Vacation Strategy

[KurtV]

With a cya of 30, I certainly would not shock it up to 30. That would not be too good for your liner. I would probably shock it up to about 10 and then have somebody throw in some bleach every few days like Carl said.

If I'm reading it right, this chart from chemgeek says that 30 ppm FC with 30 ppm CYA is equivalent to about 3 ppm with no CYA. If that's the case, I would guess that 30 ppm FC would not hurt the liner.

[chem geek]

30 ppm FC with 30 ppm CYA is about equivalent to 5.5 ppm FC with no CYA, but I wouldn't put the FC that high since indoor pools with no CYA and with liners aren't something I've heard of. The 5.5 (instead of "about 3") is because the chart columns are disinfecting chlorine and FC level is roughly double that (at a pH of 7.5).

I think the typical "shock" level of 0.3 ppm disinfecting chlorine is more than sufficient. That is, about 12 ppm FC with 30 ppm CYA should be fine.

Richard

[KurtV]

Richard,
Thanks for correcting my error.

I'm still a bit confused as to what the HOCl (ppm Cl2) label at the top of the chart means.

[SUNNYDAYS]

If you do put poly quat in it will lower your FC. You may want to put the poly quat in 1 day or 2 before you leave then bring up the chlorine levels and shock.

[adesalvo]

Well I am back from a wonderful 10 day vacation. I had somebody add 1.4 gal of 6% bleach Sun/Tues/Thurs. I do not use a pool cover. I turned off the heater.

I left on a Friday morning with the following numbers..

FC = 10
CC = 0
pH = 7.4 - 7.6
TA = 100
CYA = 30
Temp = 86

Returned on the following Saturday night to a perfectly clear pool...sparking actually

FC = 8
CC = 0
pH = 7.8 to 8.0
CYA = 30
Temp = 105 the temp was set at 110!!

Fortunately the person adding bleach noticed the pool was getting low and added some water.

We are still in the investigating stages...but have a few leads...

[CarlD]

Sounds like your strategy was a success! Congratulations!

[chem geek]

I'm still a bit confused as to what the HOCl (ppm Cl2) label at the top of the chart means.

The "HOCl (ppm Cl2)" is the concentration of hypochlorous acid, what I've been calling "disinfecting chlorine", and the "ppm Cl2" just says that all chlorine measurements are measured in part-per-million as weight of chlorine gas (that's just the convention).

With no CYA and at a pH of 7.5, the Free Chlorine (FC) concentration is double the disinfecting chlorine (hypochlorous acid) concentration because the FC (with no CYA) measures both the hypochlorous acid (HOCl) and the hypochlorite ion (OCl-) and these are roughly equal in concentration at a pH of 7.5. So that's why I doubled the disinfecting chlorine (hypochlorous acid) concentration to get the FC level when there was no CYA.

Richard

[KurtV]

Got it; thanks.