Automatic water change.

I know it's a lot of fun thinking of how to build equipment to carry out various technical functions. If I was going to build an automatic water changer, I would keep it as simple as possible by using only municipal water, unless there was some problem with its composition. Once the plumbing had been worked out, I would then calculate the gallons per day that I would be adding. To detoxify the chlorine and chloramines, you will have to devise a method of adding something like Amquel to the tank or sump each day. In my view, there are two ways of doing it: The first way is to wake up each morning and manually add the dechlorinator to the tank. In this way, it's there, in the tank, waiting to bind to the day's incoming chlorine and/or chloramines. The second way is to install an aquarium doser. Personally, I would add it manually, but I know this is not as technically cool as a second piece of equipment. Finally, you must select a dechlorinator that will NOT bind to ammonia and nitrites....otherwise, it will be consumed before it can bind to the chlorine and chloramines. For what it's worth.