i dont have an aero garden but can tell you adding rain water to your machine is prolly the culprit. rain water lacks calcium and all those other benificial minerals. also did you check the ph of the rain water before putting it in your machine? if you didnt chances are that the ph is very very low. i would ditch trying to pretreat and use rain water and use tap if you can. if you have terriable city water then use ro water treated with calmag