Hello to all, this is my first post so I hope I got all the details right. I'm currently growing 2 plants, the one on the left is a Critical+ feminised and the one on the right is a Blue Widow feminised. The critical is one week older then the widow, that's why it's bigger, I think it's almost 3 weeks old (from seed, not clone). I started getting yellow tips a while ago, at first I thought it was the amount of nutes so I cut them in half, but the problem is still going. After that I thought it was a salt buildup on the roots or pellets so I flushed the plant with 1 galon of water, which also didn't help and the burn is still expanding. The temperature is never over 25 Celsius (77 Fahrenheit). I'm running out of options now. The weird thing is that the blue widow is not showing any symptoms, it's perfectly healthy and they share the nutes/light/temperature. I always check the PH and make sure that it stays between 5.5 and 6.3 I'm running them on a 600W HPS light, about 40 inches away for now on an 18/6 cycle. The thing is that it looks and feels healthy other than the burn, but clearly something is wrong, the first sets of leaves are almost completely burned (as you can see in the photos) I apologize for the long post but I really am desperate. Thank you guys!