Can't figure out why my frogspawn is receding pH problem?

[reefsafehokie]

I have had this ~50 head frogspawn for 6 years. Over the past month or so I've noticed the heads are receding. Some are receded all the way into the skeleton. I haven't added anything new into the tank since November and nothing has changed. Tank is a 120 gallon reef with a 40 gallon sump. Euroreef skimmer - havent been using it because its so loud. I change out 20-30 gallons every 2-3 weeks. There are only 2 damsels, a blenny, some peppermint shrimp, and brittle stars in the tank with it. They also have been in the tank for years and never picked at it before.

Water parameters:

pH 7.7
KH - 9' or 161.1 ppm KH
Calcium 400
Ammonia 0
Nitrite 0
Nitrate 0

I have inspected it at night, don't see any pathogens or anything picking on it. No brown jelly. I've had this before and know what to look for.

The pH of my tank usually higher. I've been a little lazy about dosing calcium lately, been busy trying to graduate. Could the pH be causing it to recede? That's the only thing I can think of..

I usually dose every few days with C balance 2 part calcium buffer and weekly with iodine.

Should I do iodine dips? I've definitely lost a few heads.

 

[Dkuhlmann]

How old are your lights?

 

[likefish]

I am curious to hear if anyone else has any input. I have a tank euphilia tank that has many of the heads shrinking as well. THere are several varieties in this tank and only some of them are shrinking.

Any advice, links or input appreciated!

 

[fishresponse]

Your pH is pretty low. What's your magnesium level? Also, from your pics, it looks like your frogspawn appear brownish. Do you spot feed your corals? These guys have mouths on each head and will eat. I've always found that by feeding any LPS coral, it will help color and growth.