How long for Cl to disappear?

[waterbear]

OTO, the reagent in the walmart kit, is NOT an accurate way to test for FC. If you can read the test in the first 2 or 3 seconds you might get an idea if the was a large enough difference in the FC and TC. The color blocks on the comparator just don't have the accuracy to measure .5 ppm difference in the levels. It MIGHT be possible with a colorimeter.To test for FC you really need a DPD or FAS-DPD test for any kind of accuracy.

As far as your second point on how long it will take the chlorine to dissapate...I don't really know but it seems that a higher concentration would dissapate at at faster rate (similar to the way that stronger concentrations of sodium hypochlorite lose strenth faster than weaker ones) because of the instability of sodium hypochlorite. It is the FC in the solution that you would be loosing so I don't thing the amount stabilized by the CYA would have much effect. That is why you need to have a higher FC level when your stabilizer level is higher...so there is an adequite amount of available FC in the water.

Like I said, I really don't know for sure but it seems that this would be the case to me.