2 q's 1...what is the wattage of your light?
2...is that your nute solution under your plants in that aquarium? If so, then you need to cover all that up with black tape 2-3 x's or something to keep the light out or else you will grow algae, algae kills roots lights cause algae...get it? in dwc there is to be no light allowed in the res, or... see above

here is how you find out how close to get your light...you acclimate the plants to light.which you have. Then you lower the light 6 inches a day monitoring the leaves reaction...until you have light (this depends on the wattage of your lamp) 6-12 inches from canopy, without burning the leaf tips...if you get to the point that you notice the leaf tips drying and pointing up or the tips brown, don't panic, just move the light back 3-6 inches and monitor leaves reaction...as the canopy rises you raise the light keeping it at the same distance throuhout your grow...

for fans you need a small oscillating fan 24/7 on your plants to strengthen their stalks..
and a stationary fan directed across the top of the canopy and under the light, blowing the heat away...this will allow you to place your light closer than you could believe, but be careful. If you don't pay attention you will burn some tips.
when I see your reply, I will advise you further if you like...