The Tetra 3i is a sponge filter (uses air-bubbles to circulate the water). Unfortunately, is very poorly designed. The water flows only over the top 1/4 of the filter cartridge; it should flow through
the entire cartridge.
Many Betta keepers recommend sponge filters. You can learn more than you'll need to know on this thread. http://www.tropicalfishkeeping.com/b...hy-how-126530/
There are several sponge filter threads active right now. You can direct questions on any of them.
Sponge filters are particularly useful in small tanks (<5gal) because the large sponge can house lots of nitrifying bacteria which eats the ammonia in the tank.