Best Heaters for a 5 Gallon Freshwater Aquarium Fish Tank: Review
Always Use a Thermometer Inside the Tank
No matter what type of heater you ultimately decide upon, you need to always monitor the temperature. Stick-on thermometers that mount to the outside of the tank are recording the ambient room temperature and not the water temperature which can have a very different reading. For the most accurate water temperatures, use a glass thermometer that mounts to the inside of the glass with a suction cup!
Are you considering purchasing a new aquarium heater for your small freshwater tank?
We recently purchased a 5 gallon aquarium which would become the new home for my daughter's Betta fish. While we wanted to upgrade him from the temporary bowl she was using to a larger home, more importantly we knew that with the fluctuating evening temperatures we needed to get him into an environment that included a heater before the water temperature got too low than the tropical temperatures that we needed to maintain.
In the evenings, the ambient temperature inside our home began to drop to about 70 degrees. We rarely use heat in the house as we live in Florida, but in an effort to keep the bowl warmed, we were running the heat at night to maintain a 76 degree room temperature which would help keep the Betta at the lower end of the tropical temperatures he is meant to be kept in. As an additional precaution, we wrapped the bowl in thick towels to help insulate it as much as possible.
While the new tank was cycling, I began researching the aquarium water heater options and was getting even more confused with all that was out there.
There were a few things I knew I wanted in a small aquarium heater:
- Small size
- Internal thermostat
- Low wattage for small tank
Aside from those features, I was clueless. After reading more reviews of different small fish tank heaters than I can remember and after posting on a fish forum without any responses, I set off to the local big box pet store looking for a solution from the advice of the store employees.
Betta Bowl Heaters Can Kill Fish
While companies do manufacture heaters that indicate they are safe to heat small 1-gallon fish bowls, they're not safe. After much research on what could have been a simple solution, I learned that these flat, round bottom heaters can literally fry a fish as can be read in the numerous reviews on sites such as Amazon. Although they may be 7.5-watt heaters, they're not reliable and certainly not for use with a 1-gallon bowl.
How to Determine Fish Tank Heater Wattage Needed
A good rule of thumb to determine what size heater you may need for your small aquarium is:
5 Watts for every 5 Gallons
This is not an absolute rule as different heaters may work more effectively than others, but this will help guide you to finding a heater that is better suited for the size tank you need.
Not All Low Wattage Aquarium Heaters are the Same
Since we were upgrading to the 5-gallon tank, I did not even consider a temporary solution such as the Betta Bowl Mini Heater made by Zoo Med. While companies may advertise they're safe, a heater in anything as small as a 1-gallon bowl is too dangerous for any fish, especially if you can't maintain a tropical temperature. I would not advise using these at all, unless you're willing to sacrifice your fish.
During my research, many of the reviews I read suggested a 25-watt heater. So, I went looking for one at my local big box pet store. What I found was that some 25-watt heater labels indicated they were for up to 5-gallons, some were for no less than 7 gallons, but no more than 10 gallons. It got so confusing and frustrating!
On the market, there are 7.5w, 10w, 15w, 25w aquarium heaters- all indicating that they will work just fine for a tank 5 gallons and under. BEWARE! Not all low wattage heaters are the same!
After looking carefully at all the packaging and sizes and wattages, I picked up a 25-watt heater, a Top Fin® Submersible Aquarium Heater, which, according to the box was advertised for tanks up to 5 gallons. It had an internal thermostat, was adjustable, and fully submersible. It wasn't quite as small I was looking for, but we could have made it work. When the store employee asked if I needed help, I explained what I was doing and she said that the Top Fin® heater I had in hand was too powerful.
She handed me an Aqueon Mini 10 Watt Heater. And, so I gave it a try.
Aqueon Mini Heater (10-Watt) Review
The Aqueon heater was inexpensive enough (about $14) and I had several weeks to try it before the Betta would be added to the tank, so I decided to give it a try.
