The Hydor THEO Heater line features PTC patented thermal technology which makes it among the safest aquarium heater lines on the market. UL listed by design, not by the use of accessories. Made from specially engineered shatterproof glass which, while not unbreakable, is designed to resist breakage in most normal aquarium situations. Highly accurate due to the use of precise micro-switch technology. For use in freshwater and marine aquariums.
The 25W/50W & 100W/150W models, at 7″ & 8.9″ respectively, are among the smallest sized heaters on the market. The Theo ‘minimum water line’ requirement must be followed for proper operation.