Yo Ho Ho guys! mery xmas!

starting my hydro grow in the next couple of weeks, going to be using a bubbler similar to stealthhydro.com's 6 pod system....anyways..

im confused over the subject of pumps.

So there are Air Compressors and Submergables, and these have tubes connected to airstones or airtubing.

whats the different characterists of the 2 and why do most peops use compressors?

Also (and most important) how powerful would the pump need to be for a 50ltr / 13gallon reservoir, growing 4 plants in?

cheers!