Dirt Stains on Plaster Walls - Need tips to clean

[medfordman]

Hi. There are a bunch of dirt stains on the walls of my plaster pool. Brushing doesn't seem to help (although I am going to get one of those whale tail brushes).

Can anyone recommend a good brush/cleaner that would do the trick.

I don't have any algae problems, so I really don't want to drain the pool and use an acid wash.

Thanks,
MM