How long for Cl to disappear?

[Watermom]

Plus, remember, even a 'clean' pool will use chlorine. You don't expect your chlorine levels to be unchanging.

[cygnusecks]

The drop kit I have from Walmart I'm not sure I trust to measure CC. You have to measure FC by dropping 5 drops of OTO, then reading within 10 seconds to get FC. Then, after 2 minutes it "fully develops" and you can read TC. Each time I've tested, the water has never "developed" more after the initial 10 second wait, so either I have no CC (which is odd; we've been using the pool and the dog gets in there constantly) or the test is bad. I'm waiting on my PS234, which I hope has a better way to measure CC.

I'm still interested in knowing whether bleach dissipates at a constant speed, given all other variables are the same. That is, will a full jug of Cl be gone in twice the time as half a jug? Or is there a level of Cl which, when reached, will tend to stay in the pool longer?

[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.

[Poolsean]

"which is odd; we've been using the pool and the dog gets in there constantly"
Ummmm, did your chlorine drop while the dog was kept out of the pool or with the dog going in every day?
One dog can consume copious amount of chlorine! However, if you've kept the dog out and your chlorine is still dropping, you have a high chlorine demand in your pool. Combined chlorine is one source, and as suggested by Brent, OTO is a terrible test kit to use for this test.