Calcium Hyperchlorine Shock Dose Instantly Turned Concrete Pool Surface Black!
by Bill
The pH was 7.2 at the time. What caused this reaction? What can I do to get it right? (I added this to get rid of Black Algae, which I cannot get rid of. Any ideas on the black algae?) Thanks Thanks for the question Bill I believe this is copper sulfate stains that oxidize from a shock using calcium hypochlorite that sits directly on the copper stains. You can avoid this by using liquid chlorine as your shock. Have you had your water tested for metals and/or do you use an algaecide that has cooper it in? I'd like to have your complete chemical readings: Chlorine, CYA (cyanuric acid/stabilizer), pH, Alkalinity, Calcium Hardness, and Metals (iron and copper). It makes troubleshooting much easier and the process of clearing up your pool will go much faster. Be sure that you have black algae and not metal staining. This is very easy to do. Get a chlorine tab and put it in a sock. Put the sock directly on a black spot in the pool for about 15 - 20 minutes. Use a telescopic pole to hold it in place. If the stain fades, it's black algae. You can go to these links on how to get rid of black algae: Black Algae Is There Ever An End To The Black Algae Saga???? That Damn Black Algae Basically you'll need to shock the pool and scrub the spots with a wire brush. Black algae attaches itself to the plaster in layers. This is why it's one of the hardest to remove. It can be done, I've personally done it, but it can be a pain. If it doesn't fade, get ascorbic acid (crushed up Vitamin C) and put about 1/2 lb. in a sock and put that on the spot for 15 - 20 minutes. If that fades it's a metal/mineral staining problem and can be solved with an ascorbic acid treatment. This page has the ascorbic acid treatment: Brown Algae Won't Come Off Of A Vinyl Liner Some say to use an aluminum sulfate after plaster turns black after a shock, but this is basically a flocc, which is supposed to clear up a cloudy pool. I'm not a big fan of floccs because they're expensive and it doesn't address why the pool is cloudy is the first place. Hope this helps and good luck with your pool. Robert |
