Well you're gonna wanna look at the packaging. It should say up to 5 gallons, up to 15 gallons, or up to 30 gallons.
You'll want one that's up to 5. =]
What you're talking about sound like an under-gravel filter. :/ Those aren't all that great. in fact they're pretty much useless and can often cause more trouble than they're worth.
If you'd like a better filter I suggest getting a
Tetra Whisper 3i filter! =]
A filter in anything less than 2 gallons is pretty much a waste of time because you can't cycle it anyway. So I wouldn't waste the money on a new air pump (if yours is broken) or a new filter. I'd just take out the under-gravel one and the gravel in your tank. Then I'd just keep the tank bare bottom and do the required every-other-day 100% changes that are required for 1 gallon tanks. =]
If you actually have something bigger than a 1 gallon (say a 2 gallon or up) then you can go ahead and pick up the tetra whisper filter, a new air pump (if yours is broken) some airline, a "T" valve (or something like it that lets you adjust airflow), and you'll be set to go! =]
If you need a picture of how to set up your air pump and tubing ect I've got one I can show you! =]
Check out the eBook Betta Fish Care Made Easy
