Newbie needs help please!

[TessaRuth]

We rehomed a Horsefield tortoise from a friend last week. He doesn't seem to be eating much. His previous owner fed him on tortoise pellets which we have also given him, along with lots of greens/weeds, but he only seems to eat about ten pellets a day. Is this enough? What weight of pellets should they eat? He is very active and spends about an hour a day walking around our terrace and looks healthy. I weighed him when he arrived and then yesterday when I found he'd lost 5g. This worried me as I have no idea what he should weigh so I the Donohue method which I believe is suitable for Horsefields, I measured his carapace length in cm at 14.5, then cubed it and multiplied by 0.191. This gave a target weight of 582g but he weighs 815g. Have I used the wrong method or is he just overweight? I don't know what a fat tortoise looks like. But my main worry is whether he is eating enough. Very appreciative for any help.