It seems to me that over the years one part of water changes is to find things that I have been missing. For example, today I did an H20 change on my 90. I added an Aquaclear 70 to the tank as it seemed like it needed more water flow. Detritus had been building up on the tank bottom which I attributed to the fish growing. Well I came to discover that my Emperor 400 was not running at all! This led to a mad dash to the pet store for new filter media. Got home and the filter wants to be loud now LOL! So the water change let to that and now the tank is way more clean in just a few hours. Happy fish I think.