Softies take turns deflating - another coral mystery!

[Fritz05]

A couple of days ago the water in my 65g mixed reef turned slightly milky. Fish, inverts, LPS and SPS corals were unaffected. But some of my softies (toadstool, green hairy mushroom, alien hand sinularia) deflated, but not at the same time. They “took turns”, some deflated in the morning when others were fine, then in the afternoon they switched and the deflated ones extended and the other ones deflated. My toadstool mushroom was unaffected, as were my zoas. I cleared up the water with a UV sterilizer. I could not determine the cause of the milky water, as no inhabitant had died. However, after a couple of days the cloudy water returned and so did the situation with the corals (Incl. the “turn taking”).
Water parameters are unchanged : 35ppt, 8.3 alk, 8.2 ph, nitrates 5, calcium 400, phos <0.03

Any ideas what is going on?

 

[doubleshot00]

Do an icp test and keep the uv running.