I have about a 12 incher, he's in a 320 with a few oscars and a couple shovelnose. He's about 4 years old so yours has to be quite a bit older, right?
I am not sure what my bgk eats, for about 2 months now I haven't been giving that tank any bloodworms, so he has to be scavenging after dark, it's the only answer.
Yours is awesome, looks very healthy well. Enjoy!