Yeah, probably are bg, when you said they were feeding , I had a bad feeling. My experience, RES under 3" and you'll get a lot of BG and GSF . Sorry, I'm fighting an uphill battle into hurricane winds trying to remove BG and GSF . Should be #1 rule to buying sunfish species, 3" at least or don't buy. Experts can thump me if I'm way wrong. Absolutes have exceptions, nearly always, may be species that defy the 3" rule, in Sunfish or situations that do. Mine is a SMB and YP pond also. wanted RES for the multitudes of snails. Contamination of different species mixed in with other species , and not just SF , seems to be an issue at a lot of fish sellers .
