1st grow purple lemonade

Start of week 4. 2 of the 3 ladies have grown quite a bit in past 6 days. The 1 smaller one has seemed to have stopped growing. Leaves are very dark green and starting to curl. I think it may be nitrogen toxicity so yesterday i flushed all three plants with straight water at a PH of 6. Started LST on the 2 stronger ones, which has exposed new growth sites over past 4 days. I do feel the plants should be bigger for day 21 but not sure, its hard to tell as the Lst has they pretty flat to the soil. Any suggestions would be great!