Acid should never be added to the skimmer. It is far too strong and does not get diluted enough even pouring slowly at 2 cups per minute into a 25 GPM flow in the skimmer -- I've calculated that the result is still around a pH of 1.5 which is very, very low (Muriatic Acid has a ph of -1, yes that's negative one).

As for chlorine, there is debate about that. The high pH of the chlorine makes the disinfecting chlorine upon dilution high, but not as high as one would think, though it is far higher than achieved with normal shock levels. At similar dilution rates as for the acid above, the pH will be around 9.0 and the disinfecting chlorine concentration will be equivalent to about 16 ppm FC with no CYA. For comparison, normal shock levels are equivalent to around around 0.6 ppm FC with no CYA.

The safest thing to do with both acid and chlorine is to slowly pour it in front of a return at the deep end of the pool. This allows it to mix with the largest amount of water. The key is to pour it slowly -- don't just dump it in. The flow from the return helps to disperse and mix it. Also, one should use a pool brush to brush and mix the bottom of the pool near where one pours chemicals. This is especially important with pools that don't have a floor drain (many above ground pools) as the circulation near the bottom of the pool is generally poor. Also, both acid and chlorine are denser than water so can settle at the bottom if not thoroughly mixed in the pool water.

Richard