its light is convenient, but often heated el result is irregular, in a 20L tank only, I wanted to be on the water was 21 ° and no less this winter, I think his was effective, although sometimes the temperature dropped a lot and the other or she was high, not enough current in the pool I think. but for that price the death of our children can be avoided;) it must be adapted to + + high temperatures (26 °) if it holds either horizontally with the 2 cups although sometimes it moves, easy to disassemble and clean ...