Quote Originally Posted by smallpooldad View Post
One interesting thing is starting to happen. Had some grey/black stain streaks in the plaster, which I have tried to get rid of with both the ascorbic acid method and high chlorine (30 ppm) methods, neither of which worked. Well these stains seem to be slowly dissolving away with a combination of Algaecide 60 and Chlorine (held at 8 at nighttime), the Borax has definitely speeded this process, not sure why.
It sounds like the grey/black streaks are/were algae. Borax will inhibit as well as kill certain forms of algae so that is probably why it is helping along with the algaecide (polyquat 60%). If the gray/black stain seems powdery, then you may have the infamous mustard/yellow algae that is very hard-to-kill. Since the ascorbic acid didn't get rid of it, it was probably not a metal stain, but the high chlorine of 30 ppm would normally get rid of even mustard/yellow algae unless your CYA was high. Do you recall your CYA level when you were at 30 ppm chlorine? If it was 50 ppm or above, then you would need an even higher chlorine level to kill mustard/yellow algae. A 70 ppm CYA level would require at least 46 ppm FC, for example.

I really want to determine if this stuff was mustard/yellow algae because if the Borax is truly that effective in killing it, then this is yet one more reason for people to use 50 ppm Borax in their pools. Several people battle this mustard/yellow algae every year even with Ben's recommended chlorine levels so if Borax can avoid this battle, then that would be great news.

Richard