If water changes is going to be your only way of nutrient export and control, as well as chemically balancing your tank for a variety of coral, you may want to consider using a top quality salt. There are a few quality salts to choose from. I prefer Tropic Marin, however a lot of people are enjoying AquaVitro Salinity salt and that new salt from Seachem.... There's also Saltwater Correct - and it's made in America, 100% and all of the profit made from it goes towards aquaculture research. Anyways, the point is - if that's the only way you are going to control nutrient buildup, get a high quality salt.