Getting Tight

After resetting the EC to 1.0 its went to 1.2 then stayed there consistently until the tank needed refilled. I noticed a couple of plants had developed a little nute burn so I lowered the EC again to 0.8 which went up to 1.0 and stayed steady. Everything seems to be booming this, even the 3 smaller ones seem to be picking up pace. I suspect these 3 are around a week behind the others as they are just beginning to display preflowers. The bungie at the back of the tent is 60cm from the top of the pots.