Bill welcome and glad to have you here. Theo and Dave answered your question. Add some adult CNBG as you planned and then a few more next year, over time that will work. You may need to reduce the # of small GSF/HBG by either the LMB eating them or trap or seine as they will eat way to many of your CNBG offspring.

You will learn the art of it as well if you keep at it for a couple years. Experience is a great teacher and there is a lot of it here.