http://boards.cannabis.com/plant-pro...hy-how-do.html
Follow the directions in here EXACTLY.
Your low pH has locked out all the metals. That's why it looks like a REALLY bad Mg deficiency.
When the soil dries out from the flush and pH adjustment, get that plant into a larger pot of an unfertilized potting mix such as promix that has plenty of lime in it, and give it tap water at pH 6.7-7.0. The soil in that pot has had all the lime used up and you are now seeing what the true pH of un-buffered peat is!