Thermometer Glass Every fish species has specific temperature requirements, so keep an eye on your aquarium with an accurate glass thermometer. The Aqua One Glass Thermometers are a must have accessory for any aquarium. The easy to read thermometers include a high quality silicon suction cup to fasten it in the aquarium. Both models are mercury free for added safety. Features & Benefits Easy to read High quality silicone suction cap Temperature range of 0-500 Does not contain mercury Suitable for: Coldwater, Tropical & Marine