How long should it take to clear black algae

[joecus]

Hello all - I need some help. I can't keep my CL levals above 10 for any length of time. Here are my numbers

fc = 2
tc = 3
ta = 90
cya = 70
ph 7.6

Every night I've been adding 2 gallons of bleach which raised my cl to about 20. Next morning, my numbers are about levels I posted above. I do have black lines near steps and corners which I assume is algae. How high and how long do I need to keep my cl levels to kill this thing. I've been using many gallons of bleach, yet no progress. Also, how high of a level is safe for swimming? Thanks a million.

One more question, I have a stand alone hot tub. My alk levels are low. All others good. How can I raise Alk only? Thanks again.

[CarlD]

OK, you are on the right track. You want to raise and keep your FC at 20. You need to test and raise FC at least 3x/day.

Meanwhile you need to brush your pool every day to knock the algae loose, and you should vacuum the pool every day as well, preferably to waste, until it's clear.

I think what's happening is the algae is using up the chlorine and you aren't getting more chlorine in the pool fast enough to prevent the algae from growing back.

Carl

[aylad]

With your CYA at 70, I wouldn't have a problem swimming with chlorine in the 10-15 ppmrange, but I'd probably wear an old suit.

To raise alk, use baking soda.

Janet

[madwil]

yep, with CYA 70, it takes a high shock level, especially with black and/or mustard algae (I think mustard is worse!)
You need to maintain the shock level as consistently as possible- during the day, as Carl said, the FC drops low enough to let the algae grow back.
add more bleach in the AM, to get the FC back up, and whenever you can during the day test and raise FC again.
As aylad said, you can swim at higher levels, even 20-25, with that level of CYA; but might be harsh on swimsuits!
You need to maintain these FC levels until your pool holds FC overnight- lose no more than 1ppm FC between sundown and sunup, without adding more chlorine!

[joecus]

Hello all, I've been keeping the CL very high yet I'm not seeing progress. How long can I expect this to last? What about raising the CL really high, (50-60 no swimming) will that resolve my problem faster>

[madwil]

not sure if I'd go that high- but super shock level is 75 for your CYA range, so it should be ok- maybe Ben or someone else will be in later to advise you...

[Watermom]

Madwil -- your post doesn't make any sense. He is wondering about taking the cl really high -- up to 50-60. You tell him you're not sure if you would go that high, but 75 should be ok.

joecus --- I did not see (unless I missed it) where you told if this was a liner pool. But, do NOT take the cl up to 75 unless Ben recommends that you do.

Are you consistently keeping the cl at shock level? If not, letting it yo-yo up and down will make it take forever and a day to clear. Are you brushing the sides and floor?

Go ahead and post another set of numbers since it has been a couple of days since you have done so. Are you running the pump 24/7? Is your filter pressure rising? How does the water look?