Pool Store Claim, True or False?

[billy0952]

A clerk at the local pool supply store asked me what I was using for chlorine in my AGP. I told him I was using regular Clorox bleach. He acted shocked and told me that was not good, because it would add metals and other undesirable contaminants to my water. Is there any truth to this or was it likely an attempt to sell me his products?

I do know that the active ingredient in the Clorox bleach is 8.75%. That leaves 91.75% for "other" stuff. I wonder what other stuff is in it? In reality it's probably a moot point as people have been using it for years with no ill effects that I am aware of in my short time on this forum.

Can anybody shed any light on this topic?

 

[tim5055]

False, it will add water and a minute amount of salt.

It's really just his misunderstanding of science. It was the way he was taught. Chlorine is chlorine is chlorine. A Salt Water Chlorine Generator, Bleach, dichlor (powder shock), trichlor (tabs), cal hypo all deliver the exact same chlorine chemical - its just that each of them come along with a byproduct. Some you can live with easily, like the minor amount of salt that liquid chlorine leaves behind. Some you need to monitor and regulate, like the CYA dichlor and trichlor leave behind.

 

[billy0952]

Thanks for the quick reply.

 

[chem geek]

See this post for details of the contents of the chemicals we use for the pool. The pool store employee was either blatantly lying or was ignorant. Manufacturers of chlorinating liquid and bleach absolutely positively do not add metals in their product because metals degrade sodium hypochorite faster.

As for what else is in chlorinating liquid and bleach, as noted in the post I linked to 8.25% bleach has 8.25% sodium hypochlorite (by weight) and 6.5% sodium chloride salt and less then 0.1% sodium hydroxide (lye) and the rest is just water. Clorox brand adds a very small amount of sodium polyacrylate as well.

Chlorinating liquid, bleach, and lithium hypochlorite add about twice as much salt (after accounting for chlorine usage/consumption) as Trichlor and Dichlor, but these latter two products add Cyanuric Acid (CYA) in place of half the salt. Cal-Hypo add Calcium Hardness (CH) in place of some salt. CH is normally targeted to be around 300 ppm and is a problem when it's higher at around 1000 ppm. CYA is normally targeted to be around 30-50 ppm or sometimes 80 ppm and is a problem when it's higher than that. Salt (sodium chloride), on the other hand, is not a problem until much higher levels -- saltwater chlorine generator pools use 3000 ppm salt, for example. So use of Trichlor or Dichlor products will build up CYA much more quickly than the salt buildup from using chlorinating liquid or bleach.

As shown in this post, the following chart shows how much the CYA, CH and Salt would rise after 6 months if there were 2 ppm FC per day chlorine usage and no water dilution:

........................ CYA ... CH ... Salt
Trichlor ............. 220 ..... 0 .... 295
Dichlor ............. 325 ...... 0 ... 295
Cal-Hypo ............. 0 ... 255 ... 360
Bleach* ............... 0 ...... 0 .... 595

*Bleach, chlorinating liquid, lithium hypochlorite and chlorine gas all result in no CYA, no CH and the same amount of salt.

Note that a rise in CYA of 220 ppm is much worse than a rise in CH of 255 ppm which is worse than a rise in salt of 595 ppm.

 

[billy0952]

Thanks. I read the linked posts. Much good info here.

I understand the 595 ppm buildup of salt over the six month period is not very significant compared to the buildup of the CYA and CH. I'm wondering now if it might be a good idea for me to drain most of the water at the end of the season and replace it fresh water prior to closing the pool for the winter, the idea being to try to prevent excessive buildup of salt over several years use.

I say this because I formerly used a SWG which caused my metal pool support beams to rust out over a three year period of running the salt level around the 3,000 ppm you mentioned. I'm guessing if I can keep the average salt value to significantly less than 750 ppm then the metal beams on my new pool might outlast the liner. I'm grabbing at straws here as I don't know how long a typical Intex vinyl liner might last in SW Georgia (USA). Any thoughts on this?

 

[chem geek]

I think that doing some annual or ongoing water dilution is a good idea since you won't get hard-to-oxidize organics that are soluble out of the water any other way. Also as you point out it's a way to keep the salt in check. It shouldn't take very much water dilution, however, and certainly not requiring draining most of the water. If you were to replace 1/3rd of the water, then with the example I gave the steady-state salt would go from around 1200 ppm to 1800 ppm through the season and then get diluted back to 1200 ppm. If you were to replace 1/2 of the water, then it would go from around 600 to 1200 back to 600 each cycle.

Salt isn't a problem and some people intentionally add it (even without an SWCG) because the higher salt level lets you keep your eyes open underwater longer with less stinging. This is because human tears and fluid in the eye is at around 8000 ppm salt so anything below around 5000 ppm results in enough osmotic pressure in the eye to make them bloodshot and irritated. The lower the salt level, the greater the negative effect.

The only reason I'd keep the salt on the lower side is if you had soft stone and splash-out and evaporation of pool water in a hot dry climate and you didn't want to seal the stone.