Need help setting up doser-Calgary

[Coralgurl]

I've been using Seachem Salinity. In the bottom of my mixing bucket, there's a lot of build up on the bottom, but when I test, everything is good.

Today my parameters are as follows
Mag 1450
Ca 420
Dkh 6
Temp 78
Salinity 1.026
Phosphates between 0-10, hard to distinguish results

I've tested phosphates and ammonia 0

I noticed this morning, my wall frogspawn is now showing skeleton. I'm going to rescape my 55 and move him back over. This coral has done significantly well up till now, I paid $250 for it and have had it almost a year, not prepared to lose it.

I don't know what is going on and very frustrated. I dont know what to do at this point. I've lost $100's in corals over the past while and although the parameters have been a bit low, is this really enough to have this affect? What am I missing?