never......I used to do water changes (since I have no skimmer or "filter" on the 20gal....just ~20lbs of live rock and ~35-40lbs of live sand) but have since noticed that everything seems to be very happy with the higher nutriant levels (feather dusters, macros, etc.) and neither the zoanthids nor even the anemone seem to mind the setup (the nitrate levels are 0).....so why bother......I'll be setting up a 110gal (~180gal total system volume) soon that will have a skimmer but will still rely mostly on live rock, sand, and macros (will have probubly 150lbs of live rock and 200lbs of sand in the total system).....