I'm with Randy. I think constant water changes are much easier on the tanks inhabitants and better overall. I switched to automated daily water changes about 6 years ago. In that time, the health of my tank improved greatly and I use less water now too. On a 650g system (480g display) with over 60 heavily fed fish (many of which are large tangs), I change out 5 gallons a day. I keep 100 gallons of NSW on hand don't bother heating my NSW in fact right now it's in the mid 50's in that holding tank. I dont' even pay much attention to the salinity in there and only eyeball the salt input. Granted I am usually spot on when I add salt. I do however monitor my system salinity but the 5 gallons a day has little to no impact on my salinity in the short term so if the salinity in my mixed water is off by .001 or .002, it really has no short term impact on the system salinity nor does pH or anything else in the NSW. My Ca reactor keeps the rest of the important things in check. Best of all, I use the cheap Instant Ocean salt.
At the end of the day, I'm of the belief that a well planned out system with smaller daily water changes stays much more consistent in terms of parameters based on my experience. You don't end up with the build of nutrients between water changes which is typical of larger weekly or bi weekly water changes. That doesn't mean you don't need to peform husbandry such as vacuuming but it does result in more consistent water quality. That said, my tank is mostly bare bottom although I do have some large patches of sand. I don't vacuum ever though. Instead I have a lot of well planned out flow that prevents stuff from settling and insures that anything that does happen to settle in the sand or under the rocks is flushed off the bottom several times a day and suspended so it's sent into my overflow and exported by my filter socks and skimmer. The end result is that my tank is healthier than it has ever been in 20 years and the best part is that it requires the least amount of maintenance that it ever has. I don't think I put in much more than 1 hour a month including cleaning the viewing panes, feeding, weekly sock changes and mixing water.
