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...