Safe to swim once below shock level. Source?


Jun 20, 2008
Wichita, KS
First off, I've been around here for a couple of years and this site is BY FAR the best place to get great info regarding pool care!

That being said, I've seen the recommendation regarding maximum safe FC levels used quite a bit - that being it is safe to swim in a pool once the FC level has dropped to below shock level. The question I have is: why? I'm curious as to whether there is evidence of harm to swimmers above that level or if it's merely a rule of thumb. I've heard of eczema sufferers whom benefit from 'bleach baths' where the FC level is, presumably, much higher than what is normally seen in a pool. So on the surface, there seems to be a bit of a conflict. So beyond the possibility of ruining a bathing suit sooner or the like, what's the harm?


TFP Expert
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May 7, 2007
Silver Spring, MD
Many people swim at far higher active disinfecting chlorine levels all the time in indoor pools, because those pools don't have any CYA in them. However, various things start going wrong. At higher active chlorine levels there is hair damage which can cause frizzy hair, or in extreme cases cause hair to break off completely. Many people report skin irritation at higher active chlorine levels. Plus, bathing suits fade and elastic fails at these higher levels. The recommendation we make, FC below shock level, includes a large safety margin below the levels at which these effects are commonly reported.

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