Disappearing chlorine

[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.