Burn?

Dont worry about small burned tips, just reduce EC of the fertigation mix a bit and make sure to get 20% drain next fertigation event. Dont flush now. Consider flushing an "ultimate remedy". Flushing imposes all kind of rapid changes on your plant (fast reduction of soil EC, O2 reduction, possible temperature swings of the medium, etc.), hence its stressfull for them. Your plants look healthy and the tips are just very slightly burned. If symptoms worsen fast, then it might be nessercary to flush. And btw, I am not a plant fertigation expert at all, but given that the GHE Trio formula is complete, I would be worried adding other nutrients might cause problems, possibly leading to incorrect nutrient ratio's. I would just use the trio formula and only add other products if I know exactly what i'm doing.