Hi. I am a totoal novice at keeping a fish and this is my very first Betta. I have had him for about 3 weeks and I have noticed the last few days that his top fin looks like it is disappearing. I got him from a friend that bought him at a pet store and since I brought him home he has moved around to a few different homes until I could get the proper set up going. He has been in his new tank for a week and he seems so happy in there, but I noticed this issue with his fin. Theer is nothing in the tank that could be damaging in the fins-ther is only one plant and it is very soft silk. If you look at th ephotos of the top of his tail it looks like it ihas been torn or is missing in places? I do not remember it looking like this when I first got him-only wihtin the last few days. So why is this happening to his fin? Is this fin rot? What do I do to fix it? Will his tail grow bacK?
-He is the only fish in the tank
-6.6 gallon tank
-very gentle filter and heater (set to 78 but stays at about 74) looking to buy another one
-very active, swims around happily
-super clean water and everything else is maintaned and checked -only planning to make 1x a week 25% water change with the new tank-but haven't done it yet(due for change tomorrow)