Alright I just woke up ten minutes ago. I stuck a "new" 1-3 gallon whisper filter into my 2.5 gallon tank (yes, I know, cruel, but I just moved he'll get a new 5 gallon later as well as my other betta). It is heated to 79ºF (both) and I treat it with aquarium salt, an ammonia neutralizer (that is a conditioner), and Fish Protect (for slime coat). I measure everything out carefully.
I did a 25% water change yesterday to both tanks. Astaire (my veil teil) is treated the same way, and is doing great. He's been battling fin rot for a few months (been following forum instructions like the Bible), but is somewhat recovering. Stamps (my $60 halfmoon plakat as displayed in my avatar) is now swimming around sporadically, yet lazily through the tank, and in between his fancy mask is a red patch of scales that is now extremely pale. The luster in his eyes is gone.
I just did a water change because I noticed the water had spiked in nitrates. It was still in the safe range, but I don't know what the hell happened with that filter. It's out now. I have not used any medications in his tank other than the three items listed earlier.
Please help me save my fish my fiancee bought me from Singapore.
**EDIT** What I meant by a "new" filter is that it's been used for the same fish before when I first received him. I had him in a 1.5 gallon tetra master tank to make sure he was alright after shipping. After I was done using it (1 week), I dried out the filter and stored my stuff away. Now I'm starting to think that I'm an effing retard because it should have occurred to me that I could have gotten mildew since then, but no. I smelled the filter and the little cartridge and they smell fine. No there's no carbon dust, I rinse all my stuff.
**UPDATE** He is perking up from the 100% water change. I am not sure what damage I did to him or if this is just temporary. Should I not use a filter? I was gonna get a Tom Aquarium Mini Internal Filter today for both my tanks. I thought filters were good! Dear Fish Jeebus help me ; ;