Hi, I am super upset tonight as I have just gone to feed my beautiful betta and found he is missing all his top fin and a lot of his tail. This has happened over the course of the day as he was fine yesterday. I think the cause is the filter. I had him for 2 weeks in my 10 gallon tank with a low flow waterfall type filter, however he started picking on my cory catfish so I had to take him out. I bought him a 3.5 gallon tank the next day and decorated it with a log to hide in, soft edged gravel and a silk plant and a couple of plastic plants with rounded edges. There is a heater set at 80 degrees and it came with a little filter. I thought the filter flow may be a bit strong, but he was swimming directly in its stream a lot instead of out of the path of it so I assumed he was fine with it. Now today I see lots of his fin is suddenly missing, so I have turned the filter off.
I tried googling fin damage and fin rot, as I want to make sure it isnt fin rot. However people say that comes on slowly. He did have black around the edge of his fins when I bought him, but they weren't ragged and I think they were just part of his colouring? He is red but had black tipped fins. I did notice he has a few paler patches around his face, but think he always had them. Of course if that is a sign of fin rot I may just have bought him with it already. So is it possible if it was fin rot for them to get so bad so quickly? or is it more likely that it is the filter damage? Most stuff I have read said that the bottom fin is more damaged by fin rot, however his bottom fin seems fine it is his top that is totally gone and about 1/3 of his tail...which makes me think the filter is the likely culprit. He seems fine in himself, swimming about near the top of the tank, eating fine.
So what should I do? I have added some aquarium salt. I read online that bettafix is good for these situations so will go buy some tomorrow. However I do not know what to do about the filter. I don't really want to leave the tank unfiltered, is there a way to reduce the flow of it? like duct tape some foam or something over the inflow and outflow? Any suggestions would be fantastic. I tried looking to see if was a low flow filter could use instead but cant seem to find anything for a small tank like that.
Thanks for taking the time to read. If I can find my camera cord I will attach a photo however I don't know where it is at the moment. I feel terrible for my poor fish and am hoping the fins can grow back, he was stunning and now he looks a mess and I am very guilty, I thought I was doing the responsible thing but obviously not, and ignorance is no excuse.