Systemic coral death, HELP

[SeamusHarper]

In a span of a week, many of my corals have died suddenly.

Last week, a giant torch that has been in the tank for over 4 months died within three days, losing many tentacles a day, leaving only a brown stump.

My hammer coral followed the same process a few days later and now it's gone.

This morning I awoke to find the skin peeling off my Jack O Lantern, exposing white skeleton below. I also noticed a small white worm travelling along the edge so perhaps this is the culprit?

I'm also noticing webbing hanging off some of the corals, I have no idea what's going on!

Nothing has been added to the tank for over 2 months.

Temp: 77-78

Ammonia: 0 ppm

Nitrite: 0 ppm

Nitrate: ~20 ppm

pH: 8.2

Alkalinity: 9 dKH

Calcium: 400 ppm

Magnesium: 1,200 ppm

Salinity: 1.025

 

[EnterName]

If you have photos of the issue or the whole tank this could help the community to help you
Turn off the heavy blue lights and use neutral/white light if you take photos, this usually helps to keep things visible.


As for the white worm, it's hard to tell without images, but many organisms will simply profit from the biofilm that establishes when corals die, so it might just be something that helps to clean up the dead tissue.

Phosphate, flow, and light are the next potential candidates to check, and finally an ICP-MS test would help to find out if something like copper or zinc got into your tank. There are obviously more dangerous substances, but those can be introduced quite easily and are extremely toxic to corals.

 

[SeamusHarper]

Here is the Jack this morning

 

[EnterName]

(Ex)aiptasia can hurt corals and "walk" so this obviously can cause tissue necrosis, but then the edges of the coral would be hurt, not something in the middle.

That guy however, looks a bit more suspicious. I can't identify it properly, but maybe, that's the issue.

 

[SeamusHarper]

I haven't observed the (Ex)aiptasia moving, it's been stuck to that coral since it was placed in the tank months ago from what I have seen (it may be moving around and returning to it's spot I suppose). Should I remove it?

The worm disappeared shortly after I took the picture unfortunately.