Here’s a better understanding on WHY we do water changes:
Your filter picks up waste. (Uneaten food, poop, etc)
The live bacteria break down the waste and it becomes ammonia as it decays.
This broken down waste becomes nitrite.
This nitrite gets absorbed by a different kind of bacteria, then output as nitrate.
Ammonia, being the most toxic, nitrite still toxic, and nitrate is much more tolerable in small concentrations.
In a tank with a filter alone, the nitrate ends up adding up and eventually becoming toxic to your fish.
The water change dilutes the amount of nitrates with fresh water. Thus, making the nitrates less toxic since it’s now a lower concentration.
IF you wanted to do LESS water changes, you could add live plants to complete the nitrogen cycle and absorb all the nitrates.
Now on the topic of filtration:
Over filtration is better. Yes.
Oscars, very messy fish. They will REQUIRE over filtration. So your “over filtration” becomes standard filtration for your stock.
Your filter (canister) is only so efficient. That being said, even with the canister on a small tank, some waste stays inside the tank. (Stuck in the gravel, sand, decorations etc.) your water changes will help remove this waste that is decaying inside the tank, never having made it to the filter.
And canister filters are known as “nitrate factories” because while they hold tons of media, the increased bacteria can handle much more “cleaning”, and all this broken down organic material remains inside the barrel of the filter. Until it is removed from the tank AND filter, your tank still won’t be “clean”.
So bottom line here is this:
Your canister is decent for your tank and stock. It will need to be cleaned frequently.
You will also need to perform routine water changes.
It’s a necessary evil in the hobby.
For a “low maintenance system”, do some research on the “Walstad Method”.
