Looks like a nute problem....kinda blurry. Possible pest issue, but im leaning toward nutes. I see a little tip burn, looks like you over did the nutes a bit at some point in time not much though.

Looks like a hydro setup so I would feed em just water for a day then give them a new nute mix re PHed blah blah...try some cal-mag might be the ticket for ya.

:detective1: