Tenatious Black Algae in 28-year old PebbleTec Finish Pool

[Shark22]

Hello. I'm wondering if the source of my seemingly incurable black algae problem on north-facing wall and shallow-to-deep transition is the roughness of my 28-year-old PebbleTech surface and increasingly warm water temperatures in Central Florida - currently water is at 91F. I have given it multiple TFP black algae treatments over the past 3 years. The algae disappears in winter, but is already coming back in May with FC at 6 or higher and CYA at 65

The pool is 21,000 gal. It is clear and bright, with a DE filter and variable speed pump running 12 hrs/day. Clorination is by SWC, supplemented by liquid or tablets, and is maintained at 6 PPM, except when following the TFP black algae treatment routine, which I have done multiple times. It uses a robotic cleaner. Phosphates are in the 100 to 250 range. Pool gets very little use. I fully understand the TFP approach to pool chemistry and have been diligently following it for three years. I've tried various size stainless steel and other brushes (pro-tuff). I suspect they don't reach deeply enough into the aged surface. I have not tried a pressure washer. I don't currently have one, and would be interested in what sizes have been successful. Thanks for your help

 

[ajw22]

Welcome to TFP.

I have given it multiple TFP black algae treatments over the past 3 years. The algae disappears in winter, but is already coming back in May with FC at 6 or higher and CYA at 65

Exactly what are the TFP black algae treatments you have done?

Current recommendations are:

Black Algae

This guide provides a step by step procedure for eliminating black algae in your concrete or gunite pool. Read full post here.

www.troublefreepool.com

Gently scrape a sample of the suspected black algae with your fingernail and then smudge it on plain white paper. If the smudge scrapes off and is a greenish color, then it’s black algae.

For Black Algae, you will have to disrupt the surface of the algae physically. You can use a wire brush or if it is just a few spots, put on a mask and snorkel, go into the pool, and pick at it with a bamboo BBQ skewer.

If you have more than just a few spots, get in the pool with a weak pressure washer, and you can use that to blast away the BA.

After physically disrupting the BA, you should dose it with Liquid Chlorine. Get the strongest LC you can find, and if the BA is close to the edges, pour the chlorine down the side where it washes over where the BA used to be. If the BA is all over the place, you can fill a 1-gallon pump sprayer, get into the pool, and spray those spots. And yes, you can do this all underwater.

Then you must keep your FC at 20% of CYA for the next several weeks.

This is the part that sucks; run your FC on the high side in the future at a minimum of 12% of CYA; 15% is better to try and keep the black algae at bay.

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Your one-stop shop for all things TFP to include: ABCs of Water Chemistry, Recommended Chemicals/Levels, Test Kits, Troubleshooting, and much more!

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[Shark22]

I followed the TFP Black Algae treatment instructions, using the Pool Math calculator. I kept the FC elevated during a week of brushing and for a week or more thereafter. The algae retreated a little, but never disappeared until winter. Then I retreated. I was unaware of the need to run FC high forever. Is the rough surface making this more difficult?

 

[ajw22]

Is the rough surface making this more difficult?

Yes, rough surface is what gives black algae a place to stick to and hide.

That is why black algae is only a plaster pool problem.