Whats wrong with my goldfish?

Ihave 2 goldfish, just your average buy in fish shop with small tank fishies... i recently put them in a huge aquarium tank with pump new gravel and couple of ornaments to keep them happy, they are really active and look very healthy and happy, thanks to new tank. but they are constantly gasping air, swimming to the top, then swimming down, blows some bubbles then back to surface to do the same.. i saw they were both pooing the other day and it had air bubbles in it.?? strange lookes like diamonds lol. I dont know if there gettin too much air or not enough. a friend suggested putting a bubble feature in the bottom get more air down below. can any one advise are they okay?