Dark stains in pool

[kenpee]

I’ve been noticing more and more quarter sized stains in pool recently (pics attached). They’re raised when I touch although I can’t easily scrape the material off. I have a SWG. Is it salt building up? What could the cause and remedy be?

 

[ajw22]

I cannot see anything in the pictures, but it sounds like calcium nodules if they are raised.

How old is the plaster?

Has the pool been replastered?

Plaster Installation and Maintenance - Further Reading

www.troublefreepool.com

Calcium Nodules in pools What are calcium nodules? In swimming pools and spas, they are small mounds, bumps, deposits, or “slag” piles of calcium carbonate which are formed from material that has been released from the plaster. The small calcium nodules are rough to the touch, hard, and generally gritty. Nodules may form singularly (far apart or sporadically), or many and close together along a crack in the plaster surface.

Unusual Calcium Nodules About a dozen years ago, the onBalance team began investigating a slightly different and smaller type of nodule in recently plastered pools. Some of the nodules had not developed on delamination cracks, but instead, they had formed on severe “crazing” or “check” cracks that were nearly invisible. See photos of small nodules

 

[kenpee]

Pool was resurfaced in 2021.

 

[ajw22]

Pool was resurfaced in 2021.

Calcium nodules are more likely in a resurfaced pool.

 

[kenpee]

Pool company said it’s likely calcium and one of two things may be needed:
1. Add chemicals for a week that takes care of it.
2. Replaster the pool if that doesn’t work.

I’m very frustrated, as we just plastered it in 2021.

Any advice for learning more and trying to figure out if it truly needs to be replastered or not?

 

[ajw22]

Live with it.

It is not a reason to replaster the pool and there is no guarantee it will not occur again.

What harm is it doing?