To "bleed" off excess air just means to let it out into the air rather than the tank. You will need either a "gang valve" (
http://www.drsfostersmith.com/produc...fm?pcatid=3700) or a T (tee) and a shut off valve (they come in kit
http://www.drsfostersmith.com/produc...fm?pcatid=3690).
If your pump is too big, you will waste some electricity, but you can also use it for additional air-driven filters and ornaments.