The features of the Aqueon Mini Heater 10 Watt included:
- Fully submersible
- Thermal safety shut-off
- Preset temperature to about 78 degrees
- Small size - about 8 inches in length
- Rated for up to a 5 gallon tank
The heater came with two mini suction cups that were easily attached. The installation was simple - put it in the tank, slightly push to engage suction cups, then plug it in.
After several hours, the temperature of the water increased from about 74 degrees to about 78 degrees where it maintained most of the time. I installed the heater on the side close to where the bowl with the Betta was and touched the side of the bowl to the side of the tank. The Betta hung out there as he could obviously feel the warmth from the heater through the glass.
This would have been the heater that I kept, except for one small issue. It indicated in the manual that if the ambient temperature reached 78 degrees, to unplug the heater. Since we were still cycling without the fish, we could test what happened when the room temperature increased. Here in Florida, it's not unusual during the winters for us to have outdoor temperatures in the 40s in the morning and 80 in the afternoon. What we found was on the warmer days, the tank's temperature was increasing up to 86 and at night was dropping to about 76-78. The room temperature was about 78 and 69 respectively.
We decided to look for another solution for a few reasons:
- Nearly 10 degree temperature swings in the water on the warmer days
- Someone is not always home in the afternoons when the temperature is much warmer to unplug the heater to prevent the water from overheating the fish
- Concern was also there that someone would forget to plug it back in
In climates where the winter temperature doesn't fluctuate as much and a home is heated consistently throughout the day and night to maintain a comfortable temperature, I believe that this would be a good solution that would work well.
Hydor Theo 25 Watt Heater
With the concern of the fluctuating temperatures using the Aqueon Mini 10-watt heater, I did some more research and even asked a question here on Hubpages. My research and the answer given resulted in a common product - the Hydor Theo 25-Watt heater - an adjustable heater for a 5 gallon tank.
None of our local big box stores, nor any of the several local fish stores carried this, so I ordered it on Amazon.
The features of the Hydor Theo 25 Watt heater include:
- Fully submersible
- Horizontal or vertical positioning
- Auto safety shut-off
- Shock resistant
- Adjustable temperature with 1-degree click graduate scale
- Small size - 7 inches in length
- Rated for 2 to 7 gallon tanks
- On indicator lamp
The tube of the heater is approximately inch in diameter which was thicker than the Aqueon, but it came with two large suction cups that attached to C-clips which, in turn, clips to the Hydor Theo and holds in place in either the horizontal or vertical positions. In my tank, it is installed vertically with the dial completely submerged.
The temperature dial is located at the top end of the tube and stands about 1/2 inch high. It is easy to turn with clearly marked degree increments.
I love that the tube has an "on" light indicator which you can easily tell that the heater is on. I have an internal glass thermometer inside the tank on the right side (about ten inches away from the heater) and I can easily see that the tank is maintaining a consistent temperature.
I originally had it set at 80 which maintained right at 80 except the warmer days which would creep up to 82-84. I've since changed it to 79 which maintains right around 80 no matter what the room temperature is.
I tested this heater out for about a week while the cycling finished and was very impressed with the results. The Betta fish, who was more lethargic in his temporary bowl due to the colder water temperatures, was introduced to his tank and thrives now in his new home. After nearly two months in his new heated tank, he continues to be very active swimming and blowing bubble nests!
I highly recommend the Hydor Theo 25 watt Heater for a 5 gallon tank!
HYDOR THEO 25W
AQUEON MINI 10W
Adjustable 71 - 89 Deg
Preset to 78 Deg
Horizontal or Vertical Positioning?
"On" Indicator Lamp?
Up to 5 Gallons
Control Steady Temp?
Yes. Controls water temp at a steady temp even with varying ambient room temps. Good for climates that may have wide temperature swings during a day leaving inside temps at or around 78.
No. When room temp rises above 78, instructions indicate to unplug as it will continue to heat the water above the set 78 Deg. Best for climates in which indoor temps remain constant.
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