Suggestions?
1. Stay away from that local pool supply, that gave you copper sulfate.
2. Verify that you have black algae; I doubt that you do. Black algae forms lumps or layers, and can be scraped off with a fingernail. Swim down with a mask or goggles, scape a bit off, swim back up, and smear it on a white 3x5 card. If it's black algae, it will smear dark green. If it doesn't . . . or if you can't feel or scape it, it's black algae.
3. Consider your options: there are 3 types of black 'stains' commonly encountered in pools: black algae (only in concrete pools), copper oxide (in any pool which has been 'coppered' and then shocked!), and black fungus (only in liner pools).
NONE of these can be removed by this coming weekend! If it really is black algae, you *might* have been able to remove it IF you hadn't added copper. If it's copper oxide, removing it will be to be difficult. If it's black fungus, the only way to remove it, is to (a) drain the pool and remove the liner, (b) treat the under surface with antifungal chemicals, (c) then install a new liner.
4. Get an OTO / phenol red testkit . Your chlorine and pH levels are CRITICAL to both controlling algae AND avoiding further copper stains. Report test results here.
5. Run your filter 24/7.
By the way, fungal staining is most common when the ground under the liner is saturated. It's rare in vinyl pool on sloped ground, but not at all uncommon in pools that are on flat wet ground.
Good luck!
Bookmarks