Sorry, I don't know of anyone in your area to test pond water chemistry/nutrients. But, I did a quick search and found this dept at the UNL (
http://waterscience.unl.edu/ ). They may be able to offer some suggestions or testing labs.
As for the LMB stocking-sizes: if they can fit in a catfish's mouth, they will be eaten. Even if they won't fit, a cat may still try to eat 'em. I've found dead catfish with forage fish lodged in their mouths. Their confidence sometimes overloads their throat.
In my opinion, the 3-4" LMB were too small to stock in a pond that had 1 - 1.5 lb. cats.
