Chalices suddenly losing tissue

[uscgbeachbum]

Tank been up and running over 3 years now. Just after Thanksgiving I had an issue with one of my Kessil A360WEs. I decided to move to (2) Hydra 26 HDs. Knowing that Kessils have UV I didn't think too much when I went to program my Hydras. I set the UV to around 50% and went about my business. Fast forward to about a week ago. I suddenly noticed (feels like overnight, but may have been over a couple of days) a complete bare spot in the middle of my pink boobies chalice about the size of a dime. My first thought was the UV was too high so I reduced the UV down to 10%. However, the bare spot is actually on the lower elevation of the chalice. I'd imagine if it was the UV it'd be higher, closer to the lights. Nothing else really wonky with the tank. I have a 2 part doser so my levels stay relatively stable. Ca ~ 350-380ppm and Alk ~ 9-10 dkh. For what its worth I've had my Mg > 1600 ppm for nearly 9 months trying to get rid of this red turf algae without success. I'll also add that I have a total of 5 chalices and this is only happening to my pink boobies. 3 of the other chalices are higher in the tank or more exposed to light than the pink boobies without issue.

Thanks in advance.

[aromano]

anything change in your flow. One of my chalices had encrusted over rocks over the years and a for want of better term an eddy developed over one spot from powerhead shifting position . Created a dead spot on the chalice about size of a dime/nickel.

[zaq11]

any thing around it irritating the chalice at night .
how is the water flow any change ?
try to dip in revive

[uscgbeachbum]

I haven't noticed a change in the flow. Tank is predominately zoas, shrooms, and a small handful of chalices.

Maybe i'll come out tonight after the lights have been off a while to peak around about irritants. Considering the rest of my chalices are file I'd guess it'd be localized to this one area.

[uscgbeachbum]

So I'm happy to report back with an update. It seems that I was able to stop the RTN at around day 8 after losing half the colony. I fragged some of the collateral damage with some bone cutters and am happy to report about 75% of the frags have lived. Lighting is still pretty low. I've done about 3 water changes and increased my calcium to around 410-420.