now i've been reading that in some cases air pumps are for decoration......im letting you guys take that one......is it absolutely positively neccessary to have an air pump.....if so why?i am being serious so please dont laugh at me.
While not strictly needed they do a lot of good in a tank. They break up the surface tension which results in better CO2 and oxygen exchange between water and air. So even when they are put in only for decoration they are doing great things as well.
They're usually not needed if you have any type of filter thats disturbing the surface. I find them loud and the bubbles quite annoying, and so i never use one normally. They are good to have as backup in case a filter fails, and some people enjoy the bubbles.
Water movement at the surface contributes to oxygen dissolving in the water. Gas exchange occurs at the surface of the aquarium. Bubbles from an air pump do nothing but disturb the surface of the water to promote this gas exchange.
good luck