my tap water is heavily clorinated. when i do water changes, i use prime, but it still scares me knowing i'm dumping all those chemicals in there along with the water. i have a bunch of empty gallon jugs (that had drinking water in them). if i fill them up with tap water and let them sit in my garage, until my next water change (once a week), whould the clorine be gone? should i cap the jugs or leave the tops off? would i still need to use prime?