Acans Closed Up. Help....

[Cahooligan]

I have 9 acan lord colonies. 8 of which are on the sand bed, and one on the rocks. ive had them all for at least 8 months, and they have been my fastest growing corals(besides zoanthids). none have been moved and no major changes have taken place. all of the colonies that are on the sandbed have been closed for about 10 days, and the only open colony is halfway up on the rocks. The tank is a 75g, and lighting is a 4bulb t5 fixture. a 25% water change was done yesterday in an attempt to try and fix whatever is wrong. i also tried moving another one up higher on the rocks to see what that will do. I see no parasites on them, nor are fish picking on them. the only evidence of picking ive seen is from a yellow tang, and only twice on one colony about 5 days ago. does anyone know what could be wrong? i dont want to lose them especially if it can be prevented.... thanks for any info or suggestions.

Params are as follows:
Ca: 440
Mag: 1300
Alk: 8dkh
Ph: 7.8
Nitrates: ~5

*everything else in the tank has been thriving. i have full polyp extension from everything else, along with continued growth. i run carbon and phosphate removers as well. thanks again for any help.

[greech]

Any flesh missing? Would have to suspect the tang at this point. Have you seen it go after anything else? Do the acans show a feeding response?

You mention everything else doing well but is it possible your bulbs are old? What other LPS do you have?

[Cahooligan]

No flesh missing and no receding. I see no feeding response out of any that are closeed up. I have yet to see the tang go after anything else besides that one acan twice.

[Cahooligan]

Bulbs are only about 2 months old. Other lps include hammer coral, frogspawn, a 9 inch wellsophyllia, 2 large open brains, a duncan frag, trumpet coral, and large australian prism favia.

[AndyH5512]

Your mag is OK by normal standards at 1300, but I know others with a large LPS load keep their mag around 1400. That said, I have the same issues with acans. No matter how easy anyone says they are, I just cant keep them happy. Everything else is colorful and growing, just not the acans.

[Cahooligan]

Well I've had some for over a year and have grown them into large colonies and just out of nowhere they closed up. I actually believe my mag to be around 1350 b/c I just dosed after my test came out at 1300... idk... its weird...

[Cahooligan]

I'm gonna bump this, because id really like some help. Could cyano cause an issue? We have a little on the sandbed, but its always been there unless its just now causing an issue?... new rodi filters should be here soon and maybe that will help idk....just really confused...

[Potsy]

There was a similar thread the other day: closed acans and seemingly cooperative tangs. The owner was advised to watch the tangs from a distance and it turned out that they were indeed nipping the acans. when the fish weren't distracted.

[Cahooligan]

ive read that thread a few times, and thats my suspect, but ive yet to see them nip at any...even if i watch from afar...and all of the colonies are closed up. not just one or two....