Heavy angling pressure will help. Do you have LMB in your pond? LMB in the 12"-16" range will be the most efficient predator on the crappies. Some studies have also indicated HSB are possibly efficient predators on crappies as well. However, it would take too long for newly stocked HSB to get to a reasonable size to prey on your new BC. If you have bass, they should help. I would also target and catch and keep every BC you catch. If you start to see that they are spawning and causing issues, you can invest in a fyke net and look into using them to remove large numbers of BC that way...