Thank you guys for the input. I went to local hyro store today and checked out the tds meters. I will be getting one next week. As for the tent being too big. I have another 1000w and a 400w both vented hoods as well just afraid to use any more power. I have my setup in garage and between the a/c the lights and so fourth my bill is pretty high. I plan to section off the tent to help this problem. I will cut space in half and use one side for veg and one side to flower. I will just have to figure out how to deal with my a/c it enters on one side of tent. I will research ppm's as well. Is there a min and max range your ppm's should be in or is it different per each persons set up? As far as the RO water, I am a plumber so that's no problem but the amount of RO water I need would be a problem as the household systems I have installed would be lucky to provide enough in a week if I took water out every day. As you know they produce water very slow and waste more than they make. Is there any other filter available that will give similar results? I don't know of any that will get close to RO water available from my supply house.