Yellowing leafs mid flower NITRO ???

My PPM/PH meter is sick and at the worst time Mid flower. Anyhow Im trying to figure what my ladies are telling me without my pen for I hope only bout a week. I was thinking nitrogen but really not sure.

Here is the run down.
4 Weeks Flower all same strain

Avg PPM 1550 to 1600

PH 5.8 float to 6.1 then recalibrate. I it takes couple few days to recalibrate.

Temps lghts on 81 lght out hi 60 low 70

Technaflora nutes 3 step

Seems to be on a lot of fan leafs but only like two plants are acting like this. Not sure where it starts, top or bottom. Hope this enough to puzzle this out.

Oh after thought I have a NYCD which is the SECOND picture. What is she telling me ?? This is my week point

Thanks ladies and germs

Looks like nute lockout and burn... flush, use ph balanced water for two days and then start half nutes again. always start by adjusting ph. good luck.

Thanks for the reply.