Without pics to go along, we can only guess....

7.0 pH is too high for this method.... 5.5-5.8 is closer to where you want your pH.... If your water source is filtered, there is absolutely no way that the unadjusted ppm is zero.... You say your nute strength is at 1100ppms....what is in those ppms??? I mean, what nutes are you using to make up your recipe??? And how many ml's of each are you giving??? What size rockwool cubes you using??? How old are the plants that you are worried about???

CGI::::::