Acan Retracting

[XenoBE]

Ahoi hoi,

First post here and pretty new to the hobby. I'm in need of some advice of why my Acan could be retracting.

I've been running an Aqua Medic Blenny Qube since February. 76 liters (20 gallons). All material is stock.
This hobby kept me sane during lockdown and it has become something i value highly.

I've lost some turbo-snails in the process but after banishing a hermit crab to the sump, that has stopped. I've lost a Duncan to vermetid snails but they seem largely gone now.
Other than that, things have been going rather well and as far as i can tell, everything looks happy.
I'm abit in doubt about my Goniopora frag who stays retracted most of the day.

The Acan (right?) in the center i've had for about a month. Two polyps at the front of the colony (excuse me if i'm using the wrong words. feel free to correct me) seem to be retracting and i have no idea why. The other Polyps seem to be well.

Parameters are:
* Sal. 1.025
* Temp. 26° C
* KH/Alk: 8,8
* PH: 8,2
* NO2: 0
* NO3: 1
* PO4: 0
* NH3: < 0,15 (it's probably 0 but it's difficult to tell the difference between the two colours)
* Ca: 400
* Mg: 1290

I dose a drop or two of Manganese every other day, along with one drop of Aquaforest AF Vitality.
I spotfeed the corals Aqua Marin Ocean Plankton (the red kind) every 3 days.

3 pictures attached: front view to give a general feeling (don't worry about the frag in the front. it was a rescue attempt. i should probably remove it), one close-up of the retracted flesh earlier this week and one today to show the "progress".

Any help or opinions would be appreciated.

 

[Chuk]

What kind of light do you have and how are you running it? It could be too little or even too much light depending on the settings and intensity. Flow could be a issue as well. My experience is they like lower to medium flow so if it gets too high they shrivel up and can start to strip flesh.
Why do you dose manganese are you deficient or is that something you just heard to do?

Also, what livestock do you have besides what is in the picture. There are plenty of things that can pick at or irritate acans like a shrimp stealing food from it.

 

[XenoBE]

Thanks for the reply.

Lighting is the Qube 50 that came with the tank. I run it through a seperate control module with the standard 2h blue light, 4-ish hours white light, 2h blue light cycle. I haven't lowered the intensity. Is there a way to measure/know that, aside from a PAR meter?
Their website says: 1250 µmol m-2s-1 with 834 lm
If Goniopora tend to keep "closed" in light that is too bright, that might indicate this too. I'll try tampering with intensity abit.

I've always had the flow to about half strength in a wave pattern so that the Euphyllia in the front has a more gentle motion.
I'll try lowering it even further then, though i always had the feeling half-setting was barely enough to keep the water clear from dust-particles. (if that makes sense....)

Manganese was advised by the LFS when i asked why the Goniopora kept "closed" most of the time. I did see it made an improvement but not that much.

Visible livestock is a Polymnus, a cleaner shrimp, a Pictus blenny. Other livestock is another Polymnus, two turbo snails, a babylonia snail and a blue hermit crab.
I keep a close eye on the hermit whenever i can. I see it quite often but never near the Acan.
The cleaner shrimp tries to steal food and it's a 15 minute struggle to keep it away, but it works. It always goes for the Blastomussa's. I've never seen it pick the Acan.

 

[Chuk]

Ive always heard Babylon snails aren’t reef safe and that they eat clams and can eat other snails so keep an eye on those guys when they come out at night. I’ve never kept them for that reason.

Par measurements are definitely the most accurate way to get a read on your lighting. Otherwise it’s pretty much trail and error, to be fair I’ve not measured my own par so when I put corals in its kind of a shell game moving it up and down until I find a spot it seems to like.

I can’t help with the Goni I’ve never been able to keep them so I’m not sure what they really like.

 

[vetteguy53081]

Nitrate slightly up but not the answer.
Assure your salinity isn’t higher from a false reading.
Moderate light and water flow, feed 2-3x per week and keep acan off the lower part of tank as it will get irritated by sand.
Light seems to be a little bright . Lower whites a little