Eclipse systems are an option. All-Glass kits are better (filter they come with are superior to the bio-wheels).

Here is a link that might be useful: All-Glass kits

I would say a 2.5 gallon tank will a light flow filter and either live plants or fake plants (silk) and gravel. Try Mini-Bow aquariums.

As above and here is site mentioning great information re betta care. Remember some offices shut down temperatures at night on weekend so large enough for heater. What to do if heater goes crazy and you are not there??? I noticed on my Eclipse, the engine for the filter system heats up, and until my heat didn't come on in apartment I could keep heat up to 80. You will have to check that as temp flucuations are a number one cause of disease in bettas. I also add sponge around uptake and break one apart and put in outlet (just slice a pice and have each end going out of outlet of filter - obviously bio wheel is removed, but sponge will take place of this bio activity) Or in regular tank, canister box filter (not sure exact name but old fashioned type) you can buy valves where you splice air tubing, to reduce air flow to make it gentle for them. They love plants, come from planted spaces in wild (for the most part, some live in colder streams) (no not mud puddles a few inches big, lol) Butterflys of Asia, as they often sit on leaves, and sleep on them at night.

I place live plants under water outlet as well to reduce flow. Little glass cave (black glass coffee cup) - all is well. I change water twice a week, about 10-15 % (not sure in 2.5 gallon about 1 - 2 inches) Feed once a day, meat meal, and light spiruline/algae flake later meal. Their stomachs are as small as their eye, so don't let them fool you with their puppy dog wiggle for more food. Remember they jump especially when placed in small space. leave a bit of air at top so they can come up to breathe. Best Sherry

(remember the larger amount of water, the more stable the system is, 2.5 - 3 gallons at least, mho)

http://www.bettatalk.com/

The best tank for your betta will be one that falls into your price requirements and space requirements. For example, because I have many of the materials I need already, a 10 gallon was the best tank for my betta. I already had the filters, the heaters, enough gravel, live plants, and bacteria for the cycle. Transferring to a 10 gallon was easy and I had the space. However, before I didn't have space for a 10, so a 5 gallon worked out for me.

If your betta will be living on your desk, a 2.5 gallon is feasible. Your betta will need a heater for the winter months, as well as a thermometer. Gravel is unnecessary because you will likely not cycle the tank. A turkey baster, rinsed but not washed with soap, is recommended to suck bits of poo and gunk off the bottom of the tank between water changes.

With a 2.5 gallon tank you will need to completely empty out and scrub down (again, no soap) the tank every two weeks. On the off weeks, a 50% water change is recommended (you'll need an empty gallon jug and a siphon for this). Bettas should be fed 1-2 times daily, 3-4 pellets per feeding or less depending on their size, and they should be kept at 78-80 degrees Farenheit. Avoid plastic plants and go for the silk ones.

We have been keeping our pet Betta in an Eclipse 3, with lots of live plants and some red ram snails for 4 years now.

I don't use a heater because our house is climate controlled but I also believe live plants are highly beneficial to good health in any FW tank set-up.

Small as it is, the E-3 supports 3 moss balls, a small anubis, a carpet of dwarf sag, and a clump of java moss.

Sammy The Betta loves to swim through the plants and sleeps nestled into the java moss, which has attached itself to enough of the gravel that it stays in place.

He eats any newly hatched snails, so keeps their numbers in check, while the adult rams keep the tank free of algae.

I do a 50% water change weekly and as I've learned how to clean and refill the cartridges, I pop in a fresh one every other week, removing the entite filter unit for a complete cleaning every other month.

So far: so good. Healthy tank: healthy fish, and a lovely display.

Also: the light is plugged into a timer. I like the separate light cord on the Eclipse for that reason.