Plaster stain removal over winter?

[TurboMatt]

I have been working on removing stains on my plaster pool walls and floor all summer. Lots of brushing and have kept the FC above normal, around 6-10ppm. The stains have softened up some but I was hoping they would be gone by the time I had to close the pool. My plans are to close the pool in the next 2-3 weeks.

Short of draining the pool and acid washing it next spring, do I really have any options? I've scrubbed and scrubbed with a stainless plaster brush. I have verified that they are organic stains by scraping a chlorine tablet on them then waiting some time to see the stain mostly disappear.

I have read that lowering PH is very helpful to kill the organic stains. Figured this may be a good option since there will be no more swimming.

Any ideas?

Thanks

 

[Texas Splash]

Acid and/or power washing may be a quick/efficient method, but may not be feasible if your water is elevated. Something to be careful about. You mention the FC being 6-10, but I wonder if that is really a strong enough FC/CYA ratio compared to your current stabilizer level?

 

[TurboMatt]

The CYA was 40 last time I checked it. I'm fine to raise RC if that will help.

I'm curious what is more damaging to the pool if the water is full. A lower PH level or a higher FC level? As well, which would be more effective to remove the plaster stains?

 

[mikes112]

I have the same issue. I have power washed and acid washed but still there are stains. My plaster is well bonded and nice and thick so no leaks but I would hate to have to have it replasterd. Thinking of putting plaster on top of the existing plaster. Maybe first sanding the plaster to give it a texture and then rolling of some stuff like cider-crete or mixing it my self.

 

[sktn77a]

You can add ascorbic acid - that will lower the pH (high 6s/low7s) and chelate metals causing stains. Not sure I would want to leave that water in contact with the plaster all winter, though.

Have you done the chlorine puck/ascorbic acid test first to identify the stains?