Stocking Levels
The problem with aquariums is that fish swim in their own toilet! So a small water volume is easily polluted. In a large aquarium, the water volume dilutes the ammonia the fish excrete so pollution takes longer. However, this difference means a statistical stocking level is difficult to quote for all size aquaria, hence contradictions in stocking level advice.
Additionally, adding a large fish, such as an Angel, is equal to adding 6 small fish such as Neons in terms of the excreta they produce. Small Goldfish become big Goldfish, because they double in size every year, and so double the excreta.
You need a good filtration system to remove the ammonia. Use a powered filter,
internal or external but still do lots of partial water changes to flush that loo!
About 10% weekly is OK. Certainly do not wait weeks or months and then do a massive
clean out, the fish have to live in ever-
The best way of checking stocking levels is not by numbers (the fish grow all the
while too) but by testing the water....the ammonia level must be zero at all times
and the nitrite level can be no more than a trace -
Do not overcrowd the tank, if you want many fish, get a big filter. Water quality is everything for fish. Get the water quality right and the fish will be happy and happy fish are healthy fish.
To check all this use a Nitrite (note: not Nitrate) test kit and stock until the first signs of a trace of nitrite (tested daily), this is the limit for your particular system.
Aquarists often complain that different books give differing levels for stocking the tropical fish tank. In fact these are not contradictory but reflect the values of the times when published.
In the 1960s the books stated: take the length and width in inches and multiply together to give square inches then divide by 10 to give inches of fish, minus tail. In those days, with no power filters, the often daily water changes allowed quite high stocking levels.
In the 1980s with the popularity of undergravel filters and a knowledge of biofiltration, the levels quoted were: take the surface area in square inches and divide by 13 for small fish (e.g. Guppies), by 18 for medium fish (e.g. Mollies) and 20 for larger fish (e.g. Firemouths).
In the 21st Century, technology allows you to stock to the limit of the individual aquarium with its own filtration system – use the nitrite tests to assess water quality. Some fish, particularly Goldfish, will grow rapidly and that small young fish will double in size (and so double the excreta) in just a few months.
This means a statistical stocking level is difficult to quote for all size aquaria, hence contradictions in stocking level advice. Test, to be sure....
