Start dosing

Just kidding....
Increase your flow and change your pH to 6.7 perhaps? That would increase the output and reduce build up and raising the pH would dissolve less. I don't know if this is whats going on or not, but it sound like your dissolving more than you can get out, so you reduce the amount you dissolve, increase the flow and see if that changes your effluent dkh at all. If you get a lower number, the increased flow will help off-set that.
The thing I am going for here is a lower concentrated effluent, but more of it. It sounds like its too concentrated and not enough right now.. make sense or am I blowing smoke out my backside?
What kind of pump do you have on it? And what kind of media?