Best Rated Small Aquarium Heaters for Nano Tanks

One of the key components of a successful aquarium is a stable water temperature. When the water temperature is below the recommended level, fish and plant metabolism slows down. Sudden drops in temperature are especially stressful to fish. Low temperature inhibits the fish’s immune system and may lead to disease problems.

Most tropical fish like tetras, rasboras, cichlids and even bettas need warmer water parameters, and therefore will require a heater. 


Siamese fighting fish also called Betta splendens swimming in a big planted aquarium


Cobalt Neo-Therm: Most customizable & reliable.

PLACO 25W: Most economic & beast for nano Betta tanks. 
My Top Pick:


Best Heaters for Nano Aquariums

1. PULACO 25W Small Aquarium Betta Heater

PULACO 25W Small Aquarium Betta Heater

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This tiny heater works for marine and freshwater nano aquariums, betta tanks, for example.

The design is based on the traditional glass tube with a wound metal heating element. Think of it like a traditional glass heater, only much smaller.

There is no temperature adjustment knob. Instead, the Pulaco uses a pre-set temperature rated to keep tanks up to 6 gallons at 78°F.

The heater has an LED light that is green when the heater is powered up and red when heating the water.

The heater attaches to the side of the tank with a suction cup and must be positioned vertically in the tank.

The power cord is four feet long. The heater measures five inches long.

2. NICREW Mini Aquarium Betta Heater

NICREW Mini Aquarium Betta Heater

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The Nicrew heater steps away from the traditional glass tube design.

The heating element is encased in a plastic polymer body. This makes the heater unbreakable.

The temperature is pre-set to 77°F (25°C), making it suitable for freshwater tropical and marine tanks. The heater is available in 15 to 75 watt models. The 15-watt model is rated for 2.5-gallon (10 l) tanks. The heater measures only 3.3 inches (84 mm) long.

It can be mounted inside the tank in any position using the two suction cups. The heater must be fully submerged.

The green LED indicates the heater is powered up. The red LED indicates it is heating the water.

3. Aqueon Submersible Mini Flat Heater

Aqueon Submersible Mini Flat Heater

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This submersible aquarium heater is very thin, measuring only 0.5 inches (13 mm) thick. The heating element is encased in a shatter-proof polymer.

Three models are available for tanks up to six gallons (20 l).

The Aqueon heater can be mounted vertically or horizontally. The 7.5-watt heater is rated for tanks up to three gallons (10 l).

The heater raises the water temperature about six degrees above room temperature. The thermostat cannot be adjusted.

The Aqueon Flat heater does not have LEDs to indicate when it is powered up or heating the water.

The heater is available in 5-, 7.5- and 15-watt models, for aquariums up to ten gallons (40 l).

4. Fluval P Series Submersible Aquarium Heater

Fluval P Series Submersible Aquarium Heater

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Fluval is one of the major aquarium equipment brands in the hobby.

The P- series heaters are encased in a shatter-proof polymer. Accidental falling rocks and big fish, like cichlids, won’t be able to break it.

The P-series come in three models:

  • P10 has 10 watts rated for tanks up to 3 gallons (10 l)
  • P25 has 25 watts rated for tanks up to 6 gallons (20 l)
  • P50 has 50 watts for tanks up to 15 gallons (50 l).

The heater features a LED running light that glows red when powered on. The heater will keep the water temperature at 76-78°F (24-25.5°C).

If your room temperature is 12-degrees below this range, the manufacturer recommends using the next higher output heater.

The P series heaters can be used in freshwater and marine aquariums.

The heater attaches to the glass with a suction cup and can be placed in any position, if the heater is fully submerged.

5. Cobalt Aquatics Neo-Therm Pro Aquarium Heater

Cobalt Aquatics Neo-Therm Pro

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The Neo-Therm Pro aquarium heater is the most advanced in our line-up.

The heater design uses a flat polymer body and a large dial packed with LEDs that indicate the temperature setting, water temperature, and status of the heater.

While traditional heaters are either on or off, the Neo-Therm ramps power up or down to make gentle temperature adjustments. This saves energy and keeps the water temperature more stable.

Temperature can be adjusted from 86-94°F (30-34°C).

The advanced electronics automatically monitor for overheating and shuts down the heater if there is a problem.

The slim design uses a reversible suction cup mount system, making it easy to install in the aquarium or a filter.

The Neo-Therm Pro also works with automated reef control systems. The heater is available in six power ranges for aquariums up to 55 gallons. The 25-watt model is rated for aquariums up to 6 gallons.

Final Thoughts

Apart from physical size, it is important to consider wattage when selecting heaters with pre-set temperatures.

If your room temperature runs about 10 degrees less than the pre-set temperature, the heater may not be able to maintain a stable temperature.

You’ll probably need a heater with slightly more watts. Choose the next higher wattage model.

The PAULACO, Aqueon, and Nicrew heaters are best suited for small betta tanks in rooms with temperatures around 70F.

For nano aquariums of larger size, the Fluval P series offers a variety of wattages. For full control of the temperature setting along with advanced LED display and temperature control, the Neo-Therm heater is the way to go.

Low Temperature and Tropical Fish

When tropical fish aquariums are too cool, several things happen.

First, the fish’s metabolism slows down. Because fish are cold-blooded, temperate plays a key role in their energy for growth and repair of damaged fins and skin.

Even worse, the fish’s immune system is inhibited. This means the fish won’t be able to fight off stress and disease problems.

When the fish’s immune system is weakened, it becomes susceptible to bacteria, fungus, and parasite problems.

Why Does a Nano Aquarium Need a Heater?

Low-light aquarium with thriving plants

Aquarists with small tanks tend to forget their aquarium needs a heater.

Even though the nano tanks are smaller and limited for space, the water temperature still needs to be stabilized.

Water holds heat and is slow to lose heat and cool down. The larger the aquarium, the more stable the temperature.

Smaller nano tanks can easily be chilled by HVAC air conditioning drafts.

Some people like to keep their home or office cooler than what the fish need. A heater will prevent temperature dips and keep the water temperature in the optimal range.

Nano aquariums don’t have room for large traditional aquarium heaters. In fact, you don’t need a big heater in a small aquarium.

Fortunately, there are a variety of small aquarium heaters designed especially for nano tanks.

We’ve looked at the most modern designs in nano aquarium heaters and evaluated the features of each brand. Our guide will help you select the right heater for your nano aquarium.