I humbly disagree that tap water won't hurt your plant if you don't aerate first (leave sit out for a day or two). and just because 80% of the country doesn't use chlorine, doesn't mean you aren't in the 20% that does. Chloramine kills bacteria, Soil mediums need bacterial growth for proper plant vigor. So actually yes you will harm your plants with chloramine indirectly, by killing off your benificial bacteria in your soil.
I water when the pot becomes lightweight (due to lack of water) you can also take a finger and feel down about an inch and check it's dry, it's not so much about how much water you use, but rather how often you water. I generally try to water until I get a little run off from the bottom of the pot (I hope you have drainage holes in the bottom) Cannabis needs oxygen for the roots, so keeping the soil constantly wet will suffocate the roots.
How hot is your room during the hotest time of the day? it could also be heat stress. Your plants don't want temperatures above 90*F or so (over 100*F and you will have some pretty bad problems)