Phosphorus with cal/mag deficiency?

Hey guys im growing 2 purple kush and white rhino in a rdwc. I notice a few tip burning once i started to flower so i brought the ppm down to 600s with RO water. Now i started to notice dying on the purple kush lower fan leafs and rusted spots on the mid fan leafs while the white rhino is showing no signs of stress. Just wanted to confirm with the community if it was a combination of phosphorus cal/mag deficiency. Currently on day 24 after flip to 12/12 light schedule.

What’s your res reading after a day running at 600ppm?

If your plants are feeding and reducing the ppms in your res that in turn makes the ph rise which can halt the uptake of Ca.

are You monitoring your res levels? Ph ppm/EC?

Yes I monitor it on a daily base. Notice a slight increase but nothing to big. I organally at the ph at 6.2 but drop it down to 5.8. Ppm 600/EC 1.2