The Slim heater will increase the water temperature of mini aquariums up to 10 gallons by a few degrees compared to the ambient room temperature. The Slim heater can be used in glass, acrylic, plastic fish bowls and aquariums. Safe to use under gravel. Please note, Slim heaters are not suitable to be used in environments without water Extra small slim heater is a great choice for Betta fish & suitable for fish tanks 2 to 5 gallons, measures 5.4L x 2.5W inches, 7.5 watt; Plug and Play universal fish tank heater; No temperature to set; slim heater provides warmth for betta fish without taking up much room Heater can easily be placed submerged in water or even under the tank gravel; The 90 degree angle makes this great for Betta acquariums; Safe to use in glass, plastic and acrylic fish tanks Plug & play universal fish tank heater, the slim fish tank heater can be used in both fresh or saltwater environments Easy to hide fish tank heater is ideal to use for betta fish, gold fish and glow fish