Once I get rid of all of all my female guppies, I will have an empty tank. I plan on switching it back to freshwater once they are gone. I want the tank to have a single fish. I know I could probably do a goldfish (as long as I keep on top of the water, thinking 50 percent change 3 times a week), which would be fun. What are my other options? I am willing to soften with distilled water or harden with buffering salts as necessary. Ideas?
