Help with something found on corals

Hi,
I found two of my corals, GSP and Zoas affected by a white substance this morning. Pics attached but not very good at showing the problem. Tank parameters are, Alk 8.5, pH 7.9, phos 0, Ca 427, Mg 1465, Ammo 0, Nitrite 0, Nitrate 0. Tank has been up and running since end of October. Parameters have been stable for about 4weeks since adding BRS dosers for Alk (10ml per day) and All for Reef (2.8ml per day). Of course, I go out of town tomorrow leaving tank care to family to feed since everything else is automated. Any advice would be greatly appreciated. Worried about all my other corals that have not been affected yet. I could remove affected corals and place them in a newly cycled 20g for my clowns. They laid eggs every week and indirectly killed a couple other fish so they were banished from the 70g Thanks for your help!

Really hard to tell from you pictures with the blue light, 0 no3/po4 sounds like dinos though.

Can you take some photos in daylight? Best thing to do is usually go back to basics and make sure that your refractometer is calibrated dead-on-balls accurate, temp is correct and all of that.

Yes it is dinos, took a sample to LFS and they put it under the microscope. Dosing phosphate and nitrate to hopefully slowly bring everything up this week. So far inverts seem ok except I have not seen my sand conch since I got back yesterday.