leaves have been turning gold
 

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

90 degrees is to hot and until you get that into the 70's range everything else you do is pointless.
Because it's so hot in your room your plants absorbed most of that solution to stay alive so I don't think it was from evaporation.
I found out years ago that every grow room that I built for clients I had to add an air-conditioner to control heat. Something most grow stores don't ever mention when they sell you all that expensive hydro equipment.
As for your nutrient strength and evaporation question I will have to check my books and get back to you.
It is always a good idea to flush your system periodically to remove fertilizing salts.