Maintaining the right water temperature is one of the most critical parts of fishkeeping. Whether you keep freshwater guppies, tropical tetras, or delicate marine species, even small fluctuations outside of their preferred range can lead to stress, disease, or worse. Most aquarists are familiar with the classic glass stick-on thermometer or a submersible digital probe, but in recent years another tool has gained popularity: the temperature gun thermometer, also known as an infrared thermometer.
These handheld devices look a bit like a radar gun or cordless drill, and they allow you to quickly measure surface temperatures without dipping anything into the water. But how accurate are they for aquariums, and what’s the right way to use them? Let’s dive in.
What Is a Temperature Gun Thermometer?

A temperature gun thermometer is a handheld device that uses infrared (IR) technology to measure the surface temperature of an object. Instead of requiring physical contact with the water, the gun detects the infrared radiation emitted by the surface and calculates the temperature.
- How it works: Every object above absolute zero gives off infrared radiation. The thermometer’s sensor reads this energy and converts it into a temperature reading.
- Design: Most models have a pistol-like shape, with a trigger to activate the reading and a small digital display showing the temperature.
- Features: Many units allow for switching between Celsius and Fahrenheit, adjustable emissivity (important for accuracy on different surfaces), and laser pointers to help you aim precisely.
In other words, it’s a quick, no-contact way of checking temperature—similar to what chefs use in kitchens, mechanics in garages, and HVAC technicians in homes.
Why Use a Temperature Gun for Aquariums?
At first glance, an infrared thermometer might seem like overkill for an aquarium. After all, we’ve had floating glass thermometers for decades. But temperature guns actually bring a few unique advantages:
- No Contact with Water
You don’t need to dip a probe into the tank or suction a thermometer to the glass. This eliminates the chance of contaminating the water or introducing soap, oils, or other residues from your hands. - Instant Readings
Unlike glass thermometers that can take a minute or more to stabilize, an IR gun gives you results in less than a second. This is especially handy if you’re monitoring multiple tanks in a fish room or fish store. - Multiple Tank Use
A single infrared thermometer can be used across multiple aquariums without moving equipment or adding a thermometer to each tank. - Detecting Hot and Cold Spots
Infrared guns let you scan different areas of the glass and even the water surface to identify temperature gradients. This is especially useful for large aquariums, paludariums, or tanks with complex aquascapes that may not circulate evenly. - Versatility Beyond Fishkeeping
Many aquarists use them not only for tanks but also for checking reptile basking spots, room temperatures, aquarium lighting fixtures, heaters, and even pond surfaces.


The Limitations of Temperature Guns
While useful, IR thermometers aren’t a perfect replacement for a traditional aquarium thermometer. Here’s what you should know:
- Surface Temperature, Not Water Temperature
Infrared thermometers only measure the temperature of the surface they’re aimed at (usually the glass wall or water surface). This can sometimes differ slightly from the actual water temperature deeper in the tank. - Accuracy Depends on Emissivity
Glass and water reflect infrared energy differently. Some cheaper models may give readings that are a degree or two off unless you adjust emissivity settings. - Lighting Interference
Strong aquarium lights or direct sunlight hitting the tank surface can affect accuracy. - Best for Spot Checks
While excellent for quick checks, an IR thermometer doesn’t provide continuous monitoring like a digital probe or controller. You’ll still want a permanent thermometer in the tank.
How to Properly Use a Temperature Gun in an Aquarium
Using a temperature gun for your aquarium isn’t complicated, but following a few best practices ensures accuracy.
1. Aim at the Right Spot
- For glass tanks, point the thermometer at the side glass just below the waterline. This gives you a good representation of the water temperature since glass quickly conducts heat from the water inside.
- For open-top tanks, you can also aim directly at the water surface. Avoid rippling areas caused by filters or bubblers, as movement can skew readings.
2. Keep a Consistent Distance
Most infrared thermometers list a distance-to-spot ratio (e.g., 12:1). This means for every 12 units of distance, the thermometer measures a 1-unit-wide area. Holding the gun too far away will average too large a surface, reducing accuracy. For aquariums, 2–4 inches away is usually best.
3. Minimize External Interference
Turn off strong overhead lights if possible, or shade the area you’re measuring. Bright lighting can sometimes warm the glass surface more than the water.
4. Compare with a Standard Thermometer
When first using your IR thermometer, cross-check its reading with a reliable in-tank digital or glass thermometer. This gives you a baseline of how accurate your gun is with your specific aquarium setup.
5. Use It as a Supplement, Not a Replacement
Think of your infrared thermometer as a diagnostic tool. It’s great for double-checking temperatures across multiple tanks or spotting differences, but you should still keep a permanent thermometer in each aquarium for constant monitoring.


Practical Scenarios for Aquarium Keepers
Here are a few situations where a temperature gun can be particularly handy:
- Fish Room Management
If you maintain a fish room with 10, 20, or more tanks, walking around with a single IR thermometer is far faster than checking each tank’s individual thermometer. - Troubleshooting a Heater
If you suspect your aquarium heater isn’t working properly, use the gun to measure different areas of the tank. A noticeable difference between one side and the other may indicate poor circulation or a failing heater. - During Water Changes
When preparing new water, you can quickly confirm the bucket’s temperature matches the aquarium’s temperature to avoid shocking your fish. - Aquascaping or Large Displays
In aquariums with rocks, caves, or deep aquascapes, an IR thermometer helps spot-check surface temperatures of decor that might retain or reflect heat differently than open water.
Choosing the Right Temperature Gun for Aquarium Use
If you’re shopping for a temperature gun thermometer, here are some features to look for:
- Accuracy: Look for models with at least ±1 °C (±2 °F) accuracy.
- Adjustable Emissivity: This helps ensure accurate readings when aiming at glass or water.
- Backlit Display: A must-have for dimly lit fish rooms.
- Temperature Range: Most aquarium applications don’t exceed 30 °C (86 °F), but it’s handy if the gun can measure cooler and hotter extremes.
- Durability: Since fishkeepers often use them near water, a model with some splash resistance or a protective casing is a smart choice.
Final Thoughts
A temperature gun thermometer isn’t a replacement for your standard in-tank thermometer, but it’s a powerful supplementary tool for any aquarist. It allows for quick, no-contact checks across multiple tanks, helps troubleshoot heating issues, and gives peace of mind during water changes.
When used properly—aiming at the right spot, keeping a consistent distance, and verifying accuracy—it can save time, improve consistency, and help you maintain the stable environment your fish need to thrive.
Whether you’re running a single betta bowl or a full-blown fish room, an infrared thermometer deserves a place in your aquarium toolkit.