well first off when you let tap water sit out its only to evap chemicals that are not wanted in your plants. as far as your ppm it will change when you add your nutrients after you add your nutes then you will want to adjust the ppm, and the ph balance otherwise your just gonna screw yourself and your plantsimp:
jonnychimpo Reviewed by jonnychimpo on . tap water ppm question tested some fresh tap water straight out of the faucet, ppm = 55. tried testing some tap water that has been sitting in a plastic bin for about 3 days, ppm = 75. does this make sense? shouldn't the ppm be going DOWN as chlorine and other chemicals evaporate from the water? also, considering it's city water, shouldn't the ppm be higher? read a lot of threads with people saying their water was a few hundred ppm straight out of the tap. will calmag plus be needed?? thanks! Rating: 5