How often do you clean your canister filter?

actually I haven't cleaned the canister filter - all sponge material etc. has been removed, only the ceramic balls are inside.

IMO i would do five 20% changes every other day that would give your
setup a good flushing

Yup, I agree do two consecutive 20% water changes a week for the next month or until nitrates are in check, reduce the amount of food if it's crazy amounts, and I would also suggest getting yourself a phosban reactor and use some bio-pellets. I had very high nitrates then I put a bio pellet reactor on with the CORRECT sized pump for bio pellets and they went from 50-5ppm over 2 months. I now never have nitrates over 2ppm. Good luck.

if done carefully (similar parameters as Aquattro suggested) a larger water change (50-80%) should go just fine. This is how I have done tank transfers in the past. Fill new tank 20% with old tank water then the rest with new water. As others have said, you don't want to be doing this on a frequent basis, but for a one or two off event for quick and short term correction purposes larger water changes are fine. A few weeks ago I did two consecutive 50% water changes in my tank to help flush out a treatment that I did on my tank.

The Ceramic balls might be the cause of your nitrates... If you have room in your sump, you might want to consider sourcing a zeovit reactor, use the zeo media and go on the base system (Start, Bak, Food). It's a fairly proven system and well supported.

Not sure what the concern is on water changes. Where does this common 20% come from? Not sure how too much clean water is going to hurt your fish, given that the important parameters match.

I appreciate your guy's input on this topic - lots already!

I understand the worry people have with such a large water change, and I agree it should be avoided as best as possible. I can't say that I've done one, and most people probably cant (even those who advocate not to do one) - because it gets into an uncomfortable zone.

But one analogy I heard from someone that was successful:

consider yourself as the fish - trapped in a garage with a car running, filling up with exhaust (Phosphate levels) - opening up the garage door to let everyone out as fast as possible may shock you, but is going clean the air and.

simply - each has its benefit and each has its downfall.

that's reassuring to hear - just picking up my bio pellet reactor from the post office today actually.

I threw 20% out there because It's what I've had experience with. Personally if it came down to it and fish were dying, I'd do as large of a water change as fast as possible. But I don't want to be responsible for crashing someones tank with inexperienced recommendations. :mrgreen: