| Marina Betta | Terta HT | Hydor Slim | Cobalt Mini | Eheim Jager | Aqueon Pro | |
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| Tank Size | .5 – 1.5 Gal | 2 – 10 Gal | 1 – 10 Gal | 1 – 2 Gal | 3+ Gal | 7+ Gal |
| dimensions | 1.75″ x 2.75″ | 5.5″ | 6.5″ x 3.2″ | 4″ | 9″ | 9″ |
| Temp Display | F/C | F/C | F | F | F/C | C |
| Longevity | 1 – 2 Years | 1 – 3 Years | 1 – 4 Years | 2+ Years | 3+ Years | 7+ Years |
| Warranty | 30 Day | 2 Year | 30 Day | 3 Year | 3 Year | Lifetime |
| Price | Medium | Medium/High | Medium | Medium/Low | Medium | Low |
Compact Quality in Heaters
While many larger tanks can take on whatever brand or heater is the most trusted or you are most familiar with, small aquariums just don’t have that freedom. Instead we need to pick from the best, most compact heaters that are reliable and effective. This means sometimes foregoing the use of automatic shut off heaters or temperature controls. To do this we need extensive knowledge about the heaters we will be using, ensuring that our fish will not be harmed.
#1 Marina Betta
The Marina Betta is a common first choice thanks to its small profile, reliability and low cost. The heater is constantly running, meaning it works best in houses with a consistent temperature. The Marina Betta can keep tanks up to 1.5 gallons warm in most houses, less or more depending on the rooms temperature.
Most issues seen with this heater are when people keep the tank in a room that gets far too hot or cold occasionally. This heater is not designed to adjust to changes like that. Only use constant heaters in rooms that are kept a consistent temperature.
Unlike most aquarium heaters, the Marina Betta can also be buried underneath the substrate. This is thanks to its always on nature. What usually happens when you bury heaters is they heat the substrate around them before the heat is then transferred into the water, keeping the heater extra warm. While other heaters thermometers will incorrectly read that the tank is too hot and turn off, the Marina betta will keep going. This does mean, however, that you should keep your own eye on the tanks temperature when first putting the heater into place. Additionally check the tanks temperature when the houses heat changes. You may need to add a timer to this heater to have it working part of the day during hotter seasons.
#2 Tetra HT
The tetra HT is my second choice for small aquarium heaters for a couple of reasons. First off it is one of the smallest aquarium heaters to come with an electronic thermostat, keeping your tank from getting too warm and harming the fish. The lack of temperature control is a great feature when your tank will be around children who want to touch the aquarium. It’s sleek design makes it easy to hide in the tank and the low cost makes this a low commitment heater.
That’s not to say the heater is low quality. The Tetra HT will almost always last over two years. Some people will go the safe route and replace it every year, but I find the excessive. Just keep a thermometer on the tank, check it every day or two and your tank will be fine.
There are some close competitors like the Hydor Theo Which works similarly and has a controllable temperature, however the cost is a bit higher and the heater is much harder to hide in the tank. If you can manage to hide the Theo you can certainly consider it, but I much prefer the simple look and no temperature adjustments of the Tetra HT for small aquariums that are fine at 78°.
The Two year warranty is a nice add on for this low cost aquarium heater. More often than not, as long as you are friendly and have your purchase info on hand, Tetra will be more than happy to help you out even past the warranty.
#3 Hydor Slim Aquarium Heater
The Hydor slim heater functions much like the Marina Betta. It runs constantly and does not have a shut off mechanism. The flat design of the Hydor Slim does take up the least space of any small aquarium heater. Place a few small rocks or substrate on top of the heater and it will stay in place, even in tanks with powerheads running.
The cord Measures out to be just over six feet, letting you place the tank wherever you like. Hydor does back this small heater with a two year warranty. Just be sure to keep track of the proof of purchase, as you will need to send that in along with the heater to have it repaired or replaced. Remember you will need your own shipping box for this particular heater, so either keep the box on hand or use another similar sized one in its place. I personally keep a few boxes compacted in the closest incase any of my household appliances happen to break down. Always nice to have some boxes and they can be a bit costly depending where you live.
