Can you post a link for the stuff your getting please? I'm planning on getting started on my MTS when it gets a little warmer, but I was unsure where to get that stuff. I would feel safer about buying the same as someone else so I know I'm getting the right stuff.
Not too get too off topic, but I've never seen why you can't use more potash if it is the one that always runs out first. I would guess that it just dissolves at the same rate so you end up with higher levels for the same short amount of time. I also am assuming there is no known slow releasing substitute you could use in larger quantities to avoid the potash dosing later.