I used it when I initially filled the pond. But not since. I don't do water changes, just top off the pond when the level gets low. I have a lot of evaporation, so it's usually a couple of inches every couple of days. We have a water spicket right by the pond, so I put a splitter on it and ran a short hose under the mulch to the pond so all I have to do is turn on the water to fill. It is above water level though so the water hits the air before it hits the pond. Like someone else mentioned I've heard that gets rid of chlorine gases. And like yours, my fish always rush to the water and seem to really like when I am filling it up. Knock on wood, but haven't had any fish die so far, one disappeared (think a bullfrog ate him), and one got stuck out of water on top of the forget-me-nots, but I saved him in time. We have something in between city and well water. They call it county around here, but basically it's treated water, just not as treated as city water is. Whatever that means. Different water plant I guess.