The trouble with bettas is tank size. You can't use a big tank, and it's difficult to keep a very small aquarium from 'crashing', where the water chemistry gets out of control. I suggest that you get rid of this betta, get another one from a place that doesn't keep them in small cups. Get rid of the filter and do daily water changes.
I find that once a fish gets sick, that's it. 'Medecines' are a
hustle.
The best advice i could give you would be to get a larger tank and start your fish-keeping 'career with a few tetras. Diamond tetras are gorgeous. Finally, don't buy your fish at a chain store. Go for something smaller and privatrly-owned.

hi Kirby,
fin rot is easy to cure if you maintain good quality water. i suggest to use Methylene blue which is used to cure fungus.pull the fish out and try to apply gently ,directly to affected fins of the fish without touching the gills with a small paint brush or cotton, give this treatment a couple of times in a month.i have treated my betta like this which has severe finrot, now it is cured successfully.
let me know any questions

My betta recently developed white spots behind his gills. He wasn't acting his usual energetic self, so I transferred him to a gallon glass jar so I could treat him with medicated water.

A very small pinch of aquarium salt (prevents ice and velvet) and a single drop of a product called 'Quick Cure (by AP) Fast relief for Ick and protozoan parasites'. I had to rinse out the jar with tap water so I also added some declor.

Put in a single plant and a heater (82ú) and he is doing much better. It has only been two days.

I have a 10 gal tank. I prefer reverse osmosis water instead of tap, because it means I can use less chemicals to treat the water. I buy it at the health food store for 29â a gallon. I don't purchase the containers there because I don't want to spend $20.00. Walmart carries them for a lot less.

I've had the RO water tested at local pet store and they said the PH was in exactly the right range. No ammonia, nitrite or nitrate, etc. Some stores will test it for free.
If you ask for help, make sure they know you are treating a Betta, as not all meds are ok for them.

When I change the water I usually heat the new stuff on the stove. I use a digital thermometer to test the water in his tank/gal jar and then test the heated water before adding it. I gently pour the new water into a ramekin held over the tank/jar so I don't stir up the water in the tank/jar too much!

I looked at many, many sites to find how to help mine. He is only one fish, but I like him! Hope this helps. Good luck with your finny friend!

Links that might be useful:

This first link discusses fin rot

velvetdragon.com/bettas/caresheet.html
www.bettatalk.com/betta_diseases.htm
fish-etc.com/knowledge/spirulina-why-you-should-feed-fish

The best thing you can do for a betta with fin rot is good water. I have to disagree with Mercurio that bettas can't have big tanks, and that a sick fish is a lost cause. Fin rot is usually pretty easy to take care of with good water conditions. If you get a bigger 5.5 or 10 gallon, it's much easier to maintain the water quality.

Right now, you have an uncycled tank with infrequent water changes. This means that your fish is sitting in ammonia. When fish poop, they make ammonia, which kills them. After some time, bacteria build up in the filter that converts ammonia to nitrite. Nitrite also kills fish, so another builds up to convert nitrite to nitrate. Nitrate kills fish at high levels (>40PPM) so weekly water changes need to be performed. Because your fish has been in an uncycled tank for so long with bad water quality, he developed a bacterial infection which caused his fins to rot.

If I were you, I'd upgrade his tank to a 5.5 or 10 gallon, then get a good filter. Use Tetra SafeStart, a bacterial additive, to help kick-start the cycle. Stop medicating, and just focus on clean water. Tetracycline is good for bacterial infections, so I'm glad the fish store sold you the right stuff, but medicating when it's not necessary is not good for the fish. If it gets really advanced, medications can help, but until then clean water and maybe some aquarium salt is best (NEVER use aquarium salt for more than 10 days for freshwater fish, as it can cause permanent internal damage. Give at least 2 weeks between salt treatments). Also get a Liquid test kit (API makes a great one) to test your water. While cycling, never let ammonia or nitrite get above .25PPM. If using Tetra SafeStart, never let it get above .5PPM.

In terms of your filter question, I would recommend the AquaClear 20. While it is meant for a 20 gallon tank, I have one on my 5 and 10 gallon and it's great with a baffle.

I hope this helps!

This post was edited by Mel97 on Fri, Mar 21, 14 at 16:33