Yes look at that link, it may give you ideas. d

From the form I see nothing that stands out. Possibly simply a flush....

How big are the plants in 4 gal containers? Chance they could be root bound?

Get a reflector for the bulb, you are wasting 50% of your light

So to summarize,itI could be magnesium/calcium def, nute lockout, or root bound. Mag/cal def is pretty noticeable and does cause central leaf issues as you describe. Regardless a moderate flush could help. Don't wash out all the buffers