Need urgent help to identify disease

[Dule T&T]

Hi everyone.
Out of nowhere I noticed that almost all my LPS corals (except Euphyllias) have small "bumps" of mesenterial filaments hanging around tissue edges, and those edges look like they're slightly swollen or something and like they are receding.
It's a large system with literally hundreds of corals - some of them extremely expensive (like this Acanthophyllia from the picture)

All parameters are in perfect order and stable for a very long time.
(The only thing that is possibly slightly off is Mg - 1400 ppm. But it's like that for a very long time, and it wasn't problem before.)
It's a 6 years old system.
Nothing was added to the tank for at least 6 months.

I have no clue what the heck is going on here, but it doesn't look good.
I tried googling these symptoms but I didn't find anything.

Oh, by the way, dipping corals, of course, didn't change absolutely anything.

Any help would be highly appreciated.

 

[mdb_talon]

Never seen that happen across a whole tank. I don't know the issue, but if it were me my first step would be carbon/chemipure if you don't use it already in case there is some chemical or something that made its way to tank.

 

[Dule T&T]

Never seen that happen across a whole tank. I don't know the issue, but if it were me my first step would be carbon/chemipure if you don't use it already in case there is some chemical or something that made its way to tank.

I'm using Brightwell purit.

Any idea what could cause it?
It's driving me crazy because I know that everything is the best possible order.
What am I missing?

 

[Dule T&T]

Come on guys... no one ever saw anything like this?
...I thought all reef experts are on this forum

 

[Cell]

Post full parameters and a full tank shot.

 

[Dule T&T]

Post full parameters and a full tank shot.

Ca = 440-450
KH = 10
Mg = 1400
PH = 8.2
SG = 1.026
NO3 = 5
PO4 = 0.01
NH3 and NO2 - undetectable
I ~ 0.06 - ish
Sr ~ 10 - ish

Temp 24-25C
System volume 500g, 10 feet long display tank.....
Lighting - Radions XR30PRO G5

Using Brightwell Purit as chemical filtration, nothing else is necessary.
Doing 5% weekly water changes - mostly because of my OCD not because it's necessary.
Dosing Ca and Alk daily....
Occasionally in the past I was dosing some NO3 (Brigtwell nitrogen) to keep NO3 above 5 ppm for my LPS because tank was too clean.... but now I just increased feeding from twice a day to three times a day and NO3 stabilized at 5 for about a year now.
Occasionally I'm dosing AB+
Feeding tank with zooplankton as well, also spot feeding corals with mysis 2 times a week depending on my free time and how late I am up at night hahaha

I am not by my tank right now, so I can't take pics.
Maybe I send some later.