Troubleshooting yellow in leaves?

[TruDat]

I am a newby and have some problems. Can anyone identify what I have going on with my cannabis plants?

All ideas are greatly appreciated.

 

[Jack og]

Ok we need a bit info on the grow.
Plant type (sativa, indica, hybrid)
Age
Grow control/ conditions
And pics must be with white light, the purple make it impossible to see the issue.

first glance it’s a magnesium deficiency. Get some cal mag. 1/2 dose feed it.