It kind of looks like a combo of over watering and nute burn, or possibly a potasium deficiency.

You say you're using a constant drip feeder and your ph is 6.3. Is you set up hydro or soil? If it's soil I think you're over watering them and making their nutes too strong. If it's hydro then your ph is too high. Ideally it should be 5.8 so you'd be getting nute lock out with it that high.

In either case, I suspect your nutes are too strong. Try dropping them back to around 900 PPM and if in hydro adjust your ph down to 5.8. If in soil then you need to stop the constant drip and only water them every 3-4 days and only feed them every second or third watering.