I do about 200 Gal every two weeks. Once I get more calurpa and sponges going on the refugium I think I will change that to every three weeks. The Ozone and giant skimmers seem to keep the water very clean. I guess I figure if you don't have a reef and are not in need of trace elements and your nitrate and phosphate are low then you don't need as much of a change.
I usually wait for a sale and then buy about 25 buckets.
One of the things I found that help me keep the tank clean is a lot of water flow in wave and pulse mode in addition to a bare bottom tank. I also change the filter socks every other day. There is never any food or poop that lingers in the tank long.
I feed about four to five times a day but make sure the food is gone in two minutes or less. usually it is gone in 30 seconds. The good thing is that the tank has a lot of algea for the tangs and even the angels to graze on. Also believe it or not when a large fish poops there is a feeding frenzy. A whole sheet of nori lasts about 20 seconds in that tank.
The water stays exceptionally clear. As a matter of fact per the ORP probe it is in the high 390s but that is subjective.
I had a long battle with a rare parasite and I spent over two thousand dollars on drugs and could not get rid of it. Believe me when I tell you i buy from the best place (DD) and QT for four weeks. Even through all that someting like a fluke but not one that responds to prazi got in. I fought it to the point of almost giving up. As a last resort I tried a total of 460W UV, 750 mg/hr Ozone and metronidazole in the feed once a week. I have not seen a sign of that parasite in a while (couple of months) but it does not mean it is gone. Have my fingers crossed
the parasite would only attack fish with large scales, only in a few places and looked like a little tiny worm that would leave a wound. It was not an instant killer but I could tell the fish were not happy. I have a library of fish books, over 100 of them including Noga's and a high powered microscope but I was not competent enough to really figure out what this thing was.
Before this, having had fish for over a decade without an illness I was not emotionally prepared. My wife certainly was not prepared for me to deal with what i had to do (get all rocks out, catch fish in such a large tank and find QT for all of them all over the house with two little kids). That was a huge project on its own. Hopefully that is behind me.
thakfully through the whole ordeal wich lasted about a year (very long) I only lost a couple of large fish and some small fish (four chromis and two fairy wrasses). At one point I thought i would loose them all but taking them into QT, doing a water change (small) everyday where I was syphoning water from the bottom of the tank (using a mag 350) performed miracles. All fish for the last couple of months have been eating like food was going out of style, the fins look good and everyone comes to greet who ever walks by the tank so I think atleast the issue is under control. I have not seen any signs laterly but that does not mean it is gone. I am obsessive about checking out my fish.