Imagine a cold winter day, and suddenly your heater broke. How long would it take before you start struggling with the cold? Now consider the case of aquariums. Fish are sensitive creatures and a suitable temperature must be maintained inside aquariums.
An aquarium thermometer is a must-have to have a thriving marine environment. It’s as important as the Thermostat you’re using at home, so you know its importance.
But it’s not as simple as getting the cheapest thermometer you can find at your local store and sticking it inside the fish tank. Accuracy is a great deal. It is crucial to maintain the right temperature inside the aquarium at all times.
Depending on the species of fish, there may be varied temperature requirements as well. To make your job easier, we have picked the best aquarium thermometers you can buy online right now.
6 Best Fish Tank Thermometers to Buy in 2023
1. Zacro LCD Digital Aquarium Thermometer
 The Zacro LCD thermometer has a submersible probe that can be attached to the aquarium. The main unit is compact and simple. It has an LCD seven-segment display to show the temperature reading.
Below the display is a small slider that lets you set the temperature measurement unit – Celsius or Fahrenheit. A semi-circular button at the top right of the unit is used to power the unit on or off.
Installation is easy. The Zacro aquarium thermometer comes with two suction cups in the box to have a firm grip. Attach the probe inside the aquarium to ensure that it remains submerged in water. The display unit may be attached to the outer wall of the tank as per the user’s choice. The top of the aquarium is an ideal point to attach the display since you’ll notice the temperature whenever you look at your aquarium.
The Zacro LCD thermometer is quite compact measuring 2.17 inches X 1.46 inches – just about the size of a small cookie. The cable is 24.88 inches long, which, in our opinion, is enough since the display unit would typically be mounted near the top of the aquarium wall. The temperature probe is 1.57 inches in length. Zacro’s digital LCD thermometer requires an LR44 battery that comes in the box.
User Review
There are more than a thousand reviews on Amazon, and the overall rating of the product is 4.3, which means customers are generally satisfied with the product.
Aquarium enthusiasts have been using it for several months and have reported no problems with the device. Accuracy is stated to be within one degree of the real temperature, which is very satisfactory, according to the users.
Most customers who have rated it one or two stars feel that the thermometer could have lasted longer for them. For the others, a faulty unit out of the box is the reason for the lowered rating.
Overall, it is a great device for the price tag, and you certainly can’t go wrong with the Zacro LCD thermometer.
PROS
- Compact and uses a small battery
- A long wire connecting the probe and unit
- Displays in both Celsius and Fahrenheit
CONS
- Power supply wire could have been longer
- Reports of some faulty units out of the box
2. JW Pet Company Smarttemp Thermometer
The JW Pet Smarttemp thermometer is for those who prefer simple devices. It is very cost-effective and is quite easy to install without the need for suction cups.
This mercury-free analog thermometer is being offered in two variants – Standing and Non-Standing. The standing variant can be anchored to the base of the aquarium.
Gravel is a fine material to secure the thermometer to the base of the fish tank. The non-standing variant also needs to be submerged in water. This variant can be secured using a magnet on the outer wall of the aquarium which keeps the thermometer in place inside the tank, which makes it a hassle-free installation.
The thermometer itself is about six inches in length. A red-colored liquid rises in the tube to indicate the temperature. The Celsius and Fahrenheit scale occupy the two sides of the gauge. The manufacturer has marked the safe temperature zone as 22 to 27 degrees Celsius, and the thermometer casing is colored green in that range for quick identification. The measurement is accurate within 1.5 degrees.
User Review
Users are satisfied with the ease of use the JW Pet thermometer offers. Easy installation and use are big positives reported by several customers. Since this thermometer doesn’t cost a lot, some buyers use this as a backup in combination with digital thermometers.
Reviews suggest that the product is fragile, and the glass may break if the thermometer is not handled with care. At the same time, these users have been positive that it does not contain mercury. A few users reported issues with temperature measurement.
