Mushroom coral stopped opening up??

[easperhe]

All,

Suddenly, my mushroom corals are not opening up. There are no aggressive corals around them. so, not sure what gives (see picture).

The only two things I can think of are
* my alkalinity is low (6.3) but the pH is normal 8.0-8.3.
* I just found a dead snail on the top of the glass rim above the rock where mushroom corals are. It definitely smelled and I didn't notice it for awhile since it was under acrylic fan stand. But, how would this negatively impact coral in the water?

thoughts?

thanks!

 

[easperhe]

FYI - the other water parameters are fine

NO3: 0.5ppm
PO4: 0
Calcium: 430
Alk: 6.3 dkh
Mag: 1350

they had been doing very well. then all of a sudden, they closed up.

 

[mayjong]

get the kh up ()slowly)
check the salinity, too. softies can be especially sensitive to that imo...