Disappearing chlorine

[arjayh]

Watermom.......I bought 4 gallons of 8.25% bleach which I thought would be enough to bring the fc up to 15, but I fell short.
At 8:45 pm on 7/09 I put the 4 gallons into the pool with the filter pump running. Then at 11:15 pm I tested and guessed the fc to be about a 9. It was a dark yellow without any tinge of orange which would suggest in the teens. I tested it again the following morning (7/10) and it was the same dark yellow ....which I guessed to be a 9. I tested it again at 3:30 pm and it was still the same 9 with ph at 7.6. Today...7/11 at 2pm it tested at 2. Does this pattern sound normal or does it appear I still have a problem? And if I shift from trichlor tabs to bleach it seems like I will be adding bleach daily. The cheap store brand bleach is $1.99 a gallon and the concentrate level is not stated on the label. I'm guessing it's about 6.0%. What do you recommend now?

[Watermom]

If you went from sundown one evening to 3:30 the next afternoon without losing any chlorine that is good. But, then it is odd that within the next 24 hour time period, you lost 7ppm. Personally, if it were my pool, I'd do the overnight test one more time.

Here is your choice. If you continue to use the trichlor tabs, your CYA will continue to climb. As a result, you'll have to run higher and higher chlorine levels to compensate for the higher CYA. Or, you can use the tabs for a little while to bring your CYA up some --- maybe try 60ppm or so --- and then switch to bleach and see if that allows you to go to adding bleach every other day instead of every day.

[arjayh]

.Watermom........I took your advice and did the overnite thing again. On

7/12 @ 7:45 pm I added six 121 oz jugs of 8.25% bleach.....
7/12 @ 10:45 pm my fc was apprx 15.

7/13 @ 6:30 am it was also at apprx 15
7/13 @ 4 pm same day it was apprx 10+..........

7/14 @ 4pm it was down to 4 (air temp was 102).

7/15 @ 1:30 pm fc was at 1.5

My first three readings of 15 - 15 & 10 were my best guess/approximations as it is difficult to be exact at levels well above 5 even though I used your chart.

My questions now are............is this a normal decline in this space of time and how can I switch to bleach if is going to require every other day attention. I may be gone for a week or two at a time. So I will have to go back to trichlor tablets to have my freedom............that is providing the tablets work which they have not been doing. I put two 3 inch tabs in each of two floaters today to see if the shock treatment allows the tabs to maintain a proper fc level hereon.

One last bit of info for you, I had been adding a product called Phos-Free to my pool. It's an organic product that eliminates phosphates from the water which is supposed lessen the risk of algae. Would appreciate your comments on all of this.

Thanks.

[BigDave]

My guess is that the variability of OTO readings is attributable to inaccuracy reading OTO off scale and changes in temp and sunlight. To make an assessment of loss rate will require a K-2006 which will also give you a better idea about the CYA.

Chlorinating with bleach really needs daily attention - you might be able to stretch that to a couple days with high CYA and high FC but a week is pretty long. Perhaps you can work out a hybrid plan using bleach daily and loading up trichlor when you're away. It would require regular CYA testing and adjusting the FC targets as CYA level climbs.

[PoolDoc]

As W-M said, OTO measurement is a rough estimate, not an accurate measurement of high chlorine levels.

Generally speaking, with CYA level < 50 ppm, treatment needs to be daily or continuous (feeder or SWCG). With CYA from 50 - 100 ppm, it can be every other day. From 100 - 150 ppm, it can be weekly, but you have to raise levels to 15 - 20% of CYA when dosing.

When the pool is running normally, chlorine levels need to be 10% of CYA. Under optimum conditions -- cool water, light load, good filtration -- you may be able to get away with 5%. Where loads are heavy (parties, or small pools), 15% is more appropriate.