Depends on the tank & filtration. My 125, with the grates under the sand and a mechanical filter.....never do it again. Bi-weekly water changes, drain the tank every 6 months or so and clean up the goop from under the grates (was pretty much a bi-product of meat eating fish) and pretty constant algae cleaning form setting the tank up across from a window. The 300 had two over flow boxes that were full of bio-balls to silence the water falling, a sump with bio balls (for bio filtration), a protein skimmer, uv filter and a mechanical paper filter. It was connected to the ro unit, so never had to top the tank off. Monthly I would pull out 30 bio balls from the sump and rotate them into the overflow boxes. The ones from the boxes would then go into the sump (was told this was not necessary but I did it any way. Would then stir up the bio balls in the sump, just to mix the "new" ones in. Monthly maintenance also included removing the filter cartridge and cleaning it, as well as taking the head of the skimmer outside and hosing it off. At the three month mark I would exchange 120 gallons of water (always had 3 40 gallon trash cans on wheels ready to go with the sg set at 1.018-1.020 just in case), the month after a water change I would also swap out the uv filters light. That was the extent of it. The water change did take a couple hours, the rest of it was closer to fifteen minutes. Would test the water weekly in the beginning, but after the first few months was more bi-weekly. I also was dealing with a great shop in regards to the fish. Kingsley was from Sri-Lanka and imprted almost all of his own fish. He had an import business, so he would just call his friends back home and they would go diving looking for what he needed. More on the specific gravity later, but one of the reasons I went with lace rock instead of live rock was the ability to run a lower specific gravity, with less salt in the water it allowed for more oxygen Kingsley also had a Marine Biologist degree, so he understood this stuff pretty well.
