I went to 800 with one of my plant and it got a case of nitrogen toxicity. Other one loves it at 800.
Anyway, I have a "problem" with my plants. They were agressively toped, so they were slow to grow above "ground" for the first 30 days or so (too many growth sites, not enough energy for them all), but now they have almost monstruos roots and are growing like mad in all directions. The "problem" part is they drink about a liter a day each and get EC down by over 100 uS a day. On saturday I gave them fresh res with 800 and 600 uS and now they are both at 240. I wonder how far should I let them eat before giving them a fresh res. It seems that even if I gave them res change every 5 days, they would be living for a day or two on almost pure water. Perhaps I should increase nute dosage (although one plant when younger really didn't like much nutes), or perhaps get bigger buckets (curently each one is living in a 5 gal bucket with perhaps 3,8 gals of water).