Strange problem

[BillB]

I just noticed what looked like two bugs (round backs and yellowish) attached to the side of my pool, about a foot under the surface.
I ground them off with a pumice stone and under them was a black pit about 1/16" deep.
I couldn't get rid of the black.
I've taken good care of the pool for almost two years and haven't had a speck of algae.
These may not have been organisms. They may have been some kind of solidified bubble.
Does anyone have any idea what this may be?
Thanks

 

[kimkats]

A black pit as in a hole in your plaster (like a belly button)?

Have you tried putting a puck over them some way? Not sure how you would do that but...............worth a try.

I have NO idea what they could be.

Kim

 

[woodyp]

We talking black algae here?

 

[BillB]

We talking black algae here?

I'm not sure, at this point.
Black algae will scrape off with a wire brush (then come right back if you don't kill it).
This won't come off with anything I've tried. It's like the plaster has been burned with a torch.

 

[BillB]

A black pit as in a hole in your plaster (like a belly button)?

Have you tried putting a puck over them some way? Not sure how you would do that but...............worth a try.

I have NO idea what they could be.

Kim

Yes, a black crater in the plaster. I scrubbed it with a puck. I don't think it will help, but we'll see.

 

[BillB]

Is there any way to do a spot acid scrub under water?
It there any kind of tool made that will allow that?

 

[Patrick_B]

Is there any way to do a spot acid scrub under water?
It there any kind of tool made that will allow that?

A piece of PVC pipe. You pour some acid into it with the end of it on the spot, and it will direct it right there.

I'm not sure that will help, because I'm not sure what it is. I've asked for some input more knowledgeable than mine.

 

[kimkats]

throwing this out there---------------could it have been a rust "bubble"? How does your plaster look? How old is it?

 

[BillB]

throwing this out there---------------could it have been a rust "bubble"? How does your plaster look? How old is it?

Possibly. I don't know what a rust bubble looks like.
The plaster is 20 years old. I looks very good. It looks almost new.

 

[Patrick_B]

That crossed my mind, but sometimes plaster issues like this can be complex, or not caused by the everyday obvious reasons. I don't want to speculate though.

 

[onBalance]

As with kimkat's suggestion, and without seeing pictures, my best guess is that a "tie-wire" or rebar is rusting out. The black stuff may need chiseling out and patch with epoxy.

 

[BillB]

As with kimkat's suggestion, and without seeing pictures, my best guess is that a "tie-wire" or rebar is rusting out. The black stuff may need chiseling out and patch with epoxy.

Thank you.