I think I have Black Algae

[shorembo]

My pool is:
Crystalcrete
Outdoor / unscreened
17,000 gallons
Salt generator
12 years old
Hayward C1750 Cartridge filter

My problem is that for the life of my pool, I would get a few small black spots in etched holes in the concrete starting in late summer. The black stuff had was really dark green (like spinach) and didn't smear too well.

This usually went away by brushing the pool then sprinkling chlorine (originally used some Black Spot crystals then I switched over to just a regular pack of shock) and let it settle to the bottom of the pool overnight (without running the pump). The above process usually took care of things.

It seems this summer my attack is worse. I am now getting the same stuff in the tile grout around the water line. I have tried the chlorine crystal treatment a few times but it just seems to be alot worse this year.

Is there any help?

(Not that this might make a difference but I was using Jacks Magic for a number of years regulary but quit using it around two years ago).

[Watermom]

Do you have a drops-based test kit? We need some current water testing numbers. (Tell us what kit you used to get them.)

What are the ingredients in the Black Spot crystals?

[shorembo]

I have a standard 5 liquid drop based test kit....but I just went to pinch-a-penny and had them do the test since I assumed you needed some of the other tests.

Here are the numbers:
Total Chlorine = 5.0 ppm
Free Chlorine = 5.00 ppm
Combined Chlorine = 0.0 ppm
pH = 8.0
Acid Demand = 4
Total Alkalinity = 160 ppm
Calcium Hardness = 370 ppm
Stabilizer = 90 ppm
Salt = 3,500 ppm

The crystal stuff I had used was called Spot Out (a pinch a penny product). It was made up of Trichloro-s- Triazinetrone.

When I switched to the Aqua Chem shock. It was made up of:
Sodium dichloro-s-triazinetrione 63.05%
Copper (metallic / derivde from copper citrate) 0.26%
Available Chlorine 39%

BTW, I did get a little of the black/green stuff from the tile grout and smeared it on white paper. It was interesting because it did not smear too good. Basically crumbled but left a thin dark green smear on the paper.

[shorembo]

??

[BigDave]

I presume "??" is the same as "Bump".

I agree, it sounds like black algae. That seems to be tough to clean. You can search for black algae threads using this link: http://pool9.net/search/. Basically you'll need shock FC levels and regular brushing to disrupt the black algae protective coating. Don't try to shock with the SWCG - it'll shorten it's life. We recommend bleach to shock as it adds chlorine, salt, and almost nothing else.

A couple comments,
The FC of 5ppm is pretty low for CYA of 90ppm, OK with the SWCG but near the edge. This can allow algae to grow where the water doesn't move much.

pH is a bit high and TA is a bit high with CH 370. I'd bring down TA using the Acid / Aerate process described in this link: http://pool9.net/alk-step.

My comments are based on the pool store test which we do not trust. I strongly recommend you get the Taylor K-2006 test kit. You will need it to fight the algae and to control the pool. It's not available in stores. If you order it through these links http://pool9.net/tk/, PoolForum gets some coin to keep the lights on. You may also want to order the salt strips (about the only strips we recommend).

Let us know how it's going.

[CarlD]

I'd make one adjustment to BigDave's advice.

FIRST, bring your pH down to about 7.2/7.3, or even as low as 7.0, then measure your T/A again. Dropping pH from 8 to the low 7's should bring down the T/A as well.

Your target shock level for your CYA level, is 20ppm, but, personally, with black algae on a hard-sided pool, I'd go to much higher levels, as high as 40ppm, to kill that junk. But that's me.