Frogspawn falling off skeleton-please help

[reeferkiss]

In the last week, several heads on my frogspawn corals have been falling off. They showed no signs of being unhealthy before this, and the heads are just sitting there in the sand bed, still plump and extended. I have two batches in two different areas of tank and it is happening to both. No other coral or organisms seem to be affected. All my parameters seem pretty normal. The magnesium looks a bit low, I am supplementing that now. Any other ideas? I'm pretty upset as these guys have grown with the tank from a little bud for 3 years now.

Salinity .026
pH 8.2
Temp 78-80
Ca=460
Mag 1020
Alk 12.5
Nitrate=~10
Nitrite/Am=0
Flow in area of frogspawn=moderate
Level in Tank=mid
Lights=2 Metal Halide 150s + 2 each 420/460 T5s

[organism]

Alk seems a bit high, but how are you measuring your salinity? If it's a refractometer, have you calibrated it with calibration fluid recently?

[RokleM]

Magnesium is critically low IMO. I would get that up ASAP (1250-1300 range at least) and also check the salinity as organism mentioned.

[reeferkiss]

I agree about the magnesium and am working on that. Yes my refractometer is calibrated. Do you think the magnesium could have caused this problem?

[RokleM]

While some won't agree, IMO absolutely. Low MAG is the one and only reason my LPS have ever receded.

[stingythingy45]

Most definitely bump that Mg. up to at least 1250 ppm.
Depending on the size of the tank,that could take a lot of suppliment.
Hopefully that alk didn't spike too fast.But generally lps can handle that,sps on the other hand,not so good.