Acan Heads Puckering then Dissapperaing?

[chickendude10]

Hi All,

 

My acans are receding in a way I haven't seen before. The colony seems to be healthy, but a head will just slowly start puckering up from one end and start melting. You can see the exposed skeleton on this image, as well as an adjacent head that is puckering/pinching at the base. 

 

The second image is showing a separate colony where the same thing is beginning. It's as if the green pigment is being pulled from the polyp, and the edges melting.

 

I think my Alk is on the high side for my nutrient levels, but my salt (Fritz) mixes to 10. Salifert tests show Phosphate around 0, but I don't run a skimmer so I find that hard to believe it's actually zero. I cannot see any pests. Most other coral seems to be fine with the exception of a Monti Digi that showed some STN due to alk swings a few weeks back. 

 

I feed LPS maybe 1x/week a mix of frozen mysis, Rod's, or New Life Spectrum pellets. 

 

Params:

 

Nitrate: 5

Phosphate: ~0 

Alk: 10

Calcium: 490

Mag: 1500

pH: 7.8

 

Any thoughts on what could be going on here and how to solve it? 

 

[Clown79]

Phosphate can be 0 without a skimmer

 

I've had issues with no phosphate in the past and have had no skimmers on my tank or refugium.

 

Lack of nutrients, alk fluctuations, too much flow would be the 3 issues.

 

Do you have a peppermint shrimp or other livestock that could be an issue

[chickendude10]

Thanks for the input. 
 

For stocking, I have:

1 Clown

1 Damsel

1 cleaner shrimp

Assortment of trochus, cerith, and nassarius snails 

 

I haven’t seen anyone bothering the acans yet, but I’ll be on the lookout. 

[jbb]

Watch the cleaner shrimp when you feed . It can damage the acans by ripping food out of their mouths. 

[Reefkid88]

With newer acan heads sometimes they will grow,then retract and eventually pop back up. 

 

 The cleaner shrimp may be snatching food out of its tentacles,maybe sensing that the polyp may be weak or know its tentacles aren't stick enough. I've had acan's where the tentacles were so stick it literally stick to my finger while feeding lol.  

 

 They whole colony looks healthy,I would just watch the shrimp.