6% chlorine shelf life extension

[kippy313]

hello. I tried researching my specific question but to no avail. I've been using the site to get my pool in good shape, and have had great success. I try to do things as economically tight as possible. We'll be heading up to the San Jose area for a year, and I'm trying to add 6% chlorine automatically. I've come up with a simple outdoor 120V timer, and a small submersible fountain pump, (~1gal/min). I know heat and sun and time degrades chlorine. I'm thinking of putting the storage container inside a larger container and packing with dirt/soil in the space between the two containers, and periodically wetting the soil. i want to put this setup in a shaded area all in an attempt to keep the chlorine as cool as possible outdoors. I'd like to be able to go 30 days between refills at ~ 1/2 gal every other day. (7.5 gal/month) so my questions are: does sun degrade chlorine more than heat? will making the container opaque and standalone do just as fine? does diluting the chlorine with tap water make it last longer? will 6% chlorine damage the sub pump? (metal 4" cylindrical outdoor fountain pump).

thanks for any and all detailed input. And lay it all on me. I was an engineer in a past life. I can hack it, lol.

kippy
Southern Cal
see sig for pool specs

 

[chem geek]

(answered in a PM I got with the same info, but you didn't look at it yet)

kippy,

UV from sunlight is the absolute worst so having the container be completely opaque is the most important, or otherwise having it in a completely shaded area would also work.

Temperature and concentration both have an effect on half-life as shown in the table at the bottom of this link. The half-life roughly varies with the square of the concentration so using 6% bleach will last a LOT longer than 12.5% chlorinating liquid. Basically, so long as you don't have it heat up a whole lot, it should last many many months. It's only chlorinating liquid that you need to worry about getting hot -- 6% bleach degrades a lot more slowly. Certainly you will have no problem going 30 days between refills, even if you were to use chlorinating liquid. I keep my 12.5% chlorinating liquid in a shed and in a box that are both outside, but our temps don't get too high and not for too long. Also, I tend to go through 4 gallons in one month anyway.

So I wouldn't bother with the burying in soil approach. Even if you were in the "valley" in SoCal, just keeping the chlorine in well-ventilated shade should be fine. Having a white reflective surface in your storage unit with decent ventilation should make sure it doesn't get any hotter than ambient temperature. So I wouldn't have the chlorine container standalone since it could still get heated up, but would have it in a white reflective box (with screen on bottom or back for ventilation) or storage unit or shaded canopy with good ventilation.

Yes, 6% lasts a whole lot longer so you could dilute your chlorinating liquid if you wanted to, but if you really are using it up monthly then I don't think that will be necessary unless you regularly get 100ºF or higher temps (don't forget that it doesn't stay that hot at night so the temperature half-life table is overly conservative).

I don't think your fountain pump will work well with the chlorine. It's probably not designed to handled concentrated chemicals and I'm not sure how you would dose that so carefully at the high flow rates unless you had "seconds" control over timing. Usually people use a peristaltic pump for this sort of purpose as those are designed to dose chemicals accurately.

You'll need to get your TA low enough to have some pH stability since a month is a long time not checking on the pool. Also, you can significantly cut down chlorine loss by having an opaque cover on the pool and also by keeping the water cooler, so using a white reflective cover will limit heating of the pool (unless you wanted to keep it warm for your use when you visited the pool).

Richard

 

[Ohm_Boy]

I'm betting that the fountain pump will not have a very long life at all trying to pump chlorine. Sodium Hypochlorite is pretty hard on most materials, especially metals.
Let us know how it hold up.

 

[kippy313]

Thanks for the input guys. I understand and agree with what you said. Figured I test it out anyway to see if it could maintain a decent level and how long before the pump disintegrates. It's been a few weeks now, and the set up is working ok. i dilute the bleach 1:3 with water and let the pump run every m-w-f for a minute at 2gal/min. i use ~ 20gal covered black plastic container and some old metal fountain pump. the set up is under a concrete picnic table beneath a tree on an outdoor timer. no direct sunlight. I have a solar blanket on the pool. The chlorine appears to stay at or above 1-2 just before a dose is administered. pH is decent to slightly high.

There is a lot of black sediment that settles at the bottom, and the liquid is oily. The pump has some blue green scale where the outlet hose clamps on. I figured the chlorine was eating away at the black container, but it seems fine upon inspection. I do plan on using a reflective container if this continues to work ok. I flush the pump every week with water and inspect. other than the scale it's seems ok. I cant imagine the sediment is coming from the pump at all. The seals at the motor shaft and pump body appear intact. I plan on getting another container or a liner for this one to see if the liquid is indeed attacking this particular plastic. If i can get 3 months out of this junkyard setup, I have four pumps that may get me through the year.

The pool water is crystal