Clorox Issues

[Oaxacaquarius]

I use the dichlor/bleach method so many on this forum recommend. I am happy with it too. But, lately, I have been trying to find a store that sells unexpired Clorox, to no avail. The usual big box stores are all selling Clorox that is at least one month expired (base on the printed codes on the bottle), and I have read that the bleach in Clorox loses about 1% strength per month after the expiration date. (I am not sure if this is true and would like to hear from our member chemists.) The grocery stores around here (Arlington VA) are no better. Are there any good online sources? The pool supply places here (and many online) tell me I shouldn't even use Clorox -- see for example: http://www.olympichottub.com/hot-tubs-sauna-blog/2012/09/hot-tub-water-care-never-use-chlorox-in-your-hot-tub/

I don't believe this. But I am frustrated with not being able to find decent (unexpired), regular clorox around here. This has been going on for the past two months. Does anyone know of a good online source, or have any other tips? I have in the meantime been subtracting 1% beach strength for every 30 days past the expiration date when making calculations using the pool calculator. But I am not sure if I want to be doing this after the Clorox is a couple of months past the expiration date. I would think that the higher pH to bleach ratio by volume in the clorox will start to catch up with me and make things harder to balance.

[chem geek]

See this post for a table showing how quickly bleach and chlorinating liquid break down over time at different temperatures. It's very concentration and temperature dependent. Unless the stores are not air conditioned and are hot, then 8.25% bleach at 75ºF would be 7.67% in one month, 7.20% in two months, and 6.79% in three months. It's not a loss of 1% per month. The loss rate slows down as the bleach becomes less concentrated.

I'm going to respond to that link you gave as that person doesn't know what she is talking about. Just remember that you always want to have some CYA in the water when using bleach which is why one starts out using Dichlor first to build up some CYA.

[Oaxacaquarius]

Thank you chem geek -- this is very helpful!

[mrwrick]

I resurrected our good ol' Hot Spring Classic with solid advice from this forum. The dichlor/bleach method was instituted and now we routinely sanitize with liquid bleach from the store. But, my sister, with whom I share the tub (we transfer use of the vacation house between our families every 2 months) says she does not want to use straight bleach and prefers to use dichlor only instead as our father did years back. I have referred her to this forum, but not sure she ever went on or read any of the expert advice here. Please answer a question for me. The CYA level adds up quickly when dichlor is used in conjunction with bleach. I have read that CYA is toxic in high concentrations and only dissipates very slowly. It seems to me that if CYA remains high, then adding dichlor only adds more than will dissipate, so it creates more of a toxic level. I have also read that CYA gradually reduces the effectiveness of chlorine. Please clear these questions up for me and my sister. Thanks

[chem geek]

For every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases Cyanuric Acid (CYA) by 9 ppm. The CYA only degrades from chlorine very slowly at a rate in a hot spa of around 5 ppm per month. So using only Dichlor has the CYA build up rather quickly if you use the spa frequently.

The issue is not toxicity from CYA since you won't get it that high and you don't drink the water anyway. The issue is that CYA reduces chlorine effectiveness so at some point the FC/CYA ratio will be low enough for the water to get cloudy because chlorine won't oxidize bather waste fast enough and it could also get low enough to allow bacteria to grow and form biofilms.

Basically, the active chlorine level is proportional to the FC/CYA ratio. The FC gets used up but the CYA does not so the CYA level climbs so the FC/CYA ratio drops and you get lower and lower disinfection. In practice this means you have to change the water sooner, but your risk increases even before then.

Is there a particular reason your sister has for why she objects to the bleach? The chlorine itself is identical in the water -- the difference between Dichlor and bleach is in what else Dichlor adds, namely CYA, that bleach does not.

If she really wants to use Dichlor only, then let her. However, you may want to raise the TA level before transferring over to her or have her start over with a fresh water fill. Otherwise, the low TA when you are using bleach may get exhausted and the pH crash when she is using Dichlor unless she monitors the TA and adds baking soda. This is because for every 10 ppm FC added by Dichlor, when the chlorine is used/consumed it will drop the TA by 3.5 ppm.