frogspawn problems

[sealover113]

I have a 135 gal. reef tank that's been set up since Feb. About 2 1/2 or 3 months ago I purchased a 5 branch frogspawn. About 3 weeks to a month ago one of the branches died off for no apparent reason. All the other corals in the tank are fine, hammer, xenia, kenya. Ph is 8.2. Ammonia, nitrite are fine. Nitrate is about 20. the last time I checked the Calcium it was about 450. Now another branch seems to be withering. I don't know what to check. It is in light flow, in about the middle of the tank. We have compact flor. in the tank. If anybody has any ideas I would appreciate it. I would hate to lose it and we are still a little new to the hobby, 1 yr. or so. Thanks!!
Alyssa