Small fish bowls from 2.5-gallon to 10-gallon fish tanks can be a real challenge to heat properly especially when you are worried about where in the small tank the heater will go. By the time you set up your decorations, gravel, plants, and rocks, there is not a lot of room for much else—especially not a heater. Fortunately, there are mini heaters available in a variety of types.
Tropical fish like betta need warm water to survive. Rapidly rising and falling temperatures can cause your fish stress, which can soon lead to death. For this reason, a heater is essential for a small tank, no matter how cramped it may be. Temperatures change much more quickly in a small tank than in a large one.
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Available in 7.5 and 15-watt sizes, this flat, fully submersible heater is a great choice for a small tank. It fits flat against the side of the tank, or better yet, under the gravel bed. The price is also fairly low and the smaller version is perfect for a betta tank or bowl. In order to keep this heater small, it has been stripped of virtually every feature. It is little more than a heating element and a cover. These heaters are "plug and play," and are always on. The only safeguard you have with this heater if you choose the correct size for your tank.
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Zoo Med specializes in reptile needs, which require a variety of heater products. The company brings that expertise to the Betta Therm heater, which is a flat round heater, designed specifically for the bottom of a betta bowl. It has an auto-shut-off feature once the water temperature reaches 78 F.
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A relative newcomer, this pre-set heater has been well received by owners. This 15-watt heater is preprogrammed with an automatic shutoff at about 78 F (26 C). It is slim and compact making it easy to conceal behind ornaments and decorations. It is ideal for desktop systems. It is safe for freshwater and saltwater tanks up to 5 gallons in size.
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Available in 5-, 10-, and 20-watt versions, the Cobalt is fully submersible and shatterproof. Like some other mini heaters, there are no adjustments. It is always on. This is one of the more durable heaters for its category.