Liquid Chlorine Vs. Powder - Swimming Pool Water Chemistry - Pool and Spa Forum

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Liquid Chlorine Vs. Powder


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#1 CLamb

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Posted 18 October 2009 - 05:54 AM

Our 7 year old pool had extremely high levels of cyanic acid, so we hired a pool service to help us drain the pool, refill it, and adjust the chemicals. The service told me that using powdered chlorine increases the cyanic acid, so we should only use liquid during the off season, and suppliment with a chlorine floater during the swim season. Is this true? I'm beginning to think that the pool service people will tell me one thing to baffle me and encourage me to believe that I can't maintain my pool myself and must hire them. On the other hand, every trip to Leslie's Pool supply costs $60 - $70 as they sell me chemicals I must use to adjust my pool! They never mentioned to me that the powder version might increase the cyanic acid levels.

#2 chem geek

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Posted 18 October 2009 - 10:32 AM

The following are chemical facts that are not clearly disclosed by the pool & spa industry and are independent of product concentration and of pool size.

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 at least 7 ppm.
For every 10 ppm FC added by ANY source of chlorine, it will result in at least 8 ppm added salt (chloride) as the chlorine gets used up.
In addition, chlorinating liquid, bleach and lithium hypochlorite add an additional 8 ppm salt upon addition.

So it is not exactly true that all powdered or solid forms of chlorine increase CYA. Cal-Hypo typically comes in powdered or granular form and does not increase CYA, though it does increase CH. Lithium hypochlorite will not increase either CYA nor CH, but it is VERY expensive (a comparison of the true costs of different chlorine sources accounting for required pH adjustments is here).

From the above chemical facts, one can readily compute how quickly the CYA or CH builds up. Even a pool with an unusually low daily chlorine consumption of 1 ppm FC per day (1.5 to 2 is more typical if the pool is exposed to direct sunlight) would build up chemicals quickly. If only Trichlor were used, then the CYA would increase by over 100 ppm in only 6 months if there were no water dilution. If only Dichlor were used, then the CYA would increase by over 160 ppm in that same 6 months. If only Cal-Hypo were used, then the CH would increase by at least 125 ppm. For all sources of chlorine, the salt level would climb by over 140 ppm in 6 months and for chlorinating liquid, bleach and lithium hypochlorite it would climb an additional 140 ppm so a net total of over 290 ppm salt. Again, this assumes no water dilution from splash-out, carry-out, rain overflow, backwashing or intentional partial or whole drain/refill. Note that evaporation and refill does NOT remove anything from the pool except water and results in adding to the pool whatever is in the fill water, usually CH and TA (there is no CYA in fill water). Note that in proportional terms the rate of increase of CYA is the fastest since 100 ppm CYA is high while for CH it is slower since 300 ppm CH is a typical normal value and for salt it is the slowest since 1000 ppm salt is not uncommon and saltwater chlorine generator (SWG) pools have 3000 ppm.

By the way, what was the powdered chemical you were using for chlorine regularly? It sounds like it might have been Dichlor (Leslie's Chlor Brite granular chlorine perhaps?) which should absolutely NOT be used as a regular source of chlorine unless one intentionally wants to increase the CYA level. The "chlorine floater" your pool service talks about to use during the swim season would probably have Trichlor tabs/pucks in them and that will increase the CYA level (though not as quickly as Dichlor). Trichlor (Leslie's chlorine tabs or sticks or Genesis powder) is very acidic so will also require pH Up product (sodium carbonate) to be used. As noted earlier, Cal-Hypo (Leslie's Power Powder) will increase CH levels.

Also, were you using some sort of algicide to prevent algae growth and if so, what was it? Higher CYA levels makes chlorine less effective unless you proportionately increase the Free Chlorine (FC) level so to prevent algae growth an algicide is usually required. This is because the active chlorine (hypochlorous acid) concentration that kills pathogens and inhibits or kills algae is proportional to the FC/CYA ratio. This is known science since at least 1974 as definitively determined in this paper and that has been demonstrated in other scientific papers as I describe in this post. You can maintain your own pool algae-free by initially setting the pool water chemistry parameters (including CYA and CH) correctly and then using unstabilized chlorine (10%/12.5% chlorinating liquid or 6% unscented bleach).

You can learn much more about how to properly maintain your pool by reading the Pool School. I have a 16,000 gallon pool shown here that I maintain myself costing only $17 per month in chemicals. I only add 12.5% chlorinating liquid I get from my local pool store (they reuse the bottles so it's even better than recycling) added twice a week and a small amount of Muriatic Acid added every month or two. That's it. Of course, I have an opaque electric pool cover that cuts my chlorine usage down to a little less than 1 ppm FC per day with the pool used daily for 1-2 hours and at 88F temperature so perhaps half what it might be without a cover in sunny areas. The key is to maintain an appropriate FC/CYA ratio to prevent algae growth (it's much more than enough to prevent bacterial growth) as shown in the Chlorine/CYA Chart in the Pool School. Because of my pool cover, I only add chlorine twice a week. Without a cover, you would likely need to add chlorine every day or two unless you were willing to have much wider swings in FC level (and a higher CYA level to lower chlorine loss).

If you wanted additional pH buffering, some algae prevention, and a sparkle to the water, you could also consider adding 50 ppm Borates to your pool. This is optional and described in this article in the Further Reading section of the Pool School.

