Protein Skimmer and Coral issues

[Antrias]

Hi Everyone,

I have had my tank going for 6 months now with relatively no problems. However now I have two problems are are driving me nuts! The first is my protein skimmer use to be dead silent (reef octopus diablo Dcs-170) now it is making air gurgling noise - air flapping. So I took the pump and gave it a good cleaning and got all the salt build up on the part that connects the air tube to the pump thinking that would solve them.problem for sure. But not didn't make a difference! I hate the noise what can I do to get it back to silent?

Second problem is my candy coral used to be really healthy. All my other coral looks fine except the candy corals heads are shrinking. Any tips?