Numbers = confusion

[CarlD]

Is the 30 the CYA level or the FC level? If it's the FC level, your pH may well be far lower than 7.2. If it's 7.2 when the FC is below 10ppm then it's OK. Chlorine is more effective when pH is 7.2 than 7.6. But if it's 7.2 when FC is 30, you should add Borax until you get a reading between 7.6 and 7.8, just to be safe.

Normally, what we recommend, is keep your pool at shock level continuously until you don't get a precipitous drop in FC between dusk and dawn. But shock level is determined by CYA level. However, the highest shock level we usually recommend is an FC of 25 when CYA is over 100. However, the only risk of keeping FC at 30 is you MAY bleach your liner. If it's an old liner, my feeling is Who Cares? If it's a newer one, you may want to be careful.

You will need to be persistent. It's not how much chlorine bleach you add--it's how well you can maintain the shock level. We normally recommend checking it 3x/day. Morning, noon and night. If you cannot manage the noon test, then morning, just after work, before bedtime instead. You also should vacuum to waste 1x/day and brush the pool's sides and bottom 1x/day to knock algae loose and get it and dead algae out of the pool.

[chem geek]

The Tatlor website lists no official interferences for that test but I tried the CYA test several times at 30ppm FC and got a value that was 30ppm lower than at Target FC levels.

It is possible that at high FC levels that these chlorinated isocyanurates do not precipitate with melamine in the CYA measurement test because the chlorine is where the hydrogen would be in CYA so no hydrogen bonding occurs. The CYA level could measure lower by as much as the FC level.

This is easily overcome by dechlorinating the water sample such as by using the Taylor R-0007 thiosulfate reagent or other reducing agent such as hydrogen peroxide. One would add this to the water sample before adding the melamine.

[CarlD]

Thanks for the clarification and useful "hack", Richard!