Black [algae] Monster

suhlhorn · Jul 9, 2012

I've been a loyal follower of the BBB method since I converted my pool to SWG last year. Since then, I have had very few problems and when they did pop up, I was able to squash them quickly. But, over the past 4-5 years (since moving in) I have had an on-again off-again fight with black algae. Normally, they are small spots and can be knocked out with shock and a brush, but this year, it has exploded. I shocked it about 2 weeks ago, and it knocked the algae back, but now it has come back with a vengeance.

Here's the data:
CYA 45 (I know it needs to be higher. We got so much rain!!!)
pH 8.0 (We were out for a week and it drifted up.)
TA 70
CH 275
FC 3.0
CC 0.0
Clear Water, no mustard algae ever!

I will post an OCLT in the morning, but I don't expect anything since my CC is 0.00000000.

Two questions:
1) If I shock again, how long should I maintain the shock level to kill this stuff?!?!

2) Which levels should I adjust before I start shocking?

Thanks-
-stephen

duraleigh · Jul 9, 2012

1. Lower your pH down to around 7.4

2. Shock the pool not as you have been doing but by following the precise instructions in Pool School article...use mustard algae level

3. During this shock process, you must constantly brush the spots of algae with a steel brush....removing as much as you can. This let's the chlorine get down into the black algae spots and do a better job killing it.

4. Once the shock process is complete and the algae is no longer visible, I would elevate the chlorine to maybe 20% higher than the normal high end and keep it there the rest of the swim season

suhlhorn · Jul 10, 2012

Thanks-

Just a follow up... OCLT is 0.

More questions of course:
1) Why is the OCLT 0 if the black algae is actively growing? Does black algae not consume FC?
2) How bad is the "spot out" black algae treatment (trichlor)?

Thanks-
-stephen

duraleigh · Jul 10, 2012

More questions of course:
1) Why is the OCLT 0 if the black algae is actively growing? Does black algae not consume FC? I don't know. I could make several guesses but the point is you have algae and need chlorine to get rid of it.

2) How bad is the "spot out" black algae treatment (trichlor)? Probably not bad at all but it's still just tri-chlor (BBB teaches there are no "Magic bullets" and you will probably spend some money on something that may or may not work and will sidetrack you from defeating black algae the correct way.....it's not easy and will take diligence on your part to keep it from returning as it has done before.

suhlhorn · Jul 10, 2012

Fair enough.
Thanks!
-stephen

chem geek · Jul 10, 2012

Once black algae is established, it may not consume very much chlorine because it forms an external waxy layer that is resistant to chlorine. Once chlorine has saturated that outer layer, it won't consume much more. That's why you have to scrape off such "heads" of the algae to expose the depths to chlorine. I suppose that if you scraped all the black algae in the pool, that then you might find more chlorine loss but it depends on how much algae you've got.

Anyway, that's why our criteria for shocking doesn't just stop with the overnight chlorine loss test but includes a combined chlorine check and a visible test for cloudiness or algae.

jule · Jul 10, 2012

This is part of an article I found about various types of algae with the link to the source. Might be helpful?

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from the poolcenter.com:
Black Algae:

Perhaps the most aggravating strain of algae, it can be extremely difficult to eradicate completely. This is not entirely accurate, but the difficulty in removing it fully is due to the strong roots and protective layers over top of the black algae plant. Black algae will appear as dark black or blue/green spots, usually the size of a pencil eraser tip. Their roots extend into the plaster or tile grout, and unless the roots are destroyed completely, a new head will grow back in the same place. The heads also contain protective layers to keep cell destroying chemicals from entering the organism. Like yellow algae, black strains can bloom even in the presence of normal sanitizing levels and proper filtration. I was once told that this form of algae commonly enters a pool inside the swimsuit of a person who's recently been to the ocean.

http://www.poolcenter.com/algae.htm
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