They get cleaned like crazy every two weeks.. its the 35 gallon res that gets stinky as hell and it gets that way on day 2 after res change.. i think its the beneficials coming to life though.. which also means icsnay on the H2O2... but if I go aeroponic Im gunna love me up some h2o2.. cuz beneficials that live in grow media arent needed when you dont use grow media