you need to clean your canister filter out often, once a week, to remove the waste it collects! nitrate is the last stage of the biological cycle. nitrates are bad. they will collect in your filter’s media. it needs to be cleaned often! the beneficial bacteria lives on your rock, in your sand, on the glass, and everywhere. This bacteria is needed to break down fish pee (ammonia), uneaten food, fish waste. The more fish you have, the more food you will have, the more waste you will have, and the more bacteria you need in your aquarium. I didn’t want to spend more money on a sump and skimmer for a quarantine tank. This canister filter will work out great!