Updates: The fish eventually stopped fighting. I am not sure what changed. Temperatures may be slightly lower in the new location, but other than that I have no idea what happened. One day they started fighting less, and eventually I did not have to put up the screen to separate them. They have been together for a year now. They do occasionally have very mild brief conflicts, when I do water changes and the volume of water is lower and the territory gets smaller. As soon as the tank if full again they go around their business. In any case, I am planning to make a pond 
