Is he active? If you just fed recently he likely won't be. If it's been more than six hours he should be moving around a bit. Is your return from the canister fully submerged, or slightly out of the water to break the surface? That creates a gas exchange that should be sufficient but it can be noisy. Adjust the return or add some air and just keep an eye on him. Is there anything else in the tank with him? I only ask because when an RTC passes they skunk the tank almost immediately.