I just saw this thread. How is your bichar doing?
If it is just the fin i wouldn't worry too much but if you notice more nips something may have started thinking it's a chew toy. If the edges of the nipped area start to turn white I would put him in a hospital tank if you have one available. Since you have such a large tank you probably don't want to try to treat it... I have my guy in a heavily planted 55 gal and through the years have had to treat the tank for various things and added salt, melafix, pimafix or coppersafe either together or separately at one time or another and none of it seemed to bother Spike (my senegal bichar). They are very hardy! Also Spike sometimes likes to float at the top of his tank too, usually in some of the floating plants, i think he's stalking. I sometimes add inexpensive Danios for him to hunt...
