why is it that you can't add too many fish at one time?

Question

what if the tank is already cycled?

Answer 1

Cycling the tank means you have the bacteria in the tank to start removing the ammonia by converting it to nitrite and nitrite. But each bacterium can only convert so much in a given amount of time. Each fish you add produces ammonia (as do snails, shrimp, crayfish, and uneaten food). Just because you have enough bacteria to convert the ammonia from one or two fish, doesn't mean they can handle an entire school before the ammonia accumulates to a toxic level. If you add fish gradually, the amount of bacteria will multiply because they have more food (ammonia), but only to a point. After you have more ammonia being produced than living space for your bacteria (substrate and filter pads), you develop permanent water quality problems (called overstocking your tank!).

Answer 2

The fish may be carrying different parasites and bacteria, so even if the tank has been cycled you would still be adding foreign elements.

The fish have to acclimatise to these new organisms and too many at one time would be too much too handle.

Also it's a good idea to let the fish get used to each other gradually.

Answer 3

if you add to many fish at one time, the amount of waste they create will be too much for your nitrifieng bacteria to handle and your water will become cloudy, but this is only before your tank is cycled

Answer 4

still, your bactria may not be used to so much waste at one time. its like waking up a weightlifter
in the middle of a holiday to weight lift 130kg.