As far as a filter goes I really don't know. My best answer is small. If it is rated for a 5 gallon tank it should be just fine. You don't really need carbon in your filter. The main purpose of carbon is to remove medications, odors and possible cloudyness. You shouldn't have any odors or cloudyness if you change 25% of the water with a conditioner weekly. You want a sponge filter to help trap leftover food and waste. You don't need to replace this unless it starts falling apart. If it looks dirty swish it in old tank water to remove debris. Ceramic media is a fantastic addition to a filter! It gives the good bacteria a home and never needs replacing unless it is crumbling apart which takes forever! The ceramic media will help your tank establish the nitrogen cycle which is extremely important in keeping a healthy fish. I don't think one thermometer is really better then the other. I stick with the old fashioned ones because they work and no longer contain mercury. If you are worried about your fish being sucked up by the filter you can wrap the intake with a clean cutting of nylons and attach it with fishing line or nylon thread. Hope this helps and feel free to ask more questions

 

Welcome to the forum!

The only filter I will use with bettas anymore is a sponge filter. They use bubbles to push water upward through a sponge, and the good bacteria grow on the sponge. They create the lightest current of any filter. I can't recommend any power filters for that size tank as I've never used any.

If you stay with the power filter, I would forgo the carbon. Cycles are more difficult to keep in a smaller tank, and since carbon needs to be changed every week in order to remain effective, you would be removing a good chunk of your biological filter on a weekly basis. Cram that sucker full of bio-media like ceramics. The more surface area your filter has, the more stable your cycle will be.

In order to prevent your betta from being sucked up in the power filter, some people will wrap an aquarium sponge around the intake. It has the added benefit of being more surface area for the good bacteria as well as preventing your betta from getting caught.

If by old-fashioned thermometers you mean glass, then I would go for the glass over a digital one. Good digital thermometers are more expensive than the glass ones. And yes; they work just fine. I have them in all of my tanks ranging from 1 gal up to 55 gallons.

 

I have a 5 gallon right now. I am using a "normal" filter. It's made for small tanks. It's completely adjustable. The only con I've found in my years of using it is that it's a pain in the butt to clean because its small, but it works wonders.

The flow is completely adjustable since bettas don't like strong currents. The filter pads are cheap too! You can even make your own. Here's the filter I'm talking about: http://www.amazon.com/AZOO-AZ13097-...EWCMO/ref=wl_it_dp_o_pC_nS_nC?ie=UTF8&colid=1CU1TOZQ11M4H&coliid=I1L3EYONFP1R1I


I worried about my Betta's tail getting sucked up in the filter. So I got one of these and put it on the intake (where the water gets sucked up) and secured it with a rubber band. http://www.petsmart.com/product/index.jsp?productId=3650250

 

i personally love the aquaclear filters, i have two 5 gallon tanks both with aquarclear 20 filters on them but i have set the flow to the lowest flow. my bettas dont mind this at all. actually the flow is really really low when its set all the way down, i occasionally move it to high to get rid of protein film and my bettas dont even mind it on high but i never leave it on that anyways. plus they come with foam, carbon and biomax so u have all 3 media that can be switched out whenever, if you dont want the carbon you can take it out and add something else in its place