Colt Coral sick

[Chaloupa]

I have 2 colts...1 large about 1.5 feet away from this one that routinely shrivels and "melts". It is never fully extended as when I bought it. My water;
SG 1.025
pH 8.2
Temp 83 (chiller arrived today as the temp is getting too high already but coral does this at lower temps)
Alk 9.9-10
Calcium 320+
Nitrate 5-10 (had sun polyps that were keeping them up a bit higher)

I water change every 10-14 days with RO/DI water, Seachem Reef salt, made up before hand up to temp etc,

Tank is a 65 gallon hex with a 20 gallon sump, a Coralife Aqualight pro with a 150watt halide bulb, Remora Pro skimmer...not sure what else you may need here for help but this coral needs HELP!

 

[Dani Arnanz]

What about the white areas on the right of the pic? It could be interesting to take a look at the night searching for a plague, for example the nudibranch Tritonipsilla elegans, eats soft corals, and itÃ"šÃ‚´s probably the most common nudi which arrive with corals. Also some worms could be eating your coral.

Good luck!