Try doing the quart jar test. Mix your products together in a quart jar, shake em up and see if you get a precipitate. If the chemicals react, it will usually happen quickly. If you get sludge at the bottom after a while, it may be that you are trying to suspend too much material in the solution. If this is the case, try using less fert, and see if the problem goes away. Adjust your walking speed accordingly, and you should still put down the same amount of fert.
Agitation can be as easy as running a secondary pump (12v will probably do). Plumb a line out of the bottom of the tank to the pump, and then back in the top of the tank. You may have to be careful about foaming if you do this, but antifoaming agents are available.
Hope this helps.