Concrete pool - Black spots (Maybe Algae) ??? Need Help

[FormerBromineUser]

Here's something that Ben wrote once. "... to firmly determine what the spots are, swim down, and scrap the spot with your fingernail. If the spot IS black algae, you'll end up with a bit under your fingernail. Swim up, and smear the algae on a bit of white cardboard or the unlined side of an index card. Black algae will look almost black, but will smear dark green."

I would recommend running this test first.

[Wraypau]

Its definitely black algae. Did the fingernail test. How do I get rid of this algae.

[FormerBromineUser]

A quote from Ben:

(Get) your pH between 7.2 and 7.8, your alkalinity below 140ppm, and know what your stabilizer is, use the "Best Guess" chart... to determine the CORRECT chlorine levels for your pool.

Once you've done all that, adjust chlorine to shock levels AND use your brush. Continue doing so (chlorine AND brushing) for 1 week AFTER all visible algae is gone.

Then, make sure you MAINTAIN adequate chlorine levels for your stabilizer level.

Meanwhile, if you can get some calcium hypochlorite shock, and then BRUSH the spots, followed by sprinkling them with cal hypo, that will help.

[Wraypau]

Thanks for advice. One more quick question, what is proper chlorine level?

[FormerBromineUser]

It depends on your tested CYA level. See: http://poolsolutions.com/gd/best-gue...e-chart.html#a
Read it and focus then on the Best Guess Chart.

I know you have a K- 2006 and have been around the block. So you must know that if your CYA is in the high end of the range, bump the shock level FC accordingly.

If you need help, report your CYA. We will be happy to help with mor specific recommendations!

Best wishes

[Wraypau]

I took out my 2800 psi pressure washer, put on the 15 degree tip, and pressure washed the walls. (yes, the pool was still full of water, so you just hold the tip about 1 inch fro wall) and it blew all the black algae off the wall and out of the cracks, then I shocked the hell out of the pool for about a week, and man o man, it made a huge difference.

[FormerBromineUser]

Excellent to hear!!! Woot!!!!

PoolDoc always warned that black algae is very difficult to eradicate in a plaster pool. Keep an eye out for any recurrence.