Using Bleach to fight algae

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

Postby dstinyz » Fri 03 Aug, 2007 16:15

From what I have read it should be 40% of your CYA until it holds that level for 24 hours on its own then it should be kept at 11-11.5 of your CYA. However from my understanding if your CYA is to high( well over 50) it is hard to fight the algae and the only way it seems you can lower your CYA is by draining some water and adding new water.


Backglass
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Using Bleach to fight algae

Postby Backglass » Sat 04 Aug, 2007 08:40

dstinyz wrote:From what I have read it should be 40% of your CYA until it holds that level for 24 hours on its own then it should be kept at 11-11.5 of your CYA. However from my understanding if your CYA is to high( well over 50) it is hard to fight the algae and the only way it seems you can lower your CYA is by draining some water and adding new water.


That is correct. There is no standard because it varies, depending on your CYA level. Chemgeek has created a "best guess" chart for this but it's not in it's usual location. I am sure he will be along soon and post!
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Guest

Using Bleach to fight algae

Postby Guest » Thu 26 Mar, 2009 03:51

dstinyz wrote:From what I have read it should be 40% of your CYA until it holds that level for 24 hours on its own then it should be kept at 11-11.5 of your CYA.


Jeez :evil: my cya is around 100 at the moment but how on earth would I get chlorine up to 40 :shock:
Poolay

Using Bleach to fight algae

Postby Poolay » Thu 26 Mar, 2009 10:19

The hard science is it will differ when you consider the variables of the specific situation being treated.
Don't over-think it, over-shock it instead.
chem geek
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Using Bleach to fight algae

Postby chem geek » Thu 26 Mar, 2009 15:19

If you use a lower Free Chlorine (FC) level then it takes longer to kill the algae. If it's lower than about 5-10% of the Cyanuric Acid (CYA) level, then the algae can grow faster than the chlorine can kill it and most likely this is what happened in the first place to let the algae bloom get started. The guideline of an FC of 40% of the CYA level is for a reasonably fast kill. See Defeating Algae for more info.

When the CYA level is very high, such as 100 ppm or more, then it's usually a good idea to do a partial drain/refill to dilute the water to lower the CYA level since that's something you'll have to do eventually anyway at some point. During this time, if you want to kill some of the algae or at least keep it in check, you could use chlorine -- perhaps at 20 ppm FC if you don't want to go up higher until after you've gotten the CYA lower.

Before you add the chlorine, you should lower the pH first to around 7.2 or slightly lower. The addition of large amounts of hypochlorite sources of chlorine will raise the pH -- as the chlorine gets used up, the pH will mostly drop back down.

There are other methods of killing algae after a bloom, including using a copper-based algaecide, but they result in side effects, most notably a risk of staining especially if the pH or copper levels get high.

As for getting the chlorine level up, this is easiest to do using chlorinating liquid, though 6% unscented bleach (e.g. Clorox Regular) will work as well. One gallon of 12.5% chlorinating liquid in 10,000 gallons raises the FC by 12.5 ppm. One 3/4-gallon jug of 6% bleach in 10,000 gallons raises the FC by 4.6 ppm. So you'd be adding multiple gallons of chlorinating liquid or many jugs of bleach. If your pool is low in Calcium Hardness (CH), say because it's a vinyl pool, then you can use Cal-Hypo as a source of chlorine. Just keep in mind that for every 10 ppm FC added by Cal-Hypo, it also increases CH by 7 ppm.

See this link for how a pool gets cleared using chlorinating liquid or bleach alone. This was a person's pool upon spring opening when the pool was "let go". Larry is in the process of cleaning up a pool here so should have some more pictures showing how algae can be killed and cleared with chlorine alone. The key is maintaining a shock level of chlorine, regular brushing, constant filtration, and periodic backwashing (or filter cleaning, depending on filter type).

In the future, you have choices to make. Your CYA level probably got high because you were likely using Trichlor pucks/tabs and maybe even Dichlor granules for boosting chlorine levels. For every 10 ppm FC added by Trichlor, it also increases CYA by 6 ppm. For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm. If you want to use these stabilized chlorines, then you need to either increase the FC level as the CYA level climbs over time (which is hard to do with these products as it just accelerates the rate of CYA rise) or you need to use a supplemental algaecide (e.g. PolyQuat 60 or a phosphate remover) to prevent algae growth. Using unstabilized chlorine with a fixed amount of CYA already in the water is the least expensive way to go, but is less convenient since you need to add chlorine every day or two (unless you have a pool cover in which case you can usually add it twice a week). There are ways of automating chlorine dosing including use of a peristaltic pump or The Liquidator (but can have scaling issues) or a saltwater chlorine generator (SWG) system.

Richard
greggpica
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Using Bleach to fight algae

Postby greggpica » Sun 19 Apr, 2009 13:53

Bleach is 6.5% chlorine and liquid chlorine is 13% chlorine. Calhypo is 65% chlorine. Bleach is the same thing just not as strong
chem geek
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Using Bleach to fight algae

Postby chem geek » Sun 19 Apr, 2009 17:30

greggpica wrote:Bleach is 6.5% chlorine and liquid chlorine is 13% chlorine. Calhypo is 65% chlorine. Bleach is the same thing just not as strong

Once it is in the water, the chlorine is IDENTICAL from all sources. When you say it's "just not as strong" it would be more accurate to say "it's just not as concentrated". That means that by weight you have to use more to get the same amount of chlorine. However, bleach and chlorinating liquid are mostly water, but are also much less expensive per pound because you are getting mostly water. If you compare prices based on the amount of chlorine, then they are inexpensive and Cal-Hypo is roughly comparable while Trichlor, at 90% available chlorine, is actually more expensive due to the pH Up product you need to use to compensate for pH.

In other words, don't be fooled by the Available Chlorine percentage. See this post for a true cost comparison of chlorine sources.

Richard
Will_marx

Using Bleach to fight algae

Postby Will_marx » Fri 09 Sep, 2011 12:51

Hi Jack Sparrow,

Most of the pool professionals use the 30ppm chart found at the Taylor test kit booklet. That's the guide I use on all my pools (that's what i do for a living). Unless you already have a high level of chlorine you should aim at 30ppm. Stay away from using the pool until levels of chlorine are back to normal (1 to 5ppm). Now, this is used to treat a "green" pool. If all you have is a bit of algae on the steps or benches just brush it off and go with the 10 or 15 ppm. BTW the chlorine is more effective on lower pH (7.2) or even lower but remember to bring it back up after your treatment is done and BEFORE swimming.
I hope it helps

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