chlorine level ?

[Watermom]

We don't usually suggest keeping a solar cover on while shocking. Pool needs to be able to vent and also, it might not be too good for the cover.

[chem geek]

I agree completely with Watermom -- the cover prevents a lot of the chemistry of shocking from happening. You need your pool to be able to "breathe" and sunlight also helps break down combined chlorines that will form. The downside is that you will be losing chlorine during the day from exposure to sunlight. Not much to do about that except to keep adding chlorine. That's why we talk about seeing if the FC level holds overnight since that (plus virtually no CCs) means you're done with killing algae.

As for mustard/yellow algae, this "sticky" thread talks about it. You will need a lot of chlorine to kill it. With your high 75 ppm CYA, it would take at least 40 ppm FC and you'd have to start out with a pH of 7.2 before you added the chlorine. I think that in your case your better option is to do a partial drain/refill of the pool to get the CYA down to 30 ppm since that's where it should be anyway and then you'll only need about 20 ppm FC to kill this algae.

Richard

[LazyLgrecian]

oh, didn't know about the solar cover and shock thing, thanks for the info.