Okay, I *think* I understand what's going on, but want to get the thoughts of more experienced pool people.... I haven't dealt with black algae in years (after Hurricane Katrina or Gustav, I believe), but I know it when I see it and I know how hard it is to get rid of it. When I spotted the tell-tale signs two days ago, I didn't say anything; I just hoped my frequent brushing and keeping my FC at 10 ppm would take care of it.
No dice.
So, yesterday, I took extreme measures (not really that extreme) and lowered my pH to around 6 or so using muriatic acid. Before that, I bought a new wire brush and spent about an hour working on the black spots. About an hour later, I added 4 more gallons of liquid chlorine (10.5%) and called it a night. Here are my numbers right before I added the muriatic acid and chlorine, followed by my numbers just now:
Yesterday, ~7:00 PM:
pH: 7.2
FC: ~6.5
TC: ~7.5
CC: 1
TA: 110
CalH: 310
Cya: 50
Temp. 87*
Today, 1:00 PM:
pH: ~6.5
FC: 0 (!!!)
TC: .5
CC: .5
TA: 30 (!!!)
CalH: 300
Cya: 40
Temp: 85*
I know that black algae eats chlorine up like nobody's business, but quite frankly, I am shocked by today's numbers! I retested three times because I thought they were in error. Nope. My chlorine is GONE. That's AFTER adding 4 more gallons on top of a FC level of 6.5! Can black algae really go through it this quickly?? The algae looks considerably better today, but it's still there. I'll do more brushing after this current band of rain moves through.
Oh, the joys of living near the Gulf...
No dice.
So, yesterday, I took extreme measures (not really that extreme) and lowered my pH to around 6 or so using muriatic acid. Before that, I bought a new wire brush and spent about an hour working on the black spots. About an hour later, I added 4 more gallons of liquid chlorine (10.5%) and called it a night. Here are my numbers right before I added the muriatic acid and chlorine, followed by my numbers just now:
Yesterday, ~7:00 PM:
pH: 7.2
FC: ~6.5
TC: ~7.5
CC: 1
TA: 110
CalH: 310
Cya: 50
Temp. 87*
Today, 1:00 PM:
pH: ~6.5
FC: 0 (!!!)
TC: .5
CC: .5
TA: 30 (!!!)
CalH: 300
Cya: 40
Temp: 85*
I know that black algae eats chlorine up like nobody's business, but quite frankly, I am shocked by today's numbers! I retested three times because I thought they were in error. Nope. My chlorine is GONE. That's AFTER adding 4 more gallons on top of a FC level of 6.5! Can black algae really go through it this quickly?? The algae looks considerably better today, but it's still there. I'll do more brushing after this current band of rain moves through.
Oh, the joys of living near the Gulf...