I should have read more... 5 ml per liter in my opinion is too high. I'd bring it back to 2-3 until you stabilize. Also, if Ssdivin is correct, also way too high. In soilless mix, I try to have the nutrient solution and water 6.0 - 6.2, which seems to work. Also why I'd recommend on your next grow you go with this.. When you're not able to measure the strength and pH of the nutrient solution, it's best to error on the light side. If you can afford the cost, a meter that measures pH, PPM, uS, is a very good investment. Just make sure you keep it calibrated. Recently I had a nutrient lockout problem and followed the same steps I recommend.. whala! about a week later things were looking better. I'd neglected to measure/adjust pH during the week (after initially setting it) and it was creeping up, which ended up in the problem I had, low K. Good luck, Farmer.