I have two 420 gallon tanks that I change 75% of water every week plus I have a drip system that changes 200 gallons every day and use pond prime every day to treat new water.I have a bead filter on each tank,plus vacuum tanks every two weeks. I think one its very important to get rid of the organic waste as well as the water changes,because the organic material is what really effects water quality.If your not using pond prime I suggest you look into it its more concentrated than regular prime and will save you money.