hey there, I think you're doing great, I wouldnt add any nutes or do very many things different. What I can see is that that color change is due to temperatures not nutrient burn, so that's good news. Seems your temperatures are actually alright, so what I can see is the solution temperature you're feeding with is actually too cold. it's shocking the roots a bit and making the colors turn, so what you can do is raise the solution temperature to the optimal 21°C, and you'll be 10/10 dialed in perfectly.