CYA and Lifetime of Chlorine

[chem geek]

The bucket test would be useful for determining effects that are not dependent upon depth. So if there is some sort of chemical or physical protection not yet accounted for (i.e. more than chlorinated isocyanurates), then that would be seen in such a test. A separate test with something deeper (and wider, so the sun can shine in to full depth) would be needed to test the "shield" effect from direct CYA absorption of UV. Probably a garbage can might be OK for an hour of overhead sun, but wouldn't work for more than that unless the barrel could be tilted to point towards the sun. Ideally, multiple bucket or cans with differing CYA concentrations and the same starting FC would be used at the same time -- that helps eliminate daily variations in sunlight, etc.

Another experiment that might work in a pool that already has a high CYA in it would be to turn off the circulation pump (and do not use the pool and have it be a calm windless day) and after some length of exposure to the sun, then measure the Free Chlorine level at different depths. The problem is that diffusion will tend to reduce differing concentrations, but some sort of gradient should be apparent if the "shield" effect is strong enough. If there were a measuring device (or something sensitive to UV) that could be made waterproof (e.g. inside a quartz glass container) and could measure UV, then that would be pretty definitive by measuring UV levels at various depths and various concentrations of CYA.

Remember that for a given FC level it is still expected to see the chlorine last longer at higher CYA levels. It's the specific amount of protection vs. CYA level that is what we are looking for.

Richard