The Aqueon LED 20 Aquarium Kit comes with everything you need to start a new fish tank, including a heater and thermometer. ... "It is harder to keep a small fish tank than a big fish tank," said ...

Step 3 – Add a Heater. Bettas are tropical fish that prefer water temperatures between 76–82°F. A small, adjustable aquarium heater is essential to keep the water warm and consistent.