I’m trying to stick to weekly water changes. I won’t do one today because we did tie dye last night and it’s all over my hands. I will get one done sometime this week before we leave for a vacation next week though.
Last Sunday, but I usually change about 35g in my 120DT/40 sump about every 6 weeks or so. More often if something doesn't look right, and occasionally it will go 2+ months (life gets in the way sometimes!).
I do a 1 gallon water change every day on my 10 gallon LPS reef tank. My tank is only set up with lights, a heater, and an ATO so my water changes help replenish the elements consumed by the coral. I mix 50 gallons in a brute trashcan at a time so a water change only takes 5 minutes or less to complete