A harsh metallic taste and super quick burn? Like overdry weed just fries right up? Then you haven't gotten your nutes out.

I use Pro Blend and as long as I flush no problems. But hydroton is notorious for "hanging on" to excess salts and ferts with all it's cute litte airy holes and can cause overfert/salt build up issues. It's one of the reasons I don't use hydroton.

I say change your medium, use a good flushing product and RO water (and Cannazym) for at least a week to flush and you should be good.