Small poop

At night I separate my two chinchillas in their two level CN cage. I've noticed Mr. B leaves some pretty small poop in the morning, and am trying to figure out what is causing that. I removed his small pet select grass chews so that he only has timothy, orchard hay, oxbow essentials pellets, apple sticks and sometimes rosehip chips for a few days. But there were still small poops the next morning. These seem to only appear sometime late at night, because during playtime/evening he has...

Small poop