I see it as an initial nute burn combined with either an o2 def, or P/cal def based on ph.
Do you have algae in your res or on roots? It could be that the Algae is sucking up the oxygen in you solution, should have aerators in the mix???
Or your solution is too many ppm for the plants... this would be fixed at 75% strength.
If the ph is above 6, in hydro, get her down... or and calibrate your ph meter.
the purpling and then these issues show p def... Maybe edge it over to a n-P-K (emphasis on P&K)
Then nute burn might have shocked the plant and the regular nutes are not going up... In this case I have seen 30-50% nutes for the recovery, as the nute burn causes lockout and then the plant refuses to eat after everything is set right, and they seem to like the lower ppm mixes.
Finally, does the plant have a disease or a pest problem... Root aphids, fungal gnats... these are common and microscopic and cannot be seen without a scope.
