How long have you have the Gig? They do eat very well when healthy. Over the last 6 months or so mine (16-18 inches) wipe out most of the fish in my 93 g Cube. The survival included the clowns, one Leopard Wrasse and a Red Sea Sailfin tang. The expensive meals included a Mandarin, a 4 inch Purple tang, 5 Royal Gramma, (yep the whole dumb harem), three Yasahasi gobies and a large Marine Betta. All of these fish, other than the Marine Betta, was in the tank before the anemone and all doing very well prior to death's arrival. I though the Marine Betta would hang around inside the rock structure instead of venture close to the anemone. It took him only 36 hrs or so to spit out the white, flesh devoid-ed, bones of the Marine Betta and the Purple tang. All these time I have night light on the tank, and have a rather aggressive pair of Onyx Percula in the anemone.
My anemone seem to reach max size and have spawned regularly about 10 days or two weeks after each large meals (the purple tang) or if I feed him twice a week with about 3 cubic cm of shrimp. I have since stop feeding him other than the fish food and occasionally a small piece of shrimp or fish (1 cubic cm). When I first got him into the tank and he start to do well I feed him 5-6 cubic cm of shrimp or fish every 2-3 days.
From the look of your anemone and fish, I estimate your anemone to be about 6 inches in diameter. I would feed him 2 cubic cm every 2 to 3 days to get him to grow. If you don't want him to grow, 1-2 cubic worth of food every week or 10 days. As long as he doesn't regurgitate, he would be fine with this amount of feeding. They are fish eaters and when healthy can handle large amount of food without problem.
Good luck with your anemone. They are beautiful and deadly in our tank.