How much Blue Buffalo do you feed an active dog?

Hey guys! Me again, asking about Blue. I am currently switching my dog over to the regular Blue Adult chicken, because they only had that kind in the small bags. He will be on Large Adult when he is done, though. So I was wondering how much Large adult do you guys feed your very active dogs? He was eating 4 cups of Eukanuba, and seemed to stay on weight, but since I have lowered the amount to 2 cup Euk and 1 Blue, he has been losing a little weight that he needs to keep. Now he is eating 2 cup Euk, and 1 1/2 Blue and he is gaining some of it back, I believe. When I am all done, how much should I feed him daily?