Is Weekly Shocking Necessary?

[Jack Sparrow]

I've recently switched over to the BBB methodology and seem to be keeping a "cleaner" pool. My weekly shock is due tonight but I have no combined chlorine to speak of (possibly 0.2ppm at times).

Is it necessary to shock when your combined chlorine levels are at zero or extremely low (0.2ppm for example)?

If it's not needed, at what threshold of combined chlorine is it necessary to shock?

Thanks,
Joe

[chem geek]

No, you don't need to shock. Properly maintained outdoor pools exposed to sunlight rarely need to get shocked. If the combined chlorine level gets to 0.5 ppm or more, then you can shock the pool. In my own pool, the only time I see more than 0.2 ppm is with a heavy bather load and even then it usually goes down within one day. The same has been reported by all BBB users, but it's not a BBB thing -- it's true for any properly maintained pool (i.e. keeping sufficient chlorine levels). The sunlight exposure helps to break down combined chlorine as well.

The other time to shock would be if there is a known problem, such as an "accident", in the pool. And of course if there appears to be algae developing so that the water is turning dull looking or cloudy (and other factors have been eliminated, such as poor filtration or a high saturation index), then shock is needed. In a pool with proper FC levels relative to CYA, this virtually never happens -- but any of us can slip up now and then, forgetting to add chlorine. That's why it's best for some to use a regular algaecide as "insurance" or to use phosphate removers to control algae. Chlorine will do it, but it does take diligence (though there is The Liquidator for those that want a more automated solution and don't go the SWG route).

Richard