trophical fish

Question
hi
i have a diaster going on in my fish tank. I just bought 4 tiger barb two weeks ago and they were doing fine. I yesterday i notice something strange in those 4 tiger barb. All their tail and fin were little bit rotten up. It looks like their tail and fin bit burned up. I don't know if this is a sign of fin rot or tail rot disase. I also have one more tigerbarb which is about 3month old. his fine and healthy and i don't see any affect on this tigerbarb, just these four. So what i did was i changed about 20% water change, and change my carbon yesterday and today i add full dose of cycle. I hope this work. My tank is established tank about 4 month old, i also have good filter which is aqua clear filter 50 along with airpump. I don't know what's wrong with my tank. If anything happen to these fish, iam thinking about giving up and throw my tank for once in for all, i spent lot of money on these tank and decoration.etc.. I hope you will help please

thank you for your time

Answer
hey jeeva,
it sounds like fin and tail rot, because all of them have it but the one.
go to the pet store and ask a person in the fish department to help you, tell them everything that is wrong and they should get you the best medicine needed to add to your water.
hopefully this will solve your problems, it's awful that your tank is having such difficulty starting off. good luck with your tank.
bets wishes, chelsey