In Line Aquarium Heater

aquarium
a tank or pool or bowl filled with water for keeping live fish and underwater animals
A transparent tank of water in which fish and other water creatures and plants are kept
A building containing such tanks, esp. one that is open to the public
Aquarium is the debut album of Scandinavian dance-pop group Aqua. Although the group had been together for three years under their original name Joyspeed, their only release up to Aquarium was a single called "Itzy Bitsy Spider".
An aquarium (plural aquariums or aquaria) is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants.

in line
being next in a line of succession; "he was in line for the presidency"
Constituting an integral part of a computer program
Having parts arranged in a line
Constituting an integral part of a continuous sequence of operations or machines
one behind another in a line or queue; "they waited in line for the tickets"
awaiting something; especially something due; "people were in line at the checkout counter"; "she was in line for promotion"

heater
A person or thing that heats, in particular a device for warming the air or water
fastball: (baseball) a pitch thrown with maximum velocity; "he swung late on the fastball"; "he showed batters nothing but smoke"
device that heats water or supplies warmth to a room
A conductor used for indirect heating of the cathode of a thermionic tube
A heater is object that emits heat or causes another body to achieve a higher temperature. In a household or domestic setting, heaters are usually appliances whose purpose is to generate heating (i.e. warmth). Heaters exists for all states of matter, including solids, liquids and gases.
A fastball