Whatever size tank you have I advocate changing 2.5% weekly (in nanos divide that up daily). Frequent small water changes are better that infrequent large changes. Every tank is different and one needs to observe their own tank and act according to what they see. Water changes in my view are a inefficient method of nutrient export but they do replenish trace elements which is good. I believe the weekly changes will lead to more consistent availability of these elements. Large percentage water changes can be destabilizing to a reef tank.