#5 EHEIM Jager Aquarium Thermostat Heater
While I much prefer this heater in larger tanks, the Eheim Jager is simply so efficient, safe and reliable that I cannot ignore it. It is a bit long for most small tanks, however if you can fit the nine inch heater into your tank I highly advise you do so. Keep in mind the temperature display is Celsius only, but this only takes a minute or two to convert to Fahrenheit if you need to.
The simple design relies on their unique lab created glass that allows the Jager to transfer heat more efficiently than any other heater while still being nearly indestructible. Despite it being at a minimum of 50 watts, it still costs less to run the Ehiem Jager than any other heater. Couple this with the thermo safety control and you can make your small aquarium much cheaper to maintain while also removing any chance of cooking your fish. The only big draw back is the size.
#6 Aqueon Pro Heater
A consistent supplier of excellent craftsmanship, Aqueon has set the standard with this low cost and highly reliable submersible aquarium heater. The heat reads in Fahrenheit and is perfectly consistent but runs 1 degree cooler than what it is set to.
The Aqueon features a life time warranty.Usually equipment will breakdown right when the warranty ends. Aqueon is one giant step above the rest of the competition here, allowing owners repairs and replacements whenever they need them.
A long warranty does not mean faulty equipment. The Aqueon Pro Heater actually has several new safety features you wouldn’t notice until something went wrong.
- The heater automatically shuts off when removed from water, restarting when submerged in water. No risk of burning your hands when moving the heater around.
- A no glass design keeps the heater from shattering from small drops and quick temperature changes.
- 5 Sizes, one of which is 50 watts, allows us to fit this high quality aquarium heater in small tanks.
| Room Temperature | 50 Watts | 100 Watts | 150 Watts | 200 Watts | 250 Watts |
| Cold Room (68° F) | 14 Gal | 19.5 Gal | 37 Gal | 52.5 Gal | 60 Gal |
| Normal Room (73° F) | 17 Gal | 25 Gal | 46 Gal | 64 Gal | 75 Gal |
| Warm Room (78° F) | 20 Gal | 30 Gal | 55 Gal | 75 Gal | 90 Gal |
While we are focused on the 50 Watt, it’s nice to see how consistent the heater is in larger sizes. While you may have noticed the tank sizes it can cover are well above small tanks, this is not an issue. The heater shuts down automatically when the tank reaches the desired temperature. This means, unlike always on heaters such as the marina betta, the Aqueon pro will shut down when the room gets warm and the tank does not need heating. A really valuable trait for those of us with unpredictable weather.
Be sure not to bury the heater in gravel unless you really know what you’re doing. This will cause the heat to stay around the heater, keeping its thermometer from working properly. Usually this will result in the heater running far less than it should, keeping the tank cold.
For setting the heat a standard turning knob is located at the top of the heater, complete with number readings to show you where your water will be heated to. Underneath the rim lies the red/green indicator light that switches on, green, and off, red, signaling when the heater is in use.
As this heater is designed to be used in tanks with strong water flow, its suction cups will not fail. I find this to be a big pro. Any extra time I have to have my hand in the small tank is time spent adding oils and waste to the tanks small ecosystem.
Niche Bonus: Hydor’s Inline
The Hydor Inline aquarium heater is the best possible option for small aquariums as it does not go inside the tank. However it requires some form of water movement outside of the tank. Inline aquarium heaters work by passing water through the heater, heating the water as it is moved through the system. The heater continues to run until the tank hits the right temperature and shuts off, becoming a fancy looking part of the tubing.
Creating a water system isn’t difficult. It could be something as complex as a sump, central water system for multiple tanks or even something simple like a Canister Filter. As long as there is tubing with water running through it to the tank regularly, the Hydor Inline aquarium heater will keep the tank warmed.
Here are a few of my favorite features for the Hydor:
- It comes complete with a two year warranty
- The average lifetime is over three years
- It is incredibly efficient, both energy and heat distribution wise
- Works for all tank sizes
- Extremely durable with powerful connections to prevent leaks
The only major downside is that this heater only comes in 200+ watt sizes. This does, however, make it much cheaper to move to a larger tank if you choose to do so. I know I got my first 50 gallon only a few months after a 10 gallon.
The installation is quick and easy, just connect the tubing to both ends and tighten the red knobs on the top and bottom of the heater. These bite down onto the tubing, making a powerful connection that won’t weaken over time.