I am using tap water which has been stood for 24hrs,originaly at 6.9 taken down to 5.8 and its base is 240ppm.I dont know how to test calcium levels?.Hi weedhound,I dont really know what to say about the root bound question...they are in 4" rockwool cubes and have full roam of the 3footx2foot tray,but there is lots and lots of roots in there so it could be a possibility,the plants are about 6foot tall,that said,theres not much I can do about it now as i wouldnt be able to move them without cropping and thats not an option yet.