For years our practice has been fairly simple. We lower the water to about 1/2, blow out the pipes and use some RV antifreeze. It has been perfectly successful to prevent any damage, however in the spring the pool is very stained with algae and worse actually is the staining from leaves. Our practice has been to completely drain in the spring and power wash with enough pressure to more or less rip off the paint. We then repaint for our roughly 3 month summer season. The usage is really just 3 months due to the high cost of heating and the users loose interest once the summer season is over. Before my time the group has tried covering with plastic sheeting, but I am told it did little good.
My question is roughly can we chemically prevent at least the algae and possibly the leaf staining, at least to the point where we could just clean up the surface, with lower pressure perhaps, so as to avoid repainting each season. The rubber based chlorinated paint is getting quite expensive, our pool is 66,000 gallons gunite so it requires a lot.
Here is what I am considering. Adding quite a bit of dichloro to the half filled pool, and perhaps balancing it with soda ash. The reason I am thinking soda ash balancing ph might be needed is to prevent damage to piping, although most piping is heavy black plastic I suspect the lower drain may be metal, buried under the pool of course. If adding soda ash could prevent damage it would be a cheap preventative.
If my ideas make sense does anyone have any idea of the quantity of each required.