What is this??

[EmilyOTR]

it doesn't come off with a brush. it's slowly disintegrating with chlorine. I have it in several spots around the pool. the water is crystal clear.

 

[Jimrahbe]

Emily,

It looks like a calcium nodule..

How old is the plaster? Has the pool ever been replastered?

Let's see what others say..

Thanks,

Jim R.

 

[EmilyOTR]

Emily,

It looks like a calcium nodule..

How old is the plaster? Has the pool ever been replastered?

Let's see what others say..

Thanks,

Jim R.

I wasn't the owner but I was told it was replastered in 2013. this happened in several places in my pool this year when I opened to a green pool (due to cover water getting in over the winter). the only other time I've seen this was the year a tree branch poked a hole in my cover and I opened to almost no water and some of this. that time, I didn't have algae as I passed the OCLT right away. Currently my pool looks amazing besides this in a few places and I can't pass the OCLT.