@lukesgoldies: The way I see it is that no matter how careful you are, you’re gonna get the water dirty when you clean your filters, and the best possible time to change your tank water is right after you get it dirty. Yes the water contains beneficial bacteria, but the amount is so minuscule that the difference between doing it the same day vs on different days is negligible. The water quality will be better because you removed more organic waste than the marginal increase in nitrogen cycle stability. This is just the way I see it, I may be wrong but it works on my tanks. #fish #goldfish #aquarium