I am using fritz salt. Don't have a answer to why this happens . Every time we do a water change we are changing the stability of the tank. This is why Triton doesn't do water changes. I was siphoning out detritus and changed only 50 gal in a 1200 gallon system. One wouldn't think this could happen but it did.
It makes sense I just don't know what to do.. because all I can say is on Red Sea my tank was a lot happier I just had precipitation issues that's the only reason why I am thinking of switching to Fritz.