Types of Aquarium Thermometers

Aquarium thermometer
Sean Murray / Flickr / CC By 2.0

Aquarium thermometers are a small item, but they have a significant impact on your aquarium. Although the tank may look fine, changing or unsuitable water temperature can have a negative effect on both fish and plants. Having a good thermometer and tracking water temperature at various times and days will help you identify and correct problems due to temperature changes.

There are three basic types of aquarium thermometers: stick on the outside; float/standing in the water; and digital meters....MORE Each basic type has several subtypes with their own pros and cons. Various thermometers are better suited to different styles and sizes of aquariums. Regardless of the type you choose, we recommend using a thermometer for every tank. Record temperatures regularly to ensure the aquarium water temperature is stable and in the optimal range for your fish.

  • 01 of 03

    Stick On (LCD) Thermometers

    Aquarium stick on thermometer
    Amazon.com

    Stick on thermometers are the most widely used thermometer in freshwater aquariums; they are often provided as part of the new aquarium package. They are usually referred to as LCD (Liquid Crystal Display) thermometers and sometimes called "digital" thermometers, which is not fully accurate. Although some may have what can be termed a digital display, the thermometer is not truly a digital one. When looking for thermometers, particularly online, make sure that you aren't sold a...MORE common LCD stick-on thermometer in the place of a more expensive digital thermometer.

    LCD thermometers are accurate enough for general use, versatile, easy to use and inexpensive. Many have dual Fahrenheit and Celsius scales, while some have a single scale in larger numbers. The range also varies from model to model, which isn't a big issue for general use. Most are designed with a vertical scale, but a few horizontal ones are available. There is some debate regarding the effect of the room air temperature on these types of thermometers, as they are located on the outside of the tank and can be impacted by the air temp. This is generally not a significant issue, with the exception of cases in which the ambient room temperature is much lower than the aquarium water temperature. In these cases, the LCD thermometer may read several degrees lower than the actual temperature of the water.

    When using LCD thermometers, there are a few tips to follow.

    1. Do not place them in a location where they will receive direct sunlight, or are near a heating or cooling vent. Aquariums should not be placed in such locations anyway.
    2. Do not place the thermometer below the gravel level, as the reading will not be as accurate.
    3. Lastly, the thermometer reads best when viewed straight on, so place it accordingly. If you have to contort your body just to see the thermometer, it's not in an ideal location.

    Pros

    • Inexpensive
    • Easy to apply
    • Can be placed in multiple locations
    • Unbreakable

    Cons

    • Can be hard to read in low light
    • No alert feature
    • Less accurate than digital
  • 02 of 03

    Floating or Standing Thermometers

    Floating aquarium thermometer
    Amazon.com

    Floating or standing thermometers are placed inside the aquarium, giving a more direct measurement of the water temperature. There are several styles, including ones that stick to the inside of the tank with a suction cup; those that hang on the inside with a clip; others that simply float around in the water; and models that are weighted so they sink and stand on the bottom of the tank.

    Possibly the biggest downside of these type is the fact that most are made of glass, and thus are breakable....MORE If your tank has large boisterous fish, this is not a wise choice for a thermometer. Another negative is that the scale is often in smaller print than other styles of thermometers. This is offset by the fact that many have a colored "safe" zone imprinted on the thermometer that allows for a quick visual temperature check. Like LCDs, these can be placed wherever needed, and in the case of large tanks, multiple thermometers may be used at either end of the tank. The standing models sink, which allows for a temperature reading near the bottom of the tank.

    Pros

    • Inexpensive
    • Can be placed in multiple locations
    • Not impacted by ambient room temperature
    • Many have easily viewable "safe" zone

    Cons

    • Breakable
    • Scale may be small and difficult to read
    • No alert feature
    • Less accurate than digital
  • 03 of 03

    Digital Thermometers

    Aquarium digital thermometer
    Amazon.com

    Digital thermometers consist of a probe that is placed in the tank, either permanent or temporarily, which in turn connects to a digital display outside the tank. Some connect wirelessly, while others have a cord that physically attaches the probe to the display. Generally, these models require batteries to operate, although a few high-end models plug into the wall. The sensor probe is usually attached to the display, which can be unsightly. A few models place both the sensor and display placed...MORE inside the tank. With these, there is a risk of battery leakage in the tank.

    Some models provide an audible alert feature that will sound an alarm when the temperature falls below or above the desired range. Most lower priced models do not provide an alert, nor do they display in more than one scale. When choosing a style, check the probe cord length, as it varies from model to model. As with other types of thermometers, the temperature ranges that can be read also varies. Keep in mind that although these models are usually fixed in one spot, you can easily move them to take a reading in a problem area of the tank.

    Pros

    • Reading can be taken in any location with a single meter
    • Not impacted by ambient room temperature
    • Unbreakable
    • Digital display is easy to read
    • Some have alert features when temp is out of range
    • Generally most accurate type

    Cons

    • Most expensive type
    • Most require batteries to run
    • Usually more expensive