We LOVE Acana grain-free!!!
Bandit and Nala have hard small poop too...not to be too graphic, but it looks kind of like "deer pellets" it's not like a log anymore. They haven't had any upset stomachs and were on about the 20th pound of food and for Bandit that's a miracle

If he's constipated try adding canned 100% pumpkin. That may help.