Check the pH of your medium (runoff; there's a sticky in problems about it that applies to dirt but has explanations) and make sure it's correct- 5.8-6.2 for hydro, 6.2-6.6 for soilless, 6.5-6.8 for dirt. That's important, and so is making sure that your medium isn't holding undesirable fertilizer residues.

But the heat will make all that stuff worse.

Can you get a picture of your hood and exhaust system? I have to step away from the 'pooter for a bit, but if you post up the setup, we can try to make it work more efficiently, and that could end up saving $$ in a/c too. Woo hoo!
stinkyattic Reviewed by stinkyattic on . yellow spots. pics yellow spots. a couple weeks old and have gotten a little worse. nutes at about 1/2 strength. ph=5.6 plants are 5 weeks and a day old. temps are high...around 90 during the day and 74 at night. running a 1000w hps with exhaust fan and portable a/c in room. need help. thanks in advance. Rating: 5