PROS
- Simple and cheap
- Easy to read and the presence of the safe zone
- Mercury-free
CONS
- Fragile glass
- Lesser accuracy if placed near the heater
3. LCR Hallcrest A-1005 Liquid Crystal Vertical Aquarium Thermometer
The Hallcrest A-1005 is an easy-to-read digital vertical aquarium thermometer. Being extremely thin,it needs to be mounted outside the aquarium. This unit requires no batteries and is easily movable.
The thermometer has a green zone that lights up when the temperature is in the optimum zone – 76 degrees Fahrenheit. The zone below the green is colored blue and glows at a temperature of 74 degrees while the orange-colored zone placed above the green zone indicates a high temperature of 78 degrees F.
User Review
The simplicity, ease of installation, and creative indication of temperature are the top reasons stated by the buyers to get this. Accuracy is reported to be quite good, and the thickness of the aquarium glass is not a problem. Apparently, the Hallcrest thermometer works well with thick glass.
One area of improvement, according to users, is a refined temperature measurement. Some users have indicated that more than one temperature zone glows at the same time, creating confusion.
PROS
- Simple, outside mount, supports thick glass
- Creative temperature measurement
- Battery-free
- Very accurate
CONS
- Overlapping temperature indication.
4. Marina Deluxe Floating Thermometer with Suction Cup
 The Marina Deluxe is a floating thermometer made from glass. Its measurement range is between 30-degrees and 120-degrees Fahrenheit, which is the appreciable range for the aquarium chillers to keep the temperature within an acceptable range.
This analog thermometer is six inches in length and is provided with suction cups to attach to the aquarium walls. A safety zone marked in blue represents the ideal temperature for tropical fish. Above and below the blue zone, you can find narrow bands marked in yellow color to highlight a temperature deviation easily.
User Review
This fish tank thermometer has been reported by buyers as easy to mount and does its job well. Reviews also suggest that it’s a very accurate thermometer. Some users felt that the size was bigger than expected, but then it allows for easier reading. Users report that the blue safety zone has a very dark color tone which makes it difficult to read at times.
PROS
- Cheap and simple
- Accurate
- Color-coded safe zone
CONS
- The dark tone of the blue colored safe zone
5. AUTIDEFY LCD Digital Aquarium Terrarium Thermometer
The AUTIDEFY Digital Terrarium is a submersible probe-type thermometer. It has a clear monochrome LCD that indicates temperature on both Celsius and Fahrenheit scales. It measures up to one decimal place, so even a 0.1-degree difference is detectable.
The box contains the thermometer, the probe, and the battery. The cable length is 97 cm, or 3 feet, which makes it quite ideal to place the digital reader adequately; and the unit requires a 1.5 V button cell. A switch helps toggle between the C and F scales. It is bundled with two suction cups to attach the unit and the probe separately.
User Review
Customers report that the thermometer is very accurate. The enthusiasts have compared the temperature measured by multiple units simultaneously and benchmarked against a room thermometer, and the readings have been found to be accurate and consistent.
Few users warn that placing the thermometer close to the heater could cause an inaccurate reading. Some customers also recommend that the suction cups should last longer.
PROS
- Digital and measures 1/10 degree
- Accurate and consistent
CONS
- Suction cups could be of higher quality
- Should not be placed near the heater
6. American Thermal – Aquarium Vertical Thermometer
The vertical thermometer from American Thermal is a unit that is supposed to be mounted on the outside walls of the aquarium. The thermometer has an adhesive on its back that will help stick to glass and acrylic, and It needs to be mounted vertically.
This aquarium thermometer can measure temperature in the ranges of 66 to 84 degrees Fahrenheit, and the indicators are quite easy to read. Reusability/movability is one of the unique benefits offered by the thermometer from American Thermal as it can be peeled off and stuck multiple times again.
User Review
The thermometer is reported to be accurate and easy to read with big digits. Customers have been very positive about this unit and have also bought multiple units. One of the positive factors working in its favor has been its small size.
Although, some users have reported that multiple colors representing different temperatures glow simultaneously. The reusability of the thermometer is challenged by the strong adhesive.
PROS
- Mounts outside the aquarium
- Small size
- Reusable with peel and paste
CONS
- Multiple temperature indicators glow sometimes
- The adhesive is too strong and may damage the thermometer during reuse
