I think you've developed nutrient or pH lock. Did you tell us the pH? What's happening is you're killing your plant by choking it out of nutes.

You need to flush it like OY said. Get some Flouro Kleen, or Final Flush, mix per directions and do that for about 3-4 days. Then lets mix up some light nutes with pH balanced water and you'll be back in business.
herbie the love bud Reviewed by herbie the love bud on . First grow Recirculating DWC this grow journal starts off at 37 days into veg. finally got the three babies into the system after a 4 day struggle with leaks they've been flushed with r/o water for 3 days. before they were flushed, i had the ppm of the reservoir up to about 450, cal-mag and GH's MaxiGrow. I noticed slight burning of the tips. Unsure if it's from high ppm, or heat stress. Decided I will reintroduce nutrients *slowly* I should only use cal-mag when i notice signs of deficiency, right? Rating: 5