What are you trying to achieve? Eliminate the GSF and create a BG only forage pond? If your goals are a 100% pure BG forage pond I would drain, seine and save any BG, and nuke remaining water with hydrated lime, refill, and restock with remaining BG buy more if necessary. If this is a forage pond, not sure why presence of GSF are a concern, as predator fish aren't picky regarding lepomis species as forage.
Clarify your goals and will share some thoughts.