Can I put a chlorine soaked pad against my gunite wall for 5 minutes to kill black algae?

[vicmail12]

My idea: put a cinder block on the bottom, lean a 5' iron bar, anchored by the block and with a sponge pad, against an algae spot on the wall. I would enclose all but one face, maybe 4 x 4", of sponge-like pad soaked w 12% sodium hypochlorite with something to keep the chlorine from being diluted from the backside. I think it's black algae, and I think the pool is gunite, but could be plaster. When my pool was resurfaced ~10 yrs ago, they dumped a white slurry from wheelbarrows, so maybe that's the plaster over what I would guess is gunite.
Two questions:
1) Will it hurt the pool wall for 5 min, how about an hour?
2) Any ideas on what kind of sponge-like material i might use that would be compatible or at least somewhat resistant to the chlorine?

 

[ajw22]

You run the risk of bleaching color from your plaster.

Here is a better way of dealing with black algae…

You have to disrupt the black algae. If you have less than 10 spots, use a bamboo bbq skewer. If you have more, a weak pressure wash will make quick work of it. Get in the pool with a mask and snorkel and have at it. I personally dont like using a wire brush. I think it is too aggressive.

Then apply the strongest liquid chlorine to those spots as you can, either just dump it in on the surfaces and let it flow over, or get a pump sprayer. If you are lazy just dump. Sure it uses more chlorine, but you probably need to raise your level anyway.

Run FC at 20% of CYA for at least several weeks.

This is the part that sucks, run FC from then on at a minimum of 12% of CYA, 15% is better, to prevent the algae from returning.