Flushing is for salt build up when growing with chemicals. What are u trying to flush in organic? Nothing to flush... it looks like cal mag deficiency, having them in the right ratio really helps when starting up with organics. Do u grow with LEDS?
Btw I would do nothing. In doubt do nothing. I always ride out my plants with tap water no matter what.
Also, I never check the ph, use well made worm castings in ur mix and lots of worms, well made compost should be neutral.