URGENT Montipora Problems

[NSS]

Got these red Montiporas about 4 months ago. All went well until 5 days ago. Every morning since the last few days i've noticed more missing tissue. Are these worms eating the flesh or something else?
I have checked at night if I can see any critters, but nothing.
The polyps are extending well, so I don't think that there is anything wrong with my parameters. I have other SPS and LPS in the tank and they are also all fine. No new fish added. I have a pair of clowns, a pair of chromis and a Melanurus Wrasse. I've had him for years and he's never nipped on anything coral related.

Dosing ATI Essentials Plus: Alk 8.9, Cal 465, Mag 1380
Tropic Marin: Trace Elements A- & K+
All other parameters have been stable since 3 years in this tank.

 

[bluemon]

What worms are you talking about?

Nitrate and phosphate levels?
Salinity?
Any recent changes?

 

[NSS]

Nitrate 6ppm, Phosphate 0.1ppm
Salinity 1.026
No changes except adding these Montis. I did have a quick dkh spike 2 weeks ago going to 10.2.
Regarding worms: I'm just throwing it out there, asking if this could be the work of worms or nudibranches, but I have not seen anything on the corals by day or by night.

 

[bluemon]

The alk spike might have started a STN as you already run high Alk to begin with.

Do you have other montipora?

 

[NSS]

no other montipora. i have 2 different pavona, 2 different acros, a stylo and a birdsnest. all established colonies. They are all looking good.
Should i try a iodine dip for the monties?

 

[Mr. Mojo Rising]

I agree, alk spikes can trigger rtn/stn.
I don't see any worms or pests in your pic.

 

[NSS]

thanks for the help. did an iodine dip today and placed them a bit lower in the tank. they are very slimey and don't look great now, but I hope they will recover. Nothing more i can do. I will report back for the record in a week.

 

[punky_rymn]

thanks for the help. did an iodine dip today and placed them a bit lower in the tank. they are very slimey and don't look great now, but I hope they will recover. Nothing more i can do. I will report back for the record in a week.

What ended up happening after waiting a week?