I am petsitting a friend's betta fish, and I noticed some ragged edges on his fins, and I think it might be fin rot. He was in a little maybe 1/2 gallon tank, so I moved him into an empty 2.5 gallon with clean water and some live plants. I have not added a filter, but I did put a heater in there. I have a few questions:
1) I used to have the heater in a 10 gallon, and it has never allowed a tank to fluctuate in temperature before. The temp in the 2.5 gallon now is fluctuating between 74/74 and 80 degrees. I had it positioned under the filter in the 10 gallon, so I am thinking that the temp in the 2.5 gallon is fluctuating because there is no water movement around the heater. Should I add a (small) filter, just to move the water? I have an extra Tom Mini Internal filter with a spray bar that is fully submersible--Should I put it in?
2) Would aquarium salt help? I heard that 1 tsp per gallon was good for minor cases of fin rot, with daily water changes and redosing each time you do a WC. Does this sound good? Would epsom salt be better?
3) Is there anything else I can do?
Again, to reiterate, he is in a 2.5 gallon tank with 2 anubias, some java moss, and some brazilian pennywort and a heater. I have a filter handy, but it is not (yet) in the tank.
Thanks for your help!