Tissue Recession / Loss in Established Reef

[IronChefItaly]

Can't quite nail this issue down...
So I've been experiencing a bit more volatility in my tank lately than I would like and I can't seem to pinpoint the issue. Basically I'm observing signs of stress from my more delicate corals but my tests aren't showing any issues. I have a derasa, crocea and maxima clam, sponges, two dedicated rocks for anemones and zoanthids, elegance, dendrophyllia, and an abundance of euphyllia and other LPS all of which are not showing any signs of stress - yet.

The issue... periodic tissue loss beginning from the base of sps and minor tissue recession from the edge/tips of pectinia, chalice and scolymia.

Parameters... (tested weekly with Red Sea kits)
Salinity - 1.025
Temp - 77.5
Alk - 9.8 dkh
Calcium - 450 ppm
Magnesium - 1300 ppm
Nitrate - 1.0 ppm
Phosphate - 0.05 ppm

Other observations...
• 23% water changes done every two weeks, noticeable improvement in coral health in days following
• Tissue recession / loss doesn't appear to be occurring all the time. Rather during periods of low attention and overall maintenance.
• Pectinia and chalice coral tissue seems to be deflated or tight against the skeleton during these trouble periods.
• No observed changes in parameters or nutrients in these periods.

System...
Red Sea Reefer 250 - 65 gallons
Razor LED
Bubble Magus NAC 3.5 skimmer
Activated carbon
Chaeto refugium
Dose seachem fusion 1 and 2 and Red Sea NOPO-X


http://imgur.com/BaLyIEa
http://imgur.com/4n4RBor
http://imgur.com/V1YpNR5
http://imgur.com/15NznUp
http://imgur.com/KgOmYU2
http://imgur.com/Oybq5LW
http://imgur.com/RZ7rBwM
http://imgur.com/7G0BhlI

I would greatly appreciate hearing any thoughts or similar experiences. And as always, thanks for reading!