How Often Should I Change Water in a Reef Tank?

Weekly water changes of 10% to 20% are a solid default for many home reef tanks. Changes export nitrate and phosphate, replenish trace elements, and reset dissolved organics when skimmers or filters lag.

Mix new saltwater to the same salinity and temperature as the display. Never pour undissolved salt slurry into the tank. Turn off pumps briefly if needed so sand is not blasted into corals.

Heavy feeding, large fish, or SPS-dominated tanks may need larger or twice-weekly changes. Light bioload nano tanks sometimes run 15% every two weeks — but test nitrate to confirm. Schedule changes in ReefDiary and note volume; consistency matters more than hitting an exact percentage every time.