Fin Rot-

If it doesn't come on it's own it will follow quickly after other disease or physical damage problems. Mild forms of the disease are a clear early-warning sign that problems are on there way. Any tiny touch of white or "see- through" on the tips of the fins, especially on the tail, should send us all scouring for the test kits and making sure that the equipment is working correctly.

The problem is easy to spot but it's hard to diagnose the cause. Look for a reddening of the fins, and sometimes the veins leading to the tips of the tail. This is followed by the tips becoming transparent then tinged with white. Reddening and "soreness" then follows and secondary fungal growths attack the wounds.
The tail or fins gradually erode and if allowed to, will retreat right down to the basic stump.

Cause
The actual cause of fin rot is bacteria that are ever present in the water. Your fish can resist this until something stresses them and/or physical damage causes a wound that allows access for the bacteria. But by far the most common cause is poor water conditions,
Treatment
Any outbreak of fin rot should be treated initially by improving the water conditions, with water changes and by any other appropriate means such as conditioners, resins, and ammonia removers, well before treatment. Check that the tank is warm enough. Like wise remove any other identifiable causes of stress, such as bullying fish.
Some old books describe this condition as hard to treat, but once the cause of stress is removed it generally responds well to treatment.
Medications
There are many medications in the market place. Chose are remedy that is best suited to your circumstances. Ask the sales person about their products that are on sale.
Main methods are; To give the fish a salt bath, Use a phenoxyethanol-based proprietary medication.
After treatment you can usually see remarkable re-growth of the affected areas in a few months time. However their is usually a clear scar where re-growth took place.