Is stabilizer necessary?

[BigDave]

does this mean that where Cl destroys "dirt" it leaves behind a Cl free void?

Yes; in a pool without stabilizer. If there is chlorine in the immediate vicinity bound to stabilizer then when the unbound chlorine is used up, chlorine is released by the stabilizer and is available right where it's needed.

[chem geek]

Chlorine that is bound to CYA is released very quickly where half can be released in 0.25 seconds. And yes, you are right that the bigger problems tend to be in corners or other areas where circulation is particularly poor (and yes, by surfaces I mean all solid surfaces, walls and floor). If you didn't have any CYA in the water, then the reaction rate of FC will be higher and most likely your FC level will be lower since it's so strong without CYA moderating its strength. So it's much more likely to run out (go towards zero) locally in areas of poor circulation in that case though normally in pools with higher bather load (so that there's more stuff that uses up chlorine in the water). If instead you have CYA in the water and a high enough FC to kill algae, then it is less likely to run out of chlorine locally. Think of the CYA as an active chlorine buffer holding it in reserve for when it is needed.

Now in spite of all that, the fact is that if circulation is really poor in an area, then algae can still grow because if your FC/CYA ratio is close to the algae inhibition limit in most areas of the pool but the FC drops in areas of poor circulation, then algae could grow faster than chlorine can kill it. So while the CYA buffering of chlorine helps prevent chlorine from completely running out, it doesn't necessarily help it from preventing algae completely in areas of very poor circulation. The chlorine/CYA chart guidelines are just that, guidelines. They aren't absolutes and one can readily create situations where those recommended levels won't be good enough, but for MOST pools the recommendations work very well.

[PBLsQuad450]

Thank you Both! chem geek, that is a great explanation. The sanitizing action is almost counterintuitive for me so pardon the repeat question. I am glad I have a normal pool. I also vac by hand and take a few extra minutes each time to do stair fronts, side walls and and the like. Those areas get done maybe a little less than 2X per month where the pool is vacuumed every week, at least. This is an important caveat in understanding sanitizing. Thanks again!

Paul