Standby Agreement. An agreement between the issuer of a security and its underwriters stating that the underwriters are responsible for any unsold portion of the issue. That is, the underwriters agree to buy the remainder of a new issue if they are unable to place its entirety with investors.
A sponge has water flow in through the pores. The water contains the food and oxygen the sponge needs. Respiration. A sponge takes in water through its pores and in more advanced forms, with canals that move the water to all throughout the sponge.
If you use an air pump to power your sponge filters, there is no need for extra air stones in the same tanks. The bubbles from the sponge filter will achieve the same purpose as the bubbles from the air stones. Some aquariums use power filters. This type of filter creates a waterfall as the water run through it.