And,
''The general philosophy behind the air system is to complete an air path of equal pressure throughout the system. The easiest way to do this is to design the system on one main loop. The pump forces air into the loop where it travels around the loop to each of the drops to individual tanks. Any air that isn't expelled into a drop remains in the system. This creates a closed loop. All exits from the loop will have the same air pressure. In addition, the pump will have to work less because there is a constant pressure in the system. Pumps, like people, will last longer when they don't have to work hard.
The main loop was constructed using 1 inch diameter (inside measurement) reinforced vinyl tubing. The tubing is buried entirely in the ceiling between shelves and penetrates the ceiling to drop down at the leading edge of the top of each shelf unit. The drop runs the length of the top shelf at the front and then penetrates the ceiling agin. The drops to each aquarium were created by drilling holes in the main loop at the appropriate places along the shelves. A brass valve is screwed into the drill hole and acts as the control for the airline which is pressed onto the valve. The drops may be split as necessary to supply the various tanks below. It is best to drop a separate line to each tank from the main loop, because adjusting one line will not change the pressure in another.''