My PH at tap usually runs between 8.0 - 8.2.
Normally, (this is a rough geuss, because I use a little plastic syphon tube thingy that comes with the Hydrofarm kits.) into a 20 gallon reservoir, I will put about 1/2 to 3/4's of a TEASPOON to get the water down to about 6.5 - 6.2.
That's just rough measurements because tap water can be different from different sources.... The best thing is don't assume anything, don't assume your water is 8.0 everytime.... don't assume that it will take the same amount of PH down to bring you to your mark.
Also, chlorine, some people take the worry about chlorine a little overboard. It's actually a trace element needed in very small amounts by plants and helps strengthen seedlings. (according to Jorge Cervantes)...
It's like chlorine is the LEAST of my issues. I understand with otherfolks water supplies, it can be horribly strong, but, don't let it get you to excited. If it bothers you that much, set up an outdoor rain catch for christ sakes instead of running to the store for distilled water.