I have had tanks my whole life. I recently started up a 12g nano reef with an open top. I soon realized how much water evaporates from an open top talk. I do weekly water changes, but after adding so much top off water it got me thinking. Is doing close to 3 gallons a week of top off water enough to not have to do water changes? Or does evaporated water not carry harmful stuff like nitrates and ammonia?


