Watering with tap water

tap water doesn't contain enough chlorine to cause a problem 99% of the time... so, culd be a lot of wasted effort. the stones will help keep it agitated and prevent stagnation. Also, if your local water uses "Chloramine" it does not evaporate quickly as chorine does. 24-48hours won't do anything in this context but waste your time. Sunlight will break down chlroine VERY fast -- ask any pool owner. If it is chlorine, set it out on deck in sunlight for a few hours... probably enough. Again, chloamine you won't be able to get rid off without a filter of some sort.. probably an RO system to do it effectively. my suggestion... take the easy path this time.. use straight tap and if you don't see any bonzing it's not hurting the plant in any way that matters much... indiscernable differences are not worth the effort.