What am I doing wrong?

Bo was on the mend from Fin Rot. I had treated with tetracycline and he got worse so I 'detoxed' him with twice-treated water that contained epsom salt and daily water changes. After two weeks of fighting the fin rot, he was fie and frisky.

I changed his water less frequently and put a filter on his 2-gallon tank (says 2.5 but two gallon jugs or water fill it up.) The last time I changed his water he seemed really stressed so I floated some Rooibos tea (organic) in the tank for an hour. He got really mellow, but still ate like a little pig.

I cleaned out his tank 100% and looked at him in his betta cup and... his find are stripped to ribbons. I removed the filter and put some tetraycline in the water.

I have Jungle Fungus eliminator fiz tabs (all I could find) and will chop one in half and put it into a 5 gallon jug of water since it treats 10 gallons, but... am I doing something wrong? He was getting better. Now this?

Should I stop the tetracycline and go back to epsom salt (a little over 2 tsp in 2 gallons) or use the fiz tabs? Both? Help!

Here is how he looks: http://www.youtube.com/watch?v=FWbvv91NFUM&feature=youtu.be Sorry for vid, my camera wasn't able to catch him without being blurry.