Do I need to Shock to get rid of Black Algae - or is brushing enough?

[CountryBumkin]

Thanks for your help.

I didn't measure the CC, so I will do that and report back (I have Ben's test kit).

Since the pool is a SWG, I don't pay much attention to how much Chlorine is going in or what the demand is. I just "adjust" the SWG so that I have chlorine in the pool (it's set at 30% now, and I run the filter/SWG 8 hours a day).

My pool is not screened, so it gets direct FL sun, and the water temp this time of year is around 90 degrees, and I get a lot of afternoon rain. So it's a pretty tough environment for a pool. But oddly, even with all the rain, I can't seem to get the CYA under 90 (over the past couple of years).

The problem started because I failed to pay attention to the SWG (the "red" light was on due to low salt, and I didn't notice it until I saw the all green algae in the pool) after I cleared up the green algae on the sides, I was left with the black spots on the bottom and steps.

[swimdaddy]

I was just in Miami for a week, beautiful, monumentally humid!

Your CYA won't drop unless you 1)drain and refill 2) have a very big algae bloom (like what happens when we northerners winterize the pool and things go very bad) 3) you have a pool party for a LOT of kids and they splash half the pool water out (this one happens to me). Evaporation won't do it.

That being said, 90 ppm is not bad, and with all the sun you get it may be a better that high.