Betta With Fin Rot

[Queen Bee]

I've had Charlie in the same 2 1/2 gallon tank since July. It is heated and has an underwater gravel filter. Water changes are done weekly. Last sunday, I did his water change as per usual (90%) and cleaned the tank. Four days later, I noticed his fins were very sad looking. The top fin is almost completely clamped together. I dosed with primafix for 7 days, did a 25% water change and added a little bit of salt to the tank. I do have it divided and a small female on the smaller side. Ruby's fins are clamped together as well. I noticed no change in either of the fish. They are no worse, but no better either. Should I switch the medication to melafix? I really like the jungle medications, is there something they have that will work better. Both fish are still eating and only active if I am near the tank and trying to get their attention. Otherwise, they just lie at the bottom. What should I be doing now?

 

[LauraFrog]

Is there any ammonia showing?

Do you have any other tanks that were water changed within a day of this one and are those fish all fine (to rule out contaminated water supply)?

Is the tank covered? Has anybody sprayed anything (toilet deodoriser/air freshener/deodorant/perfume/insect spray/cleaning spray) in the room the tank is, or nearby? Has anybody burned incense or has there been smoke in the kitchen?

I ask this because of something odd that happened to a whole tank full of platys. I changed the water after rain and some runoff - probably fertiliser or pesticide - had gotten into the water. They were all practically paralysed, they all lay on the bottom with clamped fins and refused to move or eat anything. I was totally at a loss and they did that for a week. I thought I would lose them all, but then I got some uncontaminated water, did a 90% water change, and within an hour they were all back to normal.

 

[Queen Bee]

I do the water changes for all my tanks at the same time. Same water is used for the other 2, and all fish in those tanks seem fine. (One has female bettas in it)

Never tested ammonia since I change most of the water. Doing changes and tests today, and will test the problem tank as well this time.

I never spray anything in the room, it is off of the kitchen, but I rarely cook. I am guilty of burning scented candles alot though.

Again, everything I do is the same as I've done since July when I got him. Been feeding blood worms these last couple of days to give him some extra vitamins. Still showing the betta appetite.