I do want to remind people that adding concentrated chemicals to a pool, especially one with a vinyl liner and no floor drain, should be done slowly over a return flow with the pump running. For chlorine, but not for acid, you can also add it slowly into the skimmer (again with the pump running) especially if you can set your filter to recirculate to bypass it. Also, when adding chlorine over a return flow, lightly brush the side and bottom where you add it so that it gets thoroughly mixed.
Adding bleach or chlorinating liquid quickly in one place can have it settle to the bottom of the pool since it is denser than water. Same is true for Cal-Hypo. Even Dichlor doesn't fully dissolve completely right away. Once any of these chemicals fully dissolve and mix, then they no longer settle and are identical in their chlorine effects (I'm ignoring the effects from increasing CYA from Trichlor and Dichlor). Trichlor pucks in a floating feeder that parks itself in one place at the side of the pool is far more damaging due to the high acidity (low pH).
There are quite a few PBs I've communicated with who swear that bleach destroys vinyl (making it paper thin), but after talking them through what their customers were doing it became pretty clear that they were just dumping chlorine quickly in one place without any mixing. When they used Cal-Hypo, they were told to premix it in a bucket of water to avoid it settling to the bottom undissolved. Like many of these myths "bleach harms vinyl" there is an element of truth, but its not the whole truth and oftentimes, as in this case, the problems can be prevented.
Richard
