Looks similar to nute burn to me. The ph sounds okay for soil. A little high if in hydro but still just about in the safe zone. keep using small amounts of the epsom salts and maybe use a weaker nute for a while. Dont do to much at once though coz it makes it hard to find the original problem!. OH YEAH Greetings from a newbie to the board

Damn shame about overgrow.
peace