I know I said I'm not a hydro guy , but I couldn't help but notice that your pH is pretty high for a hydro grow. I'm assuming your testing the pH of your nutrient solution and is where the 6.5 came from, but I think optimal pH for most hydro methods is 5.2. You should wait until someone with more experience in hydro can chime in, but it's something you might want to think about.

Also, if you're using distilled/RO water, you should also be using a product called CalMag Plus to replace the Mg, Fe, and Ca that has been filtered out. This might have something to do with those rusty blotches you're seeing.