protein skimmer for 30 gallon

eveyrone is telling me i need one with the amount of fish i have. i was wondering what size i should get. i dont want something that take sup a lot of room in the tank. is a 20 gallon one okay even tho my tank is 30 gallon. help me out im a dummy with this stuff

also found some cheap oens on ebay are they ok or just plain crap

Nano Air Wood Protein Skimmer - eBay (item 370401433345 end time Jul-03-10 01:00:21 PDT)

Oceanic Bio Cube Protein Skimmer Size 14 & 29 New - eBay (item 350371048563 end time Jul-30-10 17:16:44 PDT)

AquaticLife Internal Mini Protein Skimmer 115 - eBay (item 180526934199 end time Jul-04-10 09:42:03 PDT)

 

How much are you willing to spend? Here is a really good protein skimmer that has a very small footprint, I use it in a 29 Biocube:

CPR SR3 Sump Protein Skimmer - Fits in BioCube 29: Premium Aquatics

Here is a hang on the back that I have used that works very well and can even run a little carbon (and it is very inexpensive):

Taam Rio Nano Protein Skimmer

 

that taam rio looks good for the money. even though it says its good for 20 gallon can i still use it for my 30 gallon. i figure with the 30 pounds of rock and 30 pounds of sand there is about 20 gallons of water

 

do i need to buy a pump for the taam rio?

 

I think you would be ok, it is a little undersized so you will have to empty often. It comes with a pump that draws water into the skimmer. Works similiar to a HOB filter. I think it will work for your application.