You may want to consider putting more cover in the pond where the CNBG could utilize it during lower water levels.

I would definitely consider stocking more CNBG of an advanced size as well. You can look into stocking another batch of GSH as well to help supplement the population you already have in there. Tilapia are also an option as an annual stocking. They may help take the pressure off your CNBG.

HSB will eat anything they can get in their mouths, but will really like the GSH. Gambusia or mosquitofish are also another option to stock. They are small in size but are about impossible to be completely predated out of a pond.