Why can't I keep duncans? :(

[Eclyps19]

I have *never* been able to keep duncans, and I'm going crazy trying to figure out why. Everything else in this frag tank is flourishing. I have a torch that's doubled in size over the last 4 months, I have a number of frogspawn/hammers that are super puffy, I have lots of acans, favia, some SPS, all do incredibly well in this tank. Throw a duncan in there, though, and nope!

Every single time I add a duncan, it looks great for the first week. Then over the next 2-6 weeks, I watch as it slowly loses its lengthy polyps. Eventually they will just barely be poking out of the skeleton. It may hang out like this for another few months, but eventually it will start losing flesh. The crazy thing is that they often start growing new heads just fine while in this constant state of retraction.

I've tried higher flow, lower flow, higher light, lower light, nothing seems to keep them happy.

My params are pretty constant.

Alk: ~8.0
Calc: 480
Mag: 1400
N03: ~5-10
P04: ~0.02 - 0.08
Salinity: 1.025
Lights: AP700

Everything else does great. WHY CAN I NOT HAVE NICE DUNCANS?

Examples:

After a couple days:

After 1 week:

After 2 weeks

One of my long-time duncans who's been closed up for about 4 months (grew about 4 heads while closed up):

 

[DarthSimon]

I have had the same issues. They do tend to like lower flow and low to medium lighting...

I found a few suspect fish picking on mine in time... The Foxface was the culprit.

What fish do you have???
Also how’s the flow down there??
Is that a frag tank???

 

[Eclyps19]

I converted the tank into a frag tank about 2.5 months ago, so entirely fish free right now. I would say that flow is low in that spot, light is medium. I just moved it to the furthest corner of the tank from the lights and the powerhead. I don’t expect this to have any impact, but I’ll give it a shot. I’m trying to quarantine this one for 45 days before moving it to my larger tank, but if it looks like it’s about to kick the bucket, I may make the move sooner. This is a really beautiful one that I’d hate to lose.

 

[DarthSimon]

Do you happen to know what par levels are where Duncan’s are located??

 

[DarthSimon]

I see micro bubbles attached to your frag rack on 2 of your photos above. Do you have Dino’s? Or some sort of Cyano bacteria growing in your frag tank? Anything collecting on coral flesh or skeletons?

 

[Eclyps19]

No PAR readings for this tank, just eyeballing it. I have my acans and euphyllia doing VERY well on the sand bed both directly under and surrounding the lights, and I would expect the duncans to do well in similar lighting. These ones have been on a holder about 3” above the sand bed, so maybe moving it down will help.

Good catch with the bubbles. I did have a nasty dino outbreak about 5 months ago. It’s been well under control since then, however I let my n04 and p04 get a little too low recently and they started to creep back in. I wouldnt consider it an outbreak, just a few spots here and there. Nothing on any flesh of any corals. I do suppose that it’s possible that the small UV that I have running is still killing those off and releasing some toxins. I stopped running activated carbon after I won the big battle, but maybe I should keep it going. If that’s the culprit, it’s just odd to me that it’s ONLY affecting duncans. Maybe it’s something that they are especially sensitive to, though...