entire plant???????

about 5 out of 50 plants have turned yellow. the entire plant top to bottom. i have searched the threads and cant find where the entire thing is yellowing. i would appreciate any advice

yellow =nitrogen deficiency

yellow from bottom to top, mites...look for webs and little pieces of mite shit along with little black dots with yellow or greenish clear sides, sometimes they move real fast, sometimes they just sit and eat. Could be mites too, need more info and pics too. close up of the underside of the plants will help bunches. Can you say macro?

ru growing soil or hydro?