its a 125 and yes once a month. sometimes every six weeks. corals did fine before on that water change schedule...use calcium and trace elements supplements from kent. the lps that are receding are most of my brains and hammer coral. you can tell the receding is gradual. because there is barely any white showing. also, i have no algae blooms. have a few pest anemones that i need to get some joe's for. use ro water. but haven't changed my filter in about over a year. i use amquel for each water change to be safe on chlorine. have a dusky wrasse, yellow coris, pajama cardinals, naso, and an 8 inch purple tang, royal gamma, and 3 green chromis. have a few zoas...most of them have died as well. some softies as in mushrooms which seem to be florishing more than usual. tons of snails and a few hermits. two urchins. one urchin i have no idea what it is. can't identify. it was a hitch hiker. deep sand bed. have a few fire worms that the wrasses do a good job of keeping under control. some astreas, but not pesty. run a sump with skimmer uv sterlizer and phosphate reactor with phosban. have 2 250w 14k metal halides with atinics. only feed once daily flakes and pellets, shrimp every so often. i'd be happy to answer any other question, just shoot.