Yeah nothing to worry about. I had a LOT of grown up GSF when I bought my pond. Just LMB, and GSF when I bought it. I had some GSF that were 10 inches long. They are fun to fight mind you at that size! I got rid of some of them but ever since I put in my BG, CNBG and RES 2 years later I hardly ever catch a GSF anymore. I have a few very nice hybrids though so I know there are still a few in there but have not had any issues. You should be just fine!
RC