[judya]

Also I wouldn't recommend puffers in that size tank. As I understand it, they are very aggressive, and also maybe more delicate than some other fish. Cute, but not an easy fish.

Cycling is an ongoing process. A betta, or any other fish, will help to cycle a tank, but it will be cycled with only enough bacteria to handle that one fish's waste products. As you add more fish, the numbers of bacteria will need to grow as well, and will, because the fish are providing them more food, but it takes time for the bacteria to grow and reproduce enough new bacteria to handle the new total waste.

Fishless cycling gives you a jumpstart in providing ammonia to feed a large quantity of bacteria, so more fish can be added once the bacteria colony is going, but still takes some time. There are also products that are supposed to add bacteria, such as Cycle and other products, but there's mixed opinion on how well they work.

Using hardy, hard-to-kill fish for cycling is only because they are less likely to die in the process. Some fish are very sensitive to ammonia and nitrite, and should wait til the tank's well established.