Few things about doing big changes. One, it has been said that RTN could occur on some sps corals. I never had that issue but it was blamed at times. Personally I think lots of factors plays on that, making rapid changes like ca, mg all along with temp & salinity all at one could have impact.
So to avoid that I recommend aerating your salt mix over night, using a calibrated refract or floater hydrometer to get precise measurements. Temp. should be the same, along with your other levels as to lesson any chance of shock. Also If your making up large batches in multiple containers, this makes it even harder to all be the same, so if possible mix in one large container or mix into one as your replacing water.
Tanks this size makes doing bigger changes harder so a little more care should be taken. I'd space out your big changes some, do it over a couple weeks, each time trying to purge the rocks etc. from as much accumulated detritus possible, it will take a while to see results.
As far as that unit, it is designed more so for your area, they do recommend UV etc If you have other concerns or live elsewhere. Also remember anything can change without your notice. At least get your water tested at a lab every so often to make sure that at your home it is just as good. Claiming it is almost as good as distilled could be misleading.
