really algae revisited

Algae problems in swimming pool water.
Green (cloudy) water or slimy pool walls.
Black algae. Mustard algae. Pink or white pool mold.

really algae revisited

Postby dalehileman » Thu 26 Aug, 2010 11:23

Though an Internet glitch of algorithm I by chance intercepted the following conversation pertinent to the greenish tint of recent interest so of course the participants shall remain anonymous. Evidently the "******" flags each response

.......was out of town last week and came home to a green pool (could not see the bottom at all). It was totally clear and blue after shocking with plain chlorine/bleach and keeping it at shock level for 3 days.

*****That symptom has happened to us also although we had evidently never been able to kill it all since the best we could accomplish was a greenish blue leading me to conclude that the tint wasn't algae after all but the natural color of our local water. But I was wrong as you shall see

Do the night test, if it is algae, let me know the size of your pool, your chlorine level, and your CYA level. I will figure out what your shock level is.

*********35,0000 gallons, non-SWG. Using exclusively tabs and a supermarket algi-clari as I had mentioned we had been unable to increase the Cl level above about 1 ppm until just recently. At a CYA of 60 I believe we should be maintaining it at 5 ppm though I'm not sure about the shock level

***********Very hesitant to use liquid or bleach in desperation we took a specimen to our friendly local Bill's Pool & Spa who then sold us 16 lb of Na dichlor shock/sanitizer which we then tossed in notwithstanding repeated warnings from all quarters that it might increase our CYA

****The results were astounding but not at first: For about a minute or so I was horrified when the water turned even more greenish with a dark brown cast but then in a short time it began to clear up until within just a few more minutes became clearer and bluer than I can remember over the past 13 years —even though a quick Cl measurement showed it at only about 3 ppm. No doubt eventually the CYA will build up but we intend to cope by replacing the water every 2 or 3 years


really algae revisited

Postby Blazing » Sat 28 Aug, 2010 15:48

I assume that by CyA levels that you are worried about, that you mean you are worried about the cyanuric acid, or chlorine stabilizer reading being too high. As a pool service and spa technician in the Phoenix Arizona area, I can tell you that any pool that has less than a 100 PPM cyanuric acid level will not hold a chlorine reading in our area. The pools that I have maintained for over 28 years have NEVER seen a negative effect from having too high a stabilizer reading, while those with lower readings are always struggling to stay free from algae, and maintain any chlorine reading.

So far, I can see why the chemical industry would want you to maintain less of a level. They get you to but 3-4 times the amount of sanitizer, and probably 3-4 times the amount of chemicals to clear up your water after the levels drop too low. Keep in mind that our hardness levels start at 650 parts per million right out of the tap, and usually are over 1000 ppm after a year, so almost all pools really need draining every year, and all pools within 2 years.

Again, my environment is different than that of most of the country, but I speak with almost 30 years of personal experience, maintaining over 50 pools a week, and training other pool men to maintain crystal clear pools year after year.
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really algae revisited

Postby chem geek » Sat 28 Aug, 2010 22:30

On your website you describe how you recommend 3 ppm FC with 100 ppm CYA, but you use Trichlor pucks so that will increase the CYA level unless there is significant water dilution. You recommend completely replacing the water every 2 years for pools with DE/sand filters and every year for pools with cartridge filters. The CH is high in the fill water of many of your pools and with evaporation and refill from the hot weather and dry air in Arizona, the CH and TA in the fill water will get added to the pool. However, this is not the situation in many pools around the country.

Look at the tens of thousands of users including pool services servicing hundreds or even thousands of pools on The PoolForum and on Trouble Free Pool who would disagree with your assessment that high Cyanuric Acid (CYA) levels don't lead to any problems such as algae. Obviously it depends on the Free Chlorine (FC) level in the pool since the FC/CYA ratio is proportional to the amount of algae-killing active chlorine (hypochlorous acid) that is in the water.

Over and over and over again pool owners report getting algae in their pools when the FC is too low relative to the CYA level. Not everyone has a problem because some use supplemental algaecides or phosphate removers that sometimes work well, and weekly shocking can delay the day of reckoning, but many do have problems. When they come to The Pool Forum or Trouble Free Pool, they start to maintain an appropriate FC that in manually dosed pools is at least 7.5% of the CYA level and in saltwater chlorine generator pools is at least around 5% of the CYA level and algae is killed by chlorine faster than it can reproduce. They then don't need to use algaecides, phosphate removers, clarifiers, flocculants, or even weekly shocking.

The science behind the chlorine/CYA relationship has been known since at least 1974 as described in this paper.

Yes, in Arizona and places with a lot of intense sun one should have a higher CYA level to help chlorine last longer, but your situation is different anyway since you have hard water with a lot of evaporation and refill that will increase CH (and probably TA as well) so do a lot of drain/refill anyway. That helps keep CYA in check. Other parts of the country don't work that way. A pool with a cover and a cartridge filter and that isn't winterized may have CYA build up significantly if stabilized is the sole source of chlorine since there is very little water dilution in this case.

The following are chemical facts:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.

There is a lot of good information on managing a pool easily and inexpensively in the Pool School
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really algae revisited

Postby duraleigh » Sun 29 Aug, 2010 09:43


It is impossible to ever "hold" a chlorine level (except at night in a sterile pool). Chlorine is continuously (24/7/365) consumed by UV rays from the sun and secondly, from organics that enter the pool.

If you are unable to maintain a residual chlorine level in a pool with less than 100 CYA, it is not lack of CYA but, rather inadequate chlorine. In short, the chlorine is being used up by either sunlight or organics and simply needs to be replenished.

As chem geek stated, thousands of pools across the country, including Arizona, are being maintained very succesfully by understanding the FC/CYA relationship and understanding the consumability of chlorine.
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