Originally Posted by Ajones108
The good news is that bettas are surface breathers, so they don't need oxygenated water. :) But if you have plants, a filter is recommended, and if you filter your tank you can start a beneficial bacterial cycle which can, in the long run, reduce the amount of water changes you need to do. See signature :)
Betta live in naturally planted oxygenated water in the wild. More than half the bacteria and fungus that will attack your pet are killed by a little oxygenation in the water. Another large portion can be suppressed with a little salt.
Several options, the best one is the Aquaclear 20. It can be turned way way down and support a full cycle of the tank. I've never met an unhappy owner.
The tetra Whisper 3i internal is great if you put a sponge over the intake or you can use an airstone sponge filter for a five gallon tank.
All three of these do a fine job at fine particulate filtering and support the bacterial biological filtration that will keep you from having to change up to fifteen gallons of water per week.
If you can, give your Betta a plant of one form or another. I've never had one, boy or girl, who didn't like plants. Several have even panicked because their plant lost leaves. Just remember that you're looking for low water output rates barely sufficient to stir the tank and to keep the bottom media thickness under 3/4 of an inch without plants and never over two inches until you're very experienced.