I have the same stuff that just started showing up here in my pond in Ontario this week. I have attached a few pictures of it. Last year I had the same thing happen but after I had been gone for a week and power outage reset my timers and I had no air for the week. When I got back the pond had a major bloom going, killed about 6 brown trout and larger perch. Turned the diffusers back on and by the next day the green was gone and I had the rusty looking scum for a week or two.
This year, the pond was perfect (I have kept the pond died pretty hard as I still have about 25 brookies and all my browns and tigers still alive and doing well) and I wanted to keep the temps down. In the last week our air temps have been in the low 90's and the surface temp is just getting into the 80's now. Yesterday the rust colored scum started showing up pretty good as well as a few matts of floating algea. I am wondering if I had a mild bloom going and it died off. So far, so good though and no fish are floating!
