We recently purchased a home with a 23,000 gallon in-ground vinyl pool (Hayward) with a sand filter. All-in-all the pool appears to be fine with crystal clear water and based on frequent testing the water chemistry appears good. The only two factors of concern chemically are that the water hardness is low (I'm working on that) and the test strips that test for such things indicate that the stabilizer is on the high side. I've never added stabilizer so I've no idea why this would be.

My primary concern is that we are getting these semi-translucent thin patches of stuff floating on the surface of the water. They have a texture to them and at first I thought they were some sort of insect eggs but clearly they are something else. They are visible only looking at the surface of the pool from an angle in the light otherwise the pool water is perfectly clear. The pool is some years old but has been well cared for by the previous owner.

Online I'm reading about white paper mold but this stuff is only on the service of the pool nothing no note when submerged.

I've been using two variants of shock normally 2 pounds at a time -- sodium dichloro-s-triazinetrione 58.2 percent and trichloro-s-triazinetrione 53.5 percent. These are probably the same thing with slightly different names.

Since the instructions say one pound to every 10k of water I've been rounding down for our 23,000 gallon pool. Maybe I should be rounding up.

Anyway, with the off chance that I've not super-chlorinated it enough I'm going to add 3 or 4 pounds tonight to really kick the water in the butt.

Any suggestions for what could be causing these floating patches?

Thanks for sharing.

Justin