Aquarium thermometers are an inexpensive necessity - always use one to avoid an outcome of your aquarium water being too high or too low. Indoor temperatures fluctuate by time of day and season - even when monitoring your aquariums temperature with the thermostats on your central air, aquarium chiller or aquarium water heater, something can go wrong. It's better to play it safe and have that aquarium thermometer
so you'll know of any drops or rises in temperature immediately. Aquarium Thermometers and Digital Aquarium Thermometers
are hardy, reliable devices you can entrust with the safety of your aquarium, make sure to pick one up if you don't have one.