I have had my betta in the same 2.5 gallon tank, with the same plants for over two months now and have never noticed any damage to his fins. I recently did a 100% water change on his tank to clean it after leaving for vacation. I was out of town for a day and left my girlfriend to feed him just yesterday. I returned today to his seemingly happy, nest well taken care of and his water at 79. Upon taking a closer look I noticed that his bottom fin seemed to have 2 long runnin slits in it. And his top fin is bearing a slight resemblence to a crown-tail (with points) but mine is a common red VT. I doubt this was caused by my artficial plants, 2 of which are a soft rubberized plastic and the other is silk, as they have caused no damage before. Is there anything else it could be before I replace the plants?