you need to get a heater and a filter, and feed him thawed frozen blood worms instead of a quality pellet like new life spectum betta pellets, 1-2 times a week.
A 5 gallon tank is the samllest tank that can hold a tempurature stable, which is wat this tropical fish requires to live a happy healthy life. Yes many bettas servive a long time in unheated bowls, but they suffer the entire time.
So yes, this is better then a cup, but not that much better. please upgrade ASAP!
Rice paddies, were a lot of wild bettas originated from, expand for miles, are about 3 feet deep, are full of nutriant rich plants.
Killi fish and some loaches, have managed to somtimes servive in puddles, or hid eggs in the drying up mudd to preserve the species when the next rainy season comes. One species of loach was found hibrinating in trees above a dried up water source.
But that is survival emergency tactics, not happy fun time.
1 Betta needs a 5 gallon tank. With an adjustable heater of 5-10 watts per gallon, To keep the water at a stable tempurature between 78 and 82. All fish need a filter to create a cycled environment free of toxic ammonia. Anything smaller then 5 gallons is nearly impossible to heat stabally and keep cycled.
It is best to cycle the tank before adding fish.
http://www.fishlore.com/NitrogenCycle.ht...
It would be a good idea to buy liquid testers for ammonia, nitrite, nitrate, you can skip ph if it is just a betta, they can adapt to a very wide Ph range, but be sure to still float then acclimate the betta to the tank water
http://www.fishlore.com/acclimating-trop...
Use a gravel vacuum to change 20-35% of the water once a week while sifting gently through the gravel. Replace with treated tap water that has a very similar temperature as the tank water. A stresscoat product that also dechlorinates is much better than just dechlorinator. It helps fish grow healthy immune system "slimecoat, it can be added if the fish has a torn fin, or is ever netted or handled for any reason. API stresscoat with aloe is a good one. Prime is too diluted for a 5 gallon tank, one capful treats 50 gallons.
Feed a variety of foods including a healthy pellet and or flake and frozen thawed worms,shrimp,daphnia 1-2 times a week. 3-4 pellets or the equal amount in other food once a day, or split to twice a day.
A betta hammock or live or silk plant will give the fish places to hide and rest. some bettas can be trained to hand feed, or do trick, or play with a ping pong ball, their are videos on you tube.
In a 5 gallon a snail, maybe shrimp are the only option for tank mates. In a bigger tanks their are other fish that can live with a betta.