Plaster damage?


Jun 26, 2016
Ashton, MD
Hello all,
I'm dealing with what appears to be plaster failure in my 30k gunite pool and any assistance from the forum members is greatly appreciated.

When closing each year I drain the pool below the return lines (roughly 24") in order to blow out/plug the pipes; always open to a full pool based on the use of a mesh cover/rain and snow. Opening readings (K2006) in early May showed CH 100, TA 20 and high PH (dark red).

When we removed the cover this spring we found embedded algae stains that have not come out over the last weeks as we brought the water into balance. Current readings are FC 3, CH 375, TA 80, PH 7.8, CYA 70 (the water looks the best I've ever seen it, the plaster not so much with the stains...)

You can see in picture 1 the scale/flaking that is accumulating (which seem to be limited to a specific area); picture 2 shows the grit that is being captured by the Polaris; picture 3 is an example of the staining that does not brush off.

We did see what I believe was calcium scaling at the end of last summer (ie, raised nodules formed in the plaster) which seem to be gone now.

I also converted to a SWG this year (which is working well), not sure if this is a factor or not...

Thanks for reading and any help with a diagnosis/plan for remediation is welcome.


Picture 1
Pool Steps.PNG
Picture 2
Picture 3


Gold Supporter
May 16, 2010
Chapel Hill, NC
I don't think its anything to do with the SWG (and I'm not sure it's plaster "failure" from your description). Try some chlorine granules on the stain - if that get rid of it, then it's organic. If not, try some ascorbic acid or citric acid granules - if that gets rid of it, then it's metal staining. You may have to drain the the water down below the stain to clean it off if it's really stubborn (scrubbing with chlorine granules or acid granules).