i typically do a 5 gallon water change once a month . about 65 total gallon volume. i recently did a ATI ICP test and i got a 3x 20% weekly change which i think its too much and im just doing 10% and twice a week . only to level out my parameters , my calcium and potassium were elevated nothing hurting . im ok with the water changes it takes about 30mins i spend about 1hour with water change and cleaning the glass. it is relaxing to me i have had periods of 3 months with no water change just adding elements. then ill do a icp test to make sure im in the range and make any corretions if i need to . my corals are doing great growing and im running out of space in the tank !