Yellow Leaf problem, plz help

Yesterday I added Plant Nutrients, and some PH balance ( ph5,5 ) to the water and gave it to my plants. today the leafs turned out like this
what did i do wrong ? and whats the problem with the plants?

my first plants didn't change any color when i added these nutrients... but this time it did...

PLZ help

heat stress not ferts

heat stress? tell me more about that? as i noticed heat rise in my roob and a sudden tiny brown spot. i give it irratic light cycles too so that could add to the stress part of it'?