Chlorine Stability

[hamop78]

Not sure if this is the proper forum for this so if it needs moved OK

How fast will a chlorine/water mixture remain effective at poolside, closed bucket, 2 or 3 day supply?

I'm installing a peristaltic pump to inject bleach directly into the return line. The reason I'm doing this is to stop the Yo-Yo effect of adding a massive dose at night (more like the erosion feeder from days gone by). I would put the reservoir somewhere else but I want to keep the tubing as short as possible.

The pump delivers between 2.5 and 20 GPD so I will probably have to dilute the 6% 50/50 or more. The system will run in concert with the pool pump, with manual metering based on testing.

Also any thoughts about the sunlight (UV) effect on the bleach in the 1/4" white plastic tubing as it makes it way through the system. Should I shield it from the sun? How about the Reservoir??

I'm sure I will use more bleach overall ----- BUT

Any other thoughts are welcome.

[chem geek]

Even the undiluted chlorine will last quite a while if you keep sunlight away from it and try to keep the temperature down. The half-life of 10% chlorine at 77F is 220 days while at 140F it's 3.5 days. If there are contaminants in the chlorine, then it can degrade faster. A 50/50 diluted mixture that started with 6% will be 3% and the half-life even at 100F is theoretically more than 1 year so you should do just fine so long as you keep out exposure to sunlight (you most definitely should cover your reservoir to keep out the sun).

You can get some outgassing of chlorine and even if this was relatively low so that the strength didn't decrease much, chlorine gas is poisoness and a very serious oxidant that will wreck havoc with your pool equipment, so I would cover your pump with only the smallest hole necessary for bringing in air (if needed) to prevent a vacuum.

I doubt that the UV from sunlight will penetrate white piping so I think you are fine there as well.

Richard

[hamop78]

Thanks Richard,
Since this is somewhat of an experiment I will make it hard on myself and not hard wire things just yet. That means I have some wiring to do to tie it into the pool pump feeder after the timer and switch. That also means I need a neutral for 110V (for the chem pump).

I am planning to use a plain 5 gallon bucket which is the white plastic kind. The tubing is translucent rather than opaque white, So I will try to keep it under other plumbing so it doesn't get sun. With the short run (6') and considering the volume of 1/4" OD tubing, I don't look for the chlorine to be in the tubing for long enough to matter.

[chem geek]

Just so we have a real-world data point, I measured the chlorine rise in my pool after adding what is supposed to be 12.5% chlorinating liquid and the FAS-DPD measured chlorine level I got was a little less than expected (4 cups to 16,000 gallons gave an increase of 1.8 ppm instead of the expected 2.2 ppm), about equivalent to what 10.5% chlorinating liquid would do. Given the 0.2 ppm FAS-DPD error, this isn't bad and it could be higher than 10.5%. Also, the pool store where I get the chlorine isn't great about keeping the chlorine out of the sun (it's mostly out of the sun, but is in sun during part of the day) and I don't know their turnover rate.

Richard

[hamop78]

Richard,
The experiment is on. I got the peristaltic pump hooked up today and calibrated the flow rate using pool water.

At this time I am injecting a 50/50 mix of bleach and pool water at the rate of 56 oz/hour. I tested the mixture and it came out to 3.4 ppm (FAS-DPD) using the .1ml/1L well water method you helped me with.

After 4 hours, the free chlorine had gone up 2.2 ppm so I may need to back the rate off a bit. Loss to the sun before adding any chlorine was 1.8 ppm in a 4 hour period this morning. It was not very sunny this afternoon so……..

Since I used pool water to dilute the Bleach, am I correct that this might help stabilize the mixture. Pool water CYA is ~45ppm. The half-life is a whole lot longer than the reservoir supply will last. I have a 6 gallon bucket covered with white EPDM roofing material to keep out the UV.

The better half (Jakebear) will be testing during the day tomorrow to make sure things do not run amuck.

I'll keep y'all posted.

[chem geek]

Since I used pool water to dilute the Bleach, am I correct that this might help stabilize the mixture. Pool water CYA is ~45ppm.

Yes you are correct, the CYA will help prevent the chlorine in your pump source bucket from breaking down from sunlight, just in case any got in (it sounds like it won't).

[fcfrey]

Sounds like the best of both worlds ---- No pucks and semi-automatic chlorine addition just like the erosion feeders.

Where did you get the pump and SWAG cost of the system?

[hamop78]

fcfrey,
This is an experiment so it's a bit early to tell. The way I figure, it should be more accurate than the erosion chlorinator because the technology is better and close to the same price. The pump was about $200. from Grainger. other costs were an old 6 gal bucket with lid, some scrap rubber roof material, 6 ft of wire and a plug --- Oh yes --- 2 milk crates (for now to get the pump off the ground).

Installation required drilling and tapping for a 1/4" NPT injection port that came with the pump. I placed it so it was the last piece of pipe before the return jets so it doesn't go through the solar system.

Calibration of the pump is pretty tedious since you have to measure the liquid and time how long it takes to pump it at a certain RPM. I'm building data and so far I think it pumps .07 oz per half cycle (2 lobes on the pump) so if you know the RPM you can determine the feed rate (RPM X .07 X 2). I need some more time to verify the feed rates.

Like I said in an earlier post. I test the mixture in the feed reservoir by mixing .1ml of the solution in 1L of non-chlorinated water then run an FAS-DPD test on it to determine the chlorine percentage of solution being injected. Knowing all of that and the run time I should be able to calculate the outcome before testing. The next obvious step is to put a controller (Many $$$$) on the system but for now, it is the better half twisting the knob.

[chem geek]

Just so we have a real-world data point, I measured the chlorine rise in my pool after adding what is supposed to be 12.5% chlorinating liquid and the FAS-DPD measured chlorine level I got was a little less than expected (4 cups to 16,000 gallons gave an increase of 1.8 ppm instead of the expected 2.2 ppm), about equivalent to what 10.5% chlorinating liquid would do.

I've been doing more investigation about the percentages because the measurements of chlorine percentage in bleach and chlorinating liquid is not consistently specified. There is a thing called "trade %" that is generally what appears on most bottles and some MSDS forms (though other MSDS forms use weight % of sodium hypochlorite). The Trade % is essentially the available chlorine percentage as a concentration (grams/liter/10 of Chlorine gas equivalent) and since the liquid is denser than water the actual weight % of available chlorine is less (divided by) this density (because a liter of this stuff weight more than 1000 grams).

Anyway, if I use a trade % of 12.5 for my chlorine (which is what it says on the bottle), then 4 cups in 16,000 gallons would raise the chlorine by 1.95 ppm whereas I measured 1.8 so that is quite close -- meaning the loss of chlorine concentration is probably very low indeed. I've updated my spreadsheet to reflect this new understanding (though it's a minor change).

Some of the links on this old thread have some good information on this issue and on the half-life of chlorine (thanks, KurtV). I wish I had seen it earlier -- this forum has a true wealth of excellent information.

Richard

[waste]

So are you!!