First hydro grow problem

Water 66, ppm 1100, using advance nutrients, 2x 1000w HPS, co2 gen, split, A/c.

I got three plants that are kind of taking off and the rest out of the 18 are just not doing well. I have no idea why though. Any help would be great. Thinking about scraping the whole thing and starting over. Only 2 weeks into flower.

They look like they have a nitrogen deficiency. Oh and I'm watering 15min once every 4 hours

Ebb and flow

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Pics would help. Video doesn't work.