Water changes

[Quagmire]

I do 50% weekly water changes and have never had a problem.I try to match salinity,temp and buffer my alk couple dkh higher, ph is usually close .But they are never an exact match.The only problem I can think of when doing a large emergency w/c,as long as parameters are in order might be light shock due to better light penetration in clean water.Think of the ocean,an area the size of our tanks get a 100% w\c numerous times a day.