HELP!! Im losing my Acan!

[zum14]

OK so i will try to attach pics(when i find a post that tells me how) i seem to have terrible luck with it. Ok so april 14 i noticed my acan wasn't fully inflated as normal and tentacles wernt out.. didn't think too much of it, just figured a crab or shrimp just went over it but continued to monitor, same yesterday, then today, its terrible, im seeing white on it and it doesnt look good. I dont really get why, it was starting to grow, all other corals are growing great (frogspawn, acropora, montipora, zoas, shrooms, xenia ) Nothing is close enough to take it out. Water perameters are as follows.

Salinity 1.0248
Ammonia unreadable
Nitrites unreadable
Nitrates unreadable
Phosphates Less then .25 but not 0
dKh 13
Calcium 420ppm
Ph 8.2

I do weekly 5% water changes, was due for one today but havent done it yet. Would really love to save him as i havent lost anything yet but fear hes too far gone. Any help would be great. Thanks.