Occasionally my goldfish will gulp at the surfsce of the water. Usually about 10 minutes after I feed he goes to the top and gulps for 1 - 2 minutes. I don't understand why he would be doing this because I pre-soak the pellets before I feed and they sink straight to the bottom. I highly doubt that it's from a lack of oxygen because I use a good quality air pump and I aim the canister outtake slightly up so it creates a lot of agitation. My other Oranda doesn't exhibit this behavior. I don't want my fish to develop swim bladder issues, so what can I do to prevent him from doing this?