leaves have been turning gold

[Russo]

hey ron i asked the question with 400 hps, the tops of the leaves have been turning a gold color and dying, I went to change the nutrient solution (it was about 3 weeks old) and i know i had about 7 gallons in there, when i drained it i only had 3 because of evaporation but do the nutrients evaporate too? if not could i have an overdose of nitrogen problem? or do you think it's just the heat from the light? I have i thermometer in there, and it's been getting about 90 degrees alot more than the 72 you suggest dim. im thinking of taking the solution out, and running plain water for a couple of days? good idea? thanks ron