Diatoms on SPS tips?

[dcw1sfu]

Have two frags in my tank that look like they have a small dusting of diatoms on the tips. It can not be blown off with a turkey baster and not sure if it's harming the corals. Showed up approx 2 days after a 20 % water change. I have no other signs of algae or diatoms in my tank and in fact I only have to clean the glass every week at this point.

Paramayers as of this morning during lights out:

Nitrate between 5-10 ppm
Phosphate .01 Hanna ULR
Calcium 420
Alk 7.3
Mag 1300


Here's a Pic if you can make it out. Its kinda washed out but the coral is light pink with polyps below the tips.

 

[71xlch]

picture is super blurry but from what i can see it looks dead. No polyps visible and bone white. Almost looks like you can see the detail of the skeleton. I could be way off due to a bad picture.

 

[degibson84]

I was thinking the same thing.

 

[reefmutt]

Looks like alk burn or something..
Coral is certainly dead on the tip and doesn't look too healthy..
What light are you using?
How old is the tank?
How many other acroporas do you have?

 

[whitrose02]

Looks like mostly skeleton to me too.

 

[SoloGarth]

Algae will not grow on long coral tissue. If you see it that means you now have coral skeleton. Which really is also pretty awesome once it gets big enough.