F21 - Fan leaves purpling. Phosphorus def? Genetics?

Ethos mandarin cookies v3, flower day 21
Growing in FFOF, following the fox farm schedule (dirty dozen + kelp me + wholly mackerel)
240w kingbrite qb (3000k+3500k w/ IR on and UV on)
pH around 6.5 each watering
Runoff pH ~6.4

I did sledgehammer flush last night (following fox farm schedule to a T as an experiment to see how it goes). Runoff was 6.4 ph after flush, brought ppm down to ~750

Night time temp low is 68°

It seems like maybe this flush stripped it of phosphorus. What do you guys think? She seems happy otherwise

are those all from seed? same strains? and could it be light stress? only appears to be mainly on the one plant

Yes, all from seed. All different strains. One is a cross of this strain x cherry berry (healthy).

I wouldn't think light stress. Light intensity/height (~22" 100%) hasn't changed in probably a week and it was fine the whole time. All other plants show no signs of light stress.

I'm only seeing the thumbnail images but that looks like a genetic thing to me or I've never seen anything like that in regards to a deficiency but I have seen it in genetics though.
A past plant used to go a deep red, pinky purple when it was maturing.

Ok. I thought maybe 3 weeks was a little too early to be changing colors