Frogspawn and duncan corals not extending polyps

[oldRash]

I've got a bit of a mystery on my hands with my frogspawn and duncan colonies. They just stopped extending their polyps over a month ago, and it's been driving me crazy. They'll slightly start to extend, then immediately recede - it's like they're teasing me. They don't seem to be dying or anything, but they're not eating or extending, which is weird.

I'm stumped. This all started right before I moved everything to my new 285 gallon tank. I've double-checked all my water parameters, and they're perfect - 0 ammonia, 0 nitrite, less than 5ppm Nitrate, Cal 420, Mag 1200. I've even tried spot feeding to see if I can get them to extend to eat, but nothing's working.

I'm really at a loss for ideas here. Has anyone else ever dealt with something like this?

[RockfordE4]

I had a similar issue with my LPS corals last year and it was due to low alkalinity levels. Check your alk levels, it might be the culprit. LPS corals tend to retract when alk is low.

[ravenoak]

Alk and Mg levels need a double-check, Mg's a bit off, should be around 1350.