In our best experience, using a clean flush out can help and analyze the runoff, or do a slurry to check pH of the media. A worm castings tea/reintroduction into nutrients after the watering can help, but it looms like you got potassium, calcium, and magnesium all in a bind. Do you have any amino acid dominant products? They can help chelate the nutrients and unlock/keep available. Best of luck, my friend!