ediately. Sometimes less is more.

Also remember to consider the social needs of the individual species. Breeding fish, cold water fish and aggressive fish will all need more space. This can not be provided by a tank with maximum biological loading.