It doesn't look good. I am thinking bacterial leaf spot. Sometimes disease can come from seeds.

I would probably discard the plants, sterilize everything with peroxide, and start over with different seeds.

I agree with the comments from Cole Robbie, it is best to start all over again. I do not know the method you are growing eg Still nutrient system, drip or flood and drain system. please let us know what system you are using.
I have cheated and attached a PH and Ec chart if you dont have one already.It looks as though you are growing under fluoro lights, or LED lighting which I use for seedlings but find the mature plants need more light.
http://www.homehydrosystems.com/ph_tds_ppm/ph_vegetables_page.html

Here is a link that might be useful: PH and EC levels

If your nutrient and ph are right I agree with the pull sterilize and start again. Once it's in the system not much other way to get rid of it.

Just as a matter of interest Rio Grande, what method are these growing in
1. Still solution ( Kratky method)
2. or recirculating system
The reason I mention this , is if the method is the still solution method, the roots should not be fully immersed in the nutrient solution as this will surely drown the plant , a slow painful death to the plant.