Oh? I've never seen my cories eat BGA whenever I get a break out. I just pipe a little H2O2 at the area and leave the filters off for 10 minutes or so.Just add some cories. They eat that kind ò algae super fast
In the past when I had a wide spread bloom I used tank wide dosing of H2O2 and Excel to kill BGA. Ensuring you don't bottom out on nitrates will also minimize BGA blooms.