Betta Fish Ripped Fins
Hello I am new to the forum so I hope I don't mess anything up lol but I am desperate for advice about my betta fish.
I got him about five months ago. The betta is the only fish in the tank which is a 3-gallon tank with a filter system and heater inside. I used to have plastic fish-tank decor and plants in the tank but I noticed his fins ripped so I took them out and replaced them. Now there are two real potted plants, a moss ball, and a small treasure chest fish-tank decor so he can hide if he needs. I sanded down any possibly sharp edges on the treasure chest and washed it with water before putting it into the tank. He was fine for a while but I noticed his fins started to rip again and are almost as bad as they were when I had all plastic decor. I tried betta fix and it did help but he ripped off the new fin growth.
Also, I know that fin rot is a possibility but the way his fins look is not indicative of fin rot. I especially know it is not fin rot because some mornings, having observed his fins the night before, I notice that they became significantly more damaged overnight.
I've checked the tank over multiple times, even feeling around with my hand and I cannot determine where he is able to rip his fins so often. I take extra precautions to make sure he is not stressed. I clean the tank once a week, removing at least 20% of the water and replacing it with more conditioned water.
If you have any idea what could cause his fins to tear so often, please let me know. It would be much appreciated.