Something strange going on in my tank

[Vincent100]

Hi guys a gals

Lost a head on my torch .... picture
Watched it die over a day other head is fine
Anyway there's some strange white stuff over the skeleton looks like sponge but it's not
Also had a little rock with a few blasto heads on it ,today they are dead and have the same white stuff on them ,took the rock out and it stunk of egg

Water

Mag 1410
Alk 8.6
Cal 430

No3 0.02 I think maybe a bit higher
Po4 0.03

pH 8.1 to ,8.2
Temp ranging from night to day 26.6c
to 27.0c sometimes might go as high as 27.4 with the house heating on

Going to do a 75 liter water change today
Tank is a red sea 350
Lots of rock and lots of corals and fish

Changed a few Rocks last week because the old ones had hydroids

Any help would be great
Going out now so might not be able to reply for a bit but will do as soon as I get home
Thanks

 

[Diesel]

I'm thinking about a slime decease or bacterial
You can dipp corals in a iodine solution to stop it from spreading but in most cases if water quality is good it will stop it self
Remove all corals that is or shows the white skin.
Over rated flow and lots of water changes can be a good friend right now.
Keep testing N03 and make sure you target at least 2ppm not 0.02 as that's to low.