Small Fish Tank Heaters

fish tank
aquarium: a tank or pool or bowl filled with water for keeping live fish and underwater animals
Fish Tank is a 2009 British drama film directed by Andrea Arnold. The film won the Jury Prize at the 62nd Cannes Film Festival. It also won the 2010 BAFTA for Best British Film.
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.

heaters
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 person or thing that heats, in particular a device for warming the air or water
(heater) fastball: (baseball) a pitch thrown with maximum velocity; "he swung late on the fastball"; "he showed batters nothing but smoke"
A conductor used for indirect heating of the cathode of a thermionic tube
A fastball
(heater) device that heats water or supplies warmth to a room

small
Small items of clothing, esp. underwear
limited or below average in number or quantity or magnitude or extent; "a little dining room"; "a little house"; "a small car"; "a little (or small) group"
on a small scale; "think small"
the slender part of the back