pits and red algae

[hotshoe]

My gunite pool has pits in the plaster averaging 1" in dia. now in these pits I find what appears to be red algae. Have never seen this before. The water is sparkling clear. Regular additions of algacide and a correct chlorine level don't seem to help. shock doesn't help. the red can be scrubbed off with a wire brush, but keeps coming back. Any ideas?

I'm new here, have lurked for a year or two, but this is really the first problem I've had with the pool since I moved in 3 years ago.
thanks in advance,

Chris

[Watermom]

I really don't know what to advise you about your problem but hopefully someone will be along who can. Just wanted to say welcome to the Pool Forum!

[PoolDoc]

Can you send pictures to poolforum AT gmail DOT com? That would help.

Is the red stuff attached, or like loose dirt or powder? Algae would be attached.

Does putting chlorine powder or a chlorine tab ON one of the spots bleach it out? If it's algae, it will after an hour.

[hotshoe]

good thought on the chlorine tab to bleach it out. I will try to take some photos this weekend. I was not brought into the problem until it was a big mess. Lots of algaecide has been used, enough to kill the chlorine, which in turn was shocked to bring that up, which lowered the pH to a frighting level. All is in balance now, and still plenty of algaecide in the water.

I was told the pits/craters came for a long time ago using the wrong algaecide, copper based I think. In my last 3 years with the pool, nothing like this has happened. Guess I'm due, eh?

[PoolDoc]

Copper doesn't cause pits. Stains, maybe. No pits.

Low pH (acid) causes pits. So do various type of surface defects.

[hotshoe]

These pits were there when I moved in, and that's what I was told. Didn't make sense to me either. I did put a chlorine tab on a brite red spot, and indeed overnight it bleached it out. Now that the pH is correct, and I added 20# of stabilizer, do you think a bunch of shock and chlorine tabs in the skimmers/pump basket might get rid of the red? In another thread I was told it is not algae, but a bacteria. the pool is approx 44,000 gal. Again the water is crystal clear, but the red spots are ugly. I have been informed (you know, told) to get rid of them pronto.