I have two small 29 gallon tanks. I have found that 2.5 gallon water changes weekly or bi-weekly of 5 gallons has been the only way I have kept great tanks. I check the ph and nitrates weekly and feed less. I check phosphate and hardness a couple of times a month. My tanks are doing well, but if I skip the water changes I get in trouble. I probably should check calcium too, but never have found a test kit in the only store here that sells them.