Extending shelf life of sodium hypochlorite

[mjmeans]

Hi.

My local pool supply store has 12.5% trade concentration of sodium hypo for $4 per gallon in 4 gallon totes. I have a SWCG and the liquid is for that occasional shock value during the summer. I use the super-chlorinate setting on my SWCG during the winter. ​

As with all things, the more you buy, generally, the better price you get. So let's consider sodium hypo 12.5%. Lots of it. This PDF https://www.oxy.com/OurBusinesses/Chemicals/Products/Documents/sodiumhypochlorite/bleach.pdf states that it can be made much more stable if it is polished through 0.5 micron filters and raised to a pH of 12-13 and in the end it should be clear. And that it should be kept at temperatures below 25 C, the colder the better, but not freezing.

My guess is that what the pool supply store sells does not meet these stability guidelines specified in that PDF since what it sells has a yellow-ish color, not completely clear (it's not cloudy, just not completely clear). So I'm guessing that there are impurities.

As for the temperature issue, a cool basement works, or a peltier-junction type wine cooler (very energy efficient) to keep them at about 13 C. Since I don't drink wine, might as well put the thing to good use.

If I can buy sodium hypo at less than half that price but I'd have to buy 32+ gallons, way more than I would use in a year, how would I go about stabilizing it and what would the cost be per gallon? If it would cost less than $64 for the materials to stabilize 32 gallons, then it would still be a bargain. Any chemists out there what to tackle this?

 

[YippeeSkippy]

Hiya Mjmeans, welcome

I don't think you're going to get much of a deal in the end by buying that much, especially for something only used occasionally. In fact, you should be using it during the winter instead of taxing your SWG unnecessarily which shortens its lifespan.

I predict that after 6 -9 months your 12% will be more like 6% which makes it kinda expensive. Walmart's cheapest bleach is 6% for $1.77 in my town. And I don't have to store it or haul it all at once.

Just something to consider.

Maddie

 

[zea3]

Maybe you can find some friends to split the shipment with instead of trying to store it all.

 

[cfherrman]

Just buy 6% and not really worry about it. Self life on 6 is over a year I believe

 

[mjmeans]

I don't think you're going to get much of a deal in the end by buying that much, especially for something only used occasionally. In fact, you should be using it during the winter instead of taxing your SWG unnecessarily which shortens its lifespan.

My pool has an in-floor rotating pop-up head cleaner so chlorinated water from the SWG is applied directly onto the surface of the pool.

I'm using AquaRite T-CELL-15 (rated for 40,000 gallons) and my pool is only about 12,000 gallons. I'm in southern AZ, so winter is virtually free of rain; the only rain with significant impact on the pool is during July-August. In the winter I run the pump (and SWG) only 4-5 hours a day and set the SWG to 30%-40%. Maybe once every other year in the winter I might need to use super-chlorinate (using the SWG super chlorinate switch) if the test results show any CC. Last winter I would only test after some event (like a tiny rain or wind storm).

At the end of Dec FC was about 4, so I dropped pH to 7.2​

and didn't even bother testing the water at all through Jan & Feb. Usually I don't see any CC except in the summer. In the summer I run the pump 8 hours a day with the SWG at 60%. I keep CYA low; currently it is 36 ppm. This maintains at least 2-3 FC year around. The pump (and SWG) are set to run only at the most direct sun portion of the day. I acid clean the cell as needed (2-3 times a year). I use slightly lower concentrations of acid to water than the manufacturer suggests to clean the cell which means it takes about 30 minutes to clean it rather than 10 minutes, but it is safer for the cell that way. Since I'm using an oversized salt cell at significantly lower than 100% utilization and for only a few hours a day, the cell has lasted a very long time. It's now been about 8 years with that cell with no signs of degraded operation. Since I'm running the pump for only 4-8 hours a day, electricity cost is also minimized. TA is 80 ppm and 4 gallons of acid to combat the pH rise from the SWG lasts me almost a year. I hardly ever have to adjust TA (I don't think I needed to adjust TA at all in the last three years). Each year there is a partial replacement of water (draining about 1,000 gallons of the water); I live in a desert and wasting water is bad. The partial replacement of water may be what is keeping TA level, year after year, but I never analyzed that. In the past I used the SWG (and sometimes powder) to shock in the summer (the only time of the year it ever really needs it). This year, I'm using sodium hypo since I don't want to increase CYA (with powder) any higher than it already is and I don't want to tax the SWG. Since lower concentrations of CYA means FC works faster, my assertion is that if I had higher CYA then the highly chlorinated water from the SWG being applied directly to the floor of the pool through the in ground cleaner pop-up heads wouldn't work as well and then I would need to run the pump and SWG longer each day (at higher cost for electricity and more wear on the salt cell) and this would also mean higher acid demand (and more cost). I think I have this set up at about maximum optimization, all things considered. I need to make adjustments only when "events" happen, like unexpected rain or wind storm or bather load, etc.
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