acan recession

[spardoin]

I have 5 acans in my tank. all 5 have been doing great, but then yesterday I noticed that two of them were recessed. Just checked and they remain recessed. When I say recessed I mean the polyps are contracted and as a result I see skeleton.
The lighting and flow that they are receiving has not changed and are relatively consistent with the other 3 acans that are doing well. All other corals (SPS and LPS) seemed to be doing well. Should I be concerned? SHould I do something?
Parameters are great with exception that Mag and Calcium might be a little low.
PH 8.2, amonia = 0, nitrite = 0, nitrate, =.02. KH = 220, Calcium 400, magnesium 1300. This was based on parameters checked last night. I have since added calcium and mag, but have not checked it.

Deep Blue Professional 65G Reef Ready
36x18x24
Proflex II Sump 17.2 gallons
ESHOPPS PSK75 in pump skimmer
Maxspect Razor R420R LED Light Fixture 16000k, 27 inches

 

[camellia]

Are they closer to your power heads? I had one too close (under) a mp10 and it was really pissed!

If you see skeleton, you should be concerned!

 

[spardoin]

nope not anywhere near the powerheads

 

[just josh]

Some corals are temp sensitive and salinity sensitive...you have a swing with temps of w specific gravity??

Edit: Or*

 

[dough]

You did not mention the location you had them. All of mine and all the acans that I have keep over the years, have been on the bottom of my tank not directly under the light. I've also found out that acans are stung pretty easly by just about everything expect other acans. So I keep mine in a group.

 

[reef coffee & curly hair]

Acans generally do well with just shy of moderate flow and low to moderate light. Just like another mentioned, swings can affect individual specimens differently to varying degrees. And Chalices and acans do not play well. Sometimes acans tightly contract and come back on their own steam, but is generally not a good indicator of health/placement. Another real issue that is overlooked is these guys should NOT be placed directly (tissue touching/resting) on the sand as sand severely stresses the tissue and takes a good bit of energy to move/spit/secrete back out of the acans mouths and areas between the tissues and inhibits new growth. Tangs, blennies, and other algae eating fish may accidently pick at acans grazing for algae. If you run a low nutrient system then spot feeding and/or RedSea Reef Energy A/B type supplements may be needed for some specimens. If the tank is underfed like a low nutrient system then hermits and shrimp may pick at these guys even after they swallowed the food completely. This is very stressful on acans. I’ve also personally witnessed a large male emerald crab graze on one of my acans, was just scraping away. These guys are all day and all night scavengers and opportunists first and foremost. I also find slightly lower temps like 75-76 degrees are great for acans. Look for dissolved or jelly like areas that range in color from peach to brown and very little to a lot. If you see this try one of the coral dips like Revive first where you can see parasites fall off the specimen and lightly brush away any infections. If that doesn’t help, then try bayers (milky) as a dip. As a Last Resort try fragging the unhealthy areas off and using interceptor in a quarantine type setup. I mention this as there is some kind of worm that eats the food from the base of the acans mouth but these are rare and hard to see except when you frag you will see pin holes at the base of the acan skeletal structure. Clear close-up and area Pics could help you here. With all of that said just try moving this guy around first knowing the discretions mentioned earlier in this post. I apologize if I have left any good knowledge out. Best of Luck, I hope this may help.