When Is A Tank Too Full?

[Warehouse]

Hi All, this is purely a hypothetical question, I am not intending on doing this but I am curious about it.
 
I have a 125 litre tank with an external filter that would easily run a tank 3 times that size. I have religiously stuck to the 1" per gallon rule with the fish, but there are a few snails and shrimps in there, and a couple of new panda cory's were born recently.
 
So I got thinking, how would you know if you were overstocked? Would the ammonia and nitrite start to rise as the filter struggled with the load, or would a really good filter mean you could overstock and keep things in check? Is the amount of fish in a tank based on the actual physical size of the tank, or the ability of the filter to keep the water good?
 
Basically I'm asking if the amount of fish should be based on the water capacity of the tank or the cleaning capacity of the filter?

 

[DreamertK]

I think actually the NO3/nitrates would be the ones rising very rapidly in the tank, and a tank with more water in it has more space to diffuse more individual molecules. That is if you put one drop of pure NO3 in a 5ml test tube the reading would be a lot higher than if you put a drop of NO3 in a 50liter tank and tested the water. So both the physical size of the tank and the filter's ability. The bacteria can double their population in a day if there's enough food for them, and usually filter media never runs out for the bacteria. I would also add in the owners time as a factor. Sure you can overstock the tank, but do you have enough time in the week to make multiple 50% WC to minimize the NO3 production?
 
I would rather understock a tank and have less of a margin for error than overstock a tank for my own entertainment. Just my personal preference.

 

[leighton_87]

In short both:

You need to give your fish enough room to swim and be comfortable - overcrowding will not only result in unhappy dish but also stresses fish which may get aggressive. Think of locking a group of humans together in a confined space - the more there are and they less space they share the more likely fights are.

Then from a filter point of view - yes a large filter with plenty of good bacteria would get rid of the the ammonia and nitrite but would convert it to nitrate and you would find nitrate builds up very quickly and you would need to do very frequent and large water changes.

Saying that with weekly 25%+ water changes and over filtering you can go over the 1 inch rule without too many problems.

Your nitrate build up will tell you when you water changes are often or large enough.