How did you apply the copper fungicide? Be VERY careful with that stuff not to get it in the soil. Once you have a Cu toxicity situation, it's VERY difficult to fix.
Epsom salts in the soil are another bad situation.
You will want to flush WELL with tap water set to a pH of 6.8-7.0 to counteract the effects of both the excess metals you have added, and the acid-loving-plant food, which has too low a pH for cannabis.
Powdery Mildew on pot plants is best prevented with a horticultural oil such as Neem or SMC leaf wash. I prefer to use SMC lately since it smells a lot better, lol. You can also treat with Bacillus subtilis (Serenade from home deopt or walmart), whcih is a beneficial microorganism and impossible to overdose on, lol!

Other than that, Rusty covered it all.