Has nothing to do with the chlorine. It keeos things sterile and never get algae or bacteria again. I've run my Rez at 90F and got roots and no slime. Tap water vs water with that is a huge difference. If you want to worry bout water temps then keep using just water, if you want no worries then use pool shock. Just my .02 cents :)
You know blacksheep as much as i hate chemicals, if it works for you i have to say you may be on to something, hear me out.
Normal optimum root zone temp according to (i knooooow i dont like to cite celebs) ed rosenthal is 72 degrees for flowering amd veg stages however i have read in several places that optimum temp for
rooting is between 75 and 85 and as anyone running a rez at that temp will tell you its near impossible to keep slime away so you are allowing your rez to maintain a better temp for rooting, even if it may be a bit harsh.