Hello all, I'm wondering about doing a no drain acid wash due to the recent appearance of my plaster. The plaster is about 10 years old now, and a few months ago it started looking 'dirty' on the bottom. I'm not sure if it's some kind of staining, or something precipitated onto the plaster surface, or ?? I've attached some pictures, and here are some additional observations:
At the darker areas, the plaster is not as smooth as it normally was. The areas that still look white are still as smooth as ever.
The 'patterns' you see have been there since the first year we had the pool, but were always very smooth and were a very light gray-bluish pleasant looking color (not dark or brown-ish like now). I think it may have been due to something with the way the pool was originally plastered, but it was never unpleasant to look at until now.
If I lightly sand a spot, it does get a bit smoother, but the color does not go away. I have not tried sanding very aggressively yet in any spot, though, to see what will happen.
There have been plenty of times over the 10 year period that I've let the pH get to around 8.0, but it was always very temporary. Our fill water is quite hard, so we've always had a pretty high hardness reading for our pool water. TA has normally been between 80-100, pH normally around 7.6.
Rubbing a spot with vitamin C didn't do anything for a stained area.
In bright sunlight it's not too noticeable, but in shade...different story.
There are a couple of spots in the pool where the bottom has a regular flow of water over it (a low return in the deep end, and below the spillover spa in the shallow end), and both of these areas still look unaffected (white and smooth).
So, as I mentioned I'm thinking about trying the no drain acid wash and seeing if it will help. But first I would like to try and find out what this is before taking action. Thoughts? Or questions for me?