black algae back again

I've had a problem with black algae in the past but this year it was back in full bloom. In the past I was able to get it under control but this time I let it go too long. I had my water tested here are the results.
10k gunite
FAC 0
TAC 0
PH 7.8
TA 90
CYA 0
CAlcium ?
Salinity 3400
Phosphates 900


I picked up some cya and added about 1 lb to the skimmer. Should I add the whole 3lbs of cya. Or should I bring it up slowly? I'll shock the pool tonight to bring up the chlorine levels. I'll have to power wash the pool to get rid of the black spots. To what levels do I need to get the chlorine to and for how long. Any help would be great. Thanks in advance. Mack51

1 lb. is only going to give you about 13ppm of CYA. 3 lbs. would take you to around 40. I think I'd wait to add the CYA. If you are fighting algae, you may be backwashing frequently and will just throw the CYA out. Shock the pool up to 15ppm and try and hold it there to try and get rid of the algae. According to Ben, black algae is REALLY hard to get rid of.

Welcome to the forum!

EDIT -- Take a look at this thread beginning with post #17. You may have to log out to be able to see it.

http://www.poolforum.com/pf2/showthr...ar-black-algae

Hi Mack;

Pressure washing is one of the most effective ways to remove visible black algae . . . but it won't remove all of it. And, it WILL come back, if you let your pool have readings like you reported (FC=0).

If you want to avoid a recurrence of *visible* black algae, you have to plan to avoid a recurrence of "FC=0" or even "FC=1 or 2". Simply put, once you've had it in a plaster pool, you should assume (usually correctly) that it is STILL there and will begin re-growing EVERY time you let the chlorine get low.

You need to read and understand the BBB page (linked in my signature) if you want to keep your black algae invisible.

Well I can't wait on the CYA as I already put it in. My chlorine levels held for over 24hrs. How long should I keep it high 15ppm. Or should I say how long until the dreaded black algae is dead. I figure once I get it squared away I'll let my chlorine generator keep it in check. I'll definitely check out the BBB page. Thanks for your replies. I'll post in a week or so.
Mack51

That's what I'm trying to tell you: there is not a point where you'll be able to say, "The black algae is dead".

You can get to, "The black algae is no longer visible, and is definitely not growing", but not to "It's dead."!

You have to hold it at shock levels (adjusted for your CYA level) AND brush it regularly, till it's no longer visible. THEN, you have to maintain good chlorine levels permanently (again, adjusted for CYA) to avoid regrowth.

Do NOT believe the pool ads that say this or that algaecide (usually containing copper) will eradicate it. I have, in the past, deliberately and heavily stained pools with copper, and then watched the black algae simply avoid the spots with the heaviest copper concentration (ie, stains).

Ben

OK I finally got my CYA up to 40 +- and my free chlorine at 13. PH is in good shape. The pool is looking very clear and clean. I still have some black spots lingering. They seem to be oblivious to any chemicals. I'm also using HTC super algae guard (dimethyl Benxyl Ammonium Chloride 30% and Dimethyl ethelbenzyl ammonium chloride 30%. I previously used some copper based algaecide from Leslie's which did absolutely nothing except make my wallet lighter. I had read somewhere in the forums to use Polyquat 60 but couldn't find any. IS this HTH stuff similar in chemical makeup to the Poly?? If this HTH garbage? If so what should I be using? And where can I find it. I'll probably hit it again with the power washer. That should break up the rest of the "black".
Thanks in advance to you all for your insight and wealth of knowledge.
mack51

Quote:

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Originally Posted by mack51

I'm also using HTC super algae guard (dimethyl Benxyl Ammonium Chloride 30% and Dimethyl ethelbenzyl ammonium chloride)

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You are using up a good bit of your chlorine with that stuff -- one destroys the other. If that's your goal, that's a good thing I guess. But if it's not your goal, you're making a mess.

Mack, one of our rules here is we don't mix and match. You don't have to take our advice, but we're not going to spend time answering questions from folks that are trying to a little of this and a little of that. You'd be better off EITHER going with your pool store advice OR with our. Trying to do both wastes your time and ours, and doesn't help your pool.

Good luck!

PoolDoc