Brownish leave spots

Well if your growing aeroponice then your ph needs to be around 5.7. Your ph is way to high for a soiless system. Also as far as sitting your water out for a few days does it lower your ppm? My city uses chloramine. If your city uses chloramine then it doesn't do you any good to let your water sit. I know some people who use organic nutes for hydroponics but their honestly only recommend when your using soil.Your correct as far as led lights putting off less heat. However it depends on your type of led lights you have in order to know how close you can set your lights. I use led lights and the manufacturer says to keep the lights 18 to 24 inches away from the plants. Hope this helps. Good luck and welcome to the cannabis growing world.

no the ppm on my water is always really really low I think even with city water its almost at distilled water levels. So if the ppm does change I can't notice it. My light says 12-26 inches, but I also read that you should keep LED's a little closer because they aren't as intense as other lights.

It's a combination of nutrient burn and high ph.

Lower your ppm to 150-250ppm and get your ph down do 5.5 - 6.5.