Pouring slowly in front of a return away from the edge (as far as you can reasonably stretch) will not concentrate enough chlorine to cause a problem. Another alternative that you can do is to take a large bucket of pool water and put some of the chlorine in it to pre-dilute it before adding it back to the pool, but I really think that's overkill.
If you always poured the chlorine in the same place and the tear/hole was in that place (especially if there was no return in that area), then that might be a valid correlation.
Much more likely is that the sun degraded the vinyl. UV radiation certainly breaks down the coloring in vinyl so it could also, over time, break down the structural components as well. This link is one of many that talks about this.
Richard
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