I'm essentially struggling with the same issue. I've drastically lowered ppm to 300 and I think it's doing better (it's been 2 days). I couldn't tell you what was going on with my plant, I think Mg was being locked out due to excessive potassium.
In any case. I'm not pro, but according to my readings, soil fertilizers should not be used for hydroponics. Hydroponics fertilizers come in chelated form which can be used directly by the plant, whereas soil fertilizers first have to either decompose or react with the CO2 being released by the roots. Using soil fertilizers in a hydroponic context might work for a bit but will eventually lead to toxicities as well as deficiencies. (Miracle gro is for soils right?)
What I would do if I were you (and I strongly suggest you get a second opinion on that) is to heavily flush your medium with a balanced 100ppm hydroponic nutrient solution and resume from there, slowly increasing concentration as the plant gets better. That's essentially what I've done and I think it's working (I'll update you on that in the next few days).
To be honest, it's really hard to actually get good advice (or advice at all) on forums, seems people are more talk than anything else. Whatever bro, our boon is that of experience, and soon, you and I shall be smoking the good stuff.