6.0 is too high PH for hydro. 5.8 is best.
Get your PH to 5.8 and hold it there.
You'll find your plants will eat more, and you'll be able to push a high EC.
My experience with TD is that she LOVES calcium. Most common deficiency I've seen with TD.
I would expect problems running PH at 6.0.
I would cut PPM's in half, run the PH at 5.6, and let it drift to 5.9 before adjusting back down again.
Give the plants a couple days to sort themselfs, and raise the PPM's slowly when your PH starts to rise again.
I've run a LOT of Think Different, and that is exactly what I'd do if it was my plants.
Peace.
Tav