I've been looking at filters, and so far I like the aqua clear. Thing is, how big is the intake tube? I lost a neon tetra due to the filter that came with this tank.
To answer a previous question you had, no, carbon does not filter out ammonia, or any other nitrogenous compound. It just filters out things like medication, tanins from wood, and things like that. It also removes trace elements, which are beneficial to fish. That's why I only use carbon after medicating to remove traces of medication.
As far as the intake tube on the aquaclear is concerned, if you have small fish you need to use something called a pre-filter.
^All those intake tubes have prefilters on them. Just take a piece of foam (like aquaclear foam), cut a slit into it, then bore the slit out into a circular hole with your finger (or if the intake tube is very small, like on an Aquaclear 20), use the blunt end of a pen or pencil. Slide the foam over the intake tube and job done. Make sure to keep it clean, so the flow to your filter isn't reduced.
Aquaclears are, in my opinion, the best hang on back filters. You get a lot more capacity for actual media instead of a bunch of wasted space.
I suggest you get your hands on some good biomedia. Maybe get a liter of Eheim Ehfisubstrat pro (small, round sintered glass media) and put that in the filter on top of the foam block. Use a media bag (aquaclears come with one. They also come with very crappy biomedia. Use it if you want but it's not as good as the Eheim stuff).
BTW Tetra Safestart is very good stuff. Keep using it until your tank is cycled. You can also use Prime or Ammolock to deal with ammonia/nitrite and ammonia (respectively) spikes along the way while you're cycling.
As far as feeding your betta goes, if they are 1 to 2mm pellets, feed it 2 or 3 pellets 2 or 3 times a day, and keep an eye on his belly. If it swells at all, cut back a pellet or 2 per day. Also, bettas do well on stuff like frozen brineshrimp, daphnia, bloodworms, and chopped up mysis shrimp. Your other fish should appreciate it also.