I have a 55 gallon tank with two large goldfish and three snails. I use an Eheim Pro II 2028 canister filter. The water coming back into the tank from the filter seems to put out a lot of bubbles. Is this oxygen? Is it enough oxygen to keep the fish healthly?

is the water breaking the surface? that seems to be the operative word on O2 exchange. a ripple will due. just something to break the tension and i'm not talking cocktails here.

could be surface agitation or air inside your filter being pushed out

As the water is released from the spray bar, you set it so it sprays just across the surface of the tank. This exposes the greatest amount of water surface to the air. Oxygen is picked up at this time. The more water that is agitated and comes in contact with the air, the more oxygen is picked up.

A bubble bar or such will help lift water from the bottom corners of the tank to the suface, exposing them to the oxygen and increasing your tanks levels.

Unless your tank is running very warm or is overstocked or being medicated, chances are that the agitation from a well placed spray bar provided ample oxygenation.