A check valve is an important accessory if your air pump is below the water level of your tank. When the air pump shuts off, water can potentially flow back up the airline and into your pump, ruining it. This inexpensive part prevents that from happening.
Airstones are approximately 0.75in square (on the bottom) and about 1 inch tall (not including the stem). They are made of sand and come in one, two, and four packs.
Rivers to Reef says: Hoping for those long sand stone airstones? We usually don't recommend them. Why? In order to make full use of an long airstone you would need an oversized pump to reach the end. We recommend bubble wands instead (Click here).
Bubble wands don't have the same power requirements that sand stones do. Truthfully, don't buy a wand for more aeration, just get it for looks. A simple one inch air stone or two will provide the same amount of oxygen to your fish, not to mention they are much cheaper.