vegetation leaf death with pics

I have a few types of plants and the only ones that are dying are my tomatoes.
They started dying after being transplanted to 4x4 cubes and have never recovered.
Background: 4x4 in hydroton watered once every 1-2days for15min
Of 600 ppm flora nova in 300 ppm tap water at 6.0 Ph. Under 400w mh 74f 45rh. Please and thank you for ANY advice!

MOLD....Its very bad
Do u use ppm or ph for check the water with?

well it looks like its either to hot ( air), to much nuterietns, or the ph is off, try giving them water phed at 7.
if they were mine i would stop feeding for a bit