Bleach cost with LQ...

[feetr2c]

Got my LQ at the beginning of the season and am finding that I need to add a gallon of 12.5% bleach every 2-3 days. At $3.99 a gallon, this translates to a 16 week seasonal cost in excess of $200 for chlorine. Does this seem high for a 13,500 gallon AGP? I gave up on the intex SWG due to the cost of replacing a dead cell every year. At this rate I could buy a new SWG every summer. I did notice that putting 50 ppm borates in my pool eliminated and crusty build up on my LQ floats.... This leaves me wondering if it would also prevent buildup on the SWG cells.

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[JasonLion]

That is a little more bleach usage than I would hope for under good conditions, though still reasonable. A well balanced pool should use around 2 ppm of chlorine per day, which is about 27 oz for your pool size, or about 65% of a gallon every three days. Usage will be higher than my prediction when it is really hot, which it has been in much of the country recently.

What is your CYA level and what FC level are you targeting in the pool?

 

[feetr2c]

My CYQ is 40 and I'm targeting 2-4 ppm

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[chem geek]

One gallon of 12.5% bleach in 13,500 gallons is 9.3 ppm FC so over 2-1/2 days that's 3.7 ppm FC per day which seems excessively high. Also note that 2 ppm FC (the low end of your target range) with 40 ppm CYA may not be enough (I'd target 3 on the low end) so maybe you've got algae growing. I'd do an overnight chlorine loss test (OCLT). If that shows significant chlorine loss, then shock the pool. If not, then perhaps you need to raise the CYA level some the pool has a lot of direct sunlight and if you do then raise the FC target as well.

 

[feetr2c]

In fact my chlorine level dropped off to nothing for a couple of days and I did see slight green. I superclhorinated to 30 ppm one eve and shut off the LQ. The next eve I was down to 8 ppm and started the LQ back up, setting the flow ball to just a titch over 2. That was last eve. Tonight, I'm still holding steady at 8 ppm. I'm almost thinking that maintaining a higher level of FAC might actually use less chlorine than trying to hold a low level.

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[chem geek]

I'm almost thinking that maintaining a higher level of FAC might actually use less chlorine than trying to hold a low level.

That almost certainly means that you were getting nascent algae growth that was using up more chlorine. A higher FC/CYA ratio will kill that off. Of course, if you go even higher in FC, then you lose more chlorine so you can find a sweet spot for your CYA level. Remember that at 40 ppm, the minimum is 3 ppm but not every pool has ideal circulation so you might need something higher, but I doubt you'll really need as much as 8 ppm. At least now without the big chlorine loss you can slowly lower it to see how things go. I suspect you'll be able to be at 4 ppm (minimum) without problems, but let us know.

 

[feetr2c]

Lesson learned.... Test it every day lol

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[feetr2c]

Another thought comes to mind......my pool is uncovered and out in open sun. Despite having CYA of 40, it would seem to me that an open pool would use more chlorine than a covered one.... Am I correct?

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[chem geek]

Absolutely. If one has a mostly opaque cover on the pool most of the time, then the only chlorine loss is from oxidation of the cover, filter (depending on type of material), metal, CYA and any organics in the pool. All of that is a function of temperature. If my pool wasn't used every day and was kept covered, it would lose around 0.7 ppm FC per day at 88ºF and less at lower temps. I figure about 0.2-0.3 ppm of that is oxidation of CYA and the rest mostly the pool cover.

In fact, you can easily tell how much you lose from sunlight vs. everything else by measuring the chlorine loss overnight when the sun is not on the pool vs. the loss when the sun is on the pool. Just scale the overnight loss to an hourly rate, then subtract that rate times sunlight hours from the loss during the day to get the loss from sunlight alone.