Caliban07
Aquarium Advice Addict
Another thing to keep in mind beyond the whole bit of stocking levels, differences in water coming in vs going out, etc, is if the tank is planted... If it is, what's your fert routine? Sometimes you can be totally fine on stocking levels and matching water coming in vs going out, but you still need to do 50% weekly water changes to level out the ferts that are going into the tank each day and avoid algae. PPS Pro is one of the dosing regimens that do this, but there are several others too.
Basically, trying to oversimplify water change schedules down to a rule like the 1" of fish per gallon stocking rule is doomed to be as inadequate as that same rule. You really do need to take a look at all the factors and adjust for each tank's situation.
I agree with your notion that we wouldn't go round quoting the 'inch per gallon rule' so why would we go round with a generic figure on how much water you need to change and how often?
Advice like 'your tank is an un flushed toilet and your fish are swimming in their own waste isn't very informative advice to me.
With the help of scientific understanding we can advise and allow someone to use the science, the facts, the results, visual awareness (agreed with Andy) and common sense to make there own informed decision on the needs of their individual tanks water change routine.
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