What kind of pump are you referring to Deon? Air pump? Powerhead for water circulation? Return pump from a sump?
If you meant powerhead for inside the tank (which I assume you are), I typically recommend the maxijet brand powerheads as they are smaller, powerful, and last a very long time.
In a 20 gallon tank, I would aim to have 200-500 gallons per hour turning over inside the tank.
(BTW- I'm moving this post to the new reefers section for you.)
