You can't have too much oxygen, (well actually, you could, don't go injecting pure O2 or anything crazy like that, too much oxygen is a poison, but you are not going to encounter that in a fishtank) but you can have too much surface disruption if you have a planted tank. Surface agitation adds O2 to the water, and releases CO2. So bubblers are great for fishtanks, but not so good for planted tanks because the plants need CO2 and surface agitation drives it off. Bubblers can also be stressful to fish that prefer water to be more still, like anabatoids. If you use a biowheel bubblers don't really do anything for your O2 since the water is well oxygenated by the bio wheel. This is why biowheels are also not the best choice for a planted tank although they are excellent for fish only tanks.