most likely not. the chlorine will off gas in about 24 hours from the water, it won't permeate the substrate. to keep your substrate less moist, fill the water level to about an inch below the false bottom. egg crate has a tendency to wick moisture up into the substrate, causing a bog condition.

if you do not have dechlorinator, you can fill bottles of water up and let them sit for about 24-48 hours to allow the chlorine and chloramine to off gas, then it will be safe to use.