I'm not sure if it does. I put mine on just to help get the water at the top of the tank moving a bit. I overfilled it during the last water change , the water coming into the tank is not moving the water at the top much. Other than that it is usually just switched on for the axolotl to play with. I put it on again this morning and Jeffrey was lurking in his cave, with in minutes he was hovering over it..2 hours later he is still there.