I have 2 fx6’s running on a 90 gallon tank with one Black wolfish in it and yes I know that’s over kill I don’t know close to everything but I’ve had fish for 6 years now and know as much as I’ve been able to learn but I can’t figure out how to properly be chamgimg the filter media and pads without destroying the tanks biological system the monthly cleanings and one pad changes aren’t a problem but the every 6 month big change messes the whole thing up, I tried to stagger the changing making the media changes every 6 months and 3 months into that the pads are changes and so on so that each thing is still being changes every 6 months but still 3 months apart to try to preserve some of the healthy bacteria any help or ideas?