Rule Of Thumb For Population Level

[manwithnofish]

Since we have nothing to go on other than a "Rule of Thumb" regarding the number fish a given tank can support. And since we tend to push the limit by buying fish smaller than they will grow, and the fact that we would like to have as many fish as we can. What are the telling signs when we start approaching that limit. How do we know that it's time to reduce their numbers. What are the limiting factors from the fishes point of view? Can we identify the limiting quantity(s) and increase the carrying capacity by increasing the limiting quantity(s)? I know this is a multivariable issue with no simple answer, but how did anyone derive at the 1 inch / gallon rule?

This is a generic question, so please don't ask how many fish I have or how many gallons my tank is, or how large or what species, or anything specific about my tanks.

 

[Colin_T]

It comes down to filtration and water changes. You can have 200 fish in 50litres of water if the water is kept clean and the fish have room to move without touching each other.
If you monitor the water quality, particularly the PH and nitrate you will no when there are too many fish in the tank. If the PH drops rapidly it can indicate there is too much ammonia being produced. This can be from too much food or too many fish.
If the nitrates go up rapidly between water changes then there are too many fish in the tank or too much food going into it.
You can leave the tank as it is and just do more water changes and gravel cleans. Or you can reduce the number of fish in it, or reduce the food going into the tank.