Using Trichlor tabs in a floating feeder or inline chlorinator is certainly more convenient than adding chlorine every day or two, but it comes at a price. One has to manage the CYA level, usually through intentional water dilution, and one usually needs to use a supplemental algicide or phosphate remover at extra cost (even then, this doesn't always prevent algae growth completely). If you use unstabilized chlorine or otherwise manage the CYA level, you won't need an algicide and also won't need to shock the pool regularly.

Don't blame your pool service or the pool stores for not giving you this information. The chlorine manufacturers that make stabilized chlorine (Trichlor and Dichlor) and Cal-Hypo do not properly disclose the chemical facts to their distributors, sales reps, etc. nor is this information taught thoroughly in the standard NSPF CPO or APSP TECH courses that "certify" pool operators and others in the industry (I've contacted these organizations and nothing has changed). The information is also not disclosed in their marketing literature or on their labeling, with the excuse that they can't do this due to FIFRA rules enforced by the EPA even though such rules allow for factual disclosures with a quick 30-day review so long as it does not discuss dosing or make claims with regard to sanitation (i.e. the chemical facts of CYA and CH addition would be approved quickly).

Now that you have been told the truth, you can join the over 20,000 members of The PoolForum (which unfortunately does not accept new registrations) and over 10,000 members of Trouble Free Pool who manage their pools with factual knowledge and save money doing so.

Richard

#3 Sharon K

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Posted 11 January 2010 - 01:48 AM

QUOTE (CLamb @ Oct 18 2009, 06:54 AM) <{POST_SNAPBACK}>
Our 7 year old pool had extremely high levels of cyanic acid, so we hired a pool service to help us drain the pool, refill it, and adjust the chemicals. The service told me that using powdered chlorine increases the cyanic acid, so we should only use liquid during the off season, and suppliment with a chlorine floater during the swim season. Is this true? I'm beginning to think that the pool service people will tell me one thing to baffle me and encourage me to believe that I can't maintain my pool myself and must hire them. On the other hand, every trip to Leslie's Pool supply costs $60 - $70 as they sell me chemicals I must use to adjust my pool! They never mentioned to me that the powder version might increase the cyanic acid levels.


Hi !
I've just visited this forum. Happy to get acquainted with you. Thanks.

#4 Gavin

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Posted 12 January 2010 - 11:02 AM

excellent info thanks Chem Geek.

I have a pool that has a high CYA so I just add a little bleach once a week to keep the FC between 9-14 to prevent algae. my CC is 0 and I'm happy now. smile.gif

#5 chem geek

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Posted 12 January 2010 - 10:06 PM

That's great. There are other alternatives to prevent algae growth if one wants to have the high CYA and have the FC lower, such as using algaecides (PolyQuat 60 weekly) or phosphate removers, but these are extra cost and either need reapplication or have other issues. Of course, at some point you'll need to dilute the water to lower the CYA level.

#6 Gavin

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Posted 18 January 2010 - 08:43 PM

QUOTE (chem geek @ Jan 12 2010, 10:06 PM) <{POST_SNAPBACK}>
That's great. There are other alternatives to prevent algae growth if one wants to have the high CYA and have the FC lower, such as using algaecides (PolyQuat 60 weekly) or phosphate removers, but these are extra cost and either need reapplication or have other issues. Of course, at some point you'll need to dilute the water to lower the CYA level.



Yes I've been trying to get the CYA down a bit more by back washing and refill. I might in the summer supplement with a floater. definitely if CYA goes down I guess using a floater would be ok as well as some bleach. kinda a hybrid approach. will need to make sure to keep regularly supplying enough FC (6%-8% of CYA) in the pool during the summer months. Kinda want to stay away from algaecides as I hear they add copper and other stuff which could build up and cause stains.

#7 chem geek

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Posted 18 January 2010 - 11:20 PM

You are right to avoid copper (especially in a plaster pool) to avoid staining. There are algicides such as PolyQuat 60 that are fine to use, but if you rely on them then they need to be added weekly as chlorine breaks them down and they are also clarifiers so get caught in the filter as well. They are extra cost and not needed if you maintain sufficient FC/CYA, but if you want an algicide option, then PolyQuat 60 is the one to use.

#8 RetiredFuzz

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Posted 09 June 2010 - 09:04 AM

Living in Florida I maintain my in-ground pool and spa all year long - myself. We have many pool supply stores down here, the most impressive are the mom and pop stores. Leslie's tried to sell me on powdered chlorine years ago - asked about downside - I was told that there were none. I quickly found out that the powder dissipated more quickly than the liquid chlorine - and as I did my research I was told that I would need to drain the pool at least once a year when using powder. That didn't sit well with me since the cost of water down here in Florida isn't exactly cheap. I also found that every time I went to Leslie's they would take my jugs to the back to fill and once in a while you would hear a "Holy crap" back there - indicating that once again I have a hole in my jug thus having to buy another jug. I know chlorine is a corrosive (I was a Haz-Mat cop), but every time inside 30-45 days? Comon!
I'll stick to my baking powder, and muriatic acid along with my wire brush and my Hayward Vacuum - but most importantly I will without a doubt stay with my liquid chlorine!
Sometime in the future - 25, 50, 75 years hence - what will the situation be like then? By that time the Chinese will have the capability of delivery too.
"Curtis Lemay"




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