Grey spots


New member
Oct 3, 2021
Houston, TX
I've got every spreading grey spots on my plaster in ground pool. 13,000 gallons.

it started about 3 months ago wit the first spot I noticed, about the size of a dime. Now it's the size of a quarter and I have about 10-15 more.

I felt it, it have no different feel from the rest it the pool. It just feels like plaster. I've tried pumice stick, wire brush, and even used my power washer on it. Shocked (up to 12). Didn't even touch it.

The folks at the local pool stores, tried 3 different one, had no idea.

Metals, fertilizer, black mold. But no real idea. Do YOU have an idea?


Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Welcome to the forum!
Can you post some pictures of them? Does not sound like any kind of algae. More likely a plaster defect or calcium.
Please post a full set of test results from your own test kit if you can.
I suggest you read ABC's of Pool Water Chemistry.
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