Ok this is the electronic diagram of automatic water changes it is a 2 stage description start from the top photo, this is on the stage when timer switches on for a predetermined time to remove the amount of water needed to be changed next one is the aquarium on the the stage with the water on the lower level when fresh water is introduced. There are 2 floater for security reason this floaters will turn on only after the water has lowered enough and will not in case of evaporation.
Bear in mind that when the tank refills again floater will switch off and input will stop
I hope you understand the diagram all comments are welcome
http://www.bellybean.com/~pave/aquar...es_diagram.jpg