Urgent help needed Plate Coral - RTN?

[poiromaniax]

Hey guys,

I copied the template from detailed help so you guys can have a bit of info first:


Tank size:
1500X650X650

System Volume:
650L

How long has your tank been running?
6 months (80% of the rock was from my old setup running for 2 years)

What livestock do you have?
Sailfin Tang
Mimic Tang
Eibli Angel
Fairy Wrasse
6 X chromis
2 X Tomato Clowns
1 X Mandarin
Mated pair boxing shrimp
cleaner shrimp
Longspine Urchin
Nerita and Turbo Snails
Hermit crab
porcelain crab

Water Parameters:

Alkalinity (dkh): 8
Calcium: 430
Phosphate: 5ppm
Magnesium: 1300
pH: 8.0
Nitrite: 0
Nitrate: 5ppm
Ammonia: 0ppm
Salinity: 1.025
Temperature: 26

What lighting is over the tank?
3 X 150W MH (Bulbs changed 1.5 months ago) 2 X 54W actinic (bulbs changed 3 months ago)

Pumps and equipment:
Vortech MP40W
Sunsun 12000lph
ReefOcto DNW200 Skimmer
Phosban 150 with Antiphos

Maintenance:
Weekly 10% Water Change (Fighting GHA at the moment)
Siphon detritus

tests and additives (if necessary) bi weekly


Problem

So now that you have some info, my problem:

Yesterday I did a waterchange as I have done for the last 2 months,using Tropic Marin pro-reef matched to tank temp, salinity, etc. This morning I noticed that my green/pink plate had a few small white spots on it (more than spots actually, looked like lost tissue) Seeing as all my other corals were fine, I thought nothing of it,and I dismissed it.

I came home this afternoon and saw that the problem had gotten alot worse!

Pics:

Now:

1) What could be the cause?
2) What can I do to save my beloved plate?


Please help!!

Thanks gents

 

[459b]

Looks like somethings pecking it..perhaps the eibli? Does the long spine urcin ever crawl over it?

 

[Monti]

ok, well i cant see pics coz im surfing on my phone, but it isnt rtn if it started yesterday. Rtn is a few hours, and really there is nothing you can do if you get it. And urchins can be super pains on corals ime

 

[poiromaniax]

Looks like somethings pecking it..perhaps the eibli? Does the long spine urcin ever crawl over it?

I have never seen my urchin go on the rocks, he likes to stay on the glass. (seeing as I have plenty GHA there for him to eat )

ok, well i cant see pics coz im surfing on my phone, but it isnt rtn if it started yesterday. Rtn is a few hours, and really there is nothing you can do if you get it. And urchins can be super pains on corals ime

It didnt start yesterday. I did the WC yesterday and only noticed it this morning.

I really hope it isnt RTN Would hate to lose the cup coral

Doubt its the urchin, he doesnt like to go on the rocks.