As has been said, stock coppernose or native BG instead of HBG in your main fishing pond.

In your crappie pond, I would stock it golden shiners(GSH) this spring and give them a chance to spawn before you stock the crappies. I would then stock 50 black crappies and 20 HSB in the fall. Leave the cover out of the pond... This will allow the HSB to more effectively prey on the crappies. Also, you're most likely going to have to do manual removal as well. Keeping the pond obstruction free will allow for more efficient trapping and seining of your crappies.