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Fin Rot Symptoms and Treatment


From time to time we all have to face the problems of dealing with various diseases and viruses entering our aquarium. Often these are not caused by mistakes that we have made but there are certain instances where we have contributed to the outset of a disease in the fish. Most diseases and viruses can be spotted early on but some make take some time to show their symptoms and when they are obvious permanent damage may have already been done to the fish. We are their carers and it is our responsibility to check the fish on a regular basis so that we can act promptly before such damage does occur.

Sadly one infection that does seem to appear regularly, especially with novice fish keepers is fin rot. This disease can seem to appear overnight but as you get experienced with looking after your fish you can spot the symptoms early and react quicker, thus preventing long term damage to the fish.

Fin rot nearly always occurs as a secondary infection, it can happen when the fish has undergone stress or has injured itself on décor or even the tank glass. Often fish squabbling with each other can bring on this problem, in all of the cases mentioned, the fishes immune system will be weakened thus allowing the bacteria to attack the fish with ease. The bacteria responsible are normally pseudomonas, aeromonas and flexibacter, under normal circumstances they are always present in the aquarium but unable to cause problems with the fish.

Symptoms of Fin Rot

The first sign of fin rot that normally appears on the fish is a whitening of the fin edges, this will be very minimal to start with bit will soon spread over the fin.

The fins will start to fray and pieces of the fin will become detached giving the fish a ragged look, sometimes a white fluffy growth will also appear on the edges of the fin, this is commonly called Cotton Wool infection, yet another secondary infection caused by the fishes weakened immune system.

As the infection increases, red patches will appear at the base of the fins, bleeding will sometimes occur as well. Once the infection has reached this level irreparable damage can be caused to the body of the fish. If the rays of the fin become damaged it is very rare that these will repair themselves also.

Causes of Fin Rot and how to prevent it

One cause of fin rot that is often overlooked is the fish being stressed, this can be cause by several factors. Some species of fish like to get away at times so add hiding places to your aquarium by using artificial or natural décor such as bog wood or rocks. Plants can also serve as potential hiding places especially the broad leaved varieties. Often fish keepers will keep their lighting on for prolonged periods, this can also stress some species of fish.

Poor water quality is the usual reason for fin rot, aquariums require high water quality that can only be maintained by using the correct filtration for you tank, make sure that the filter is rated for the water volume in the tank and that it doesn’t get clogged. Perform regular water changes, I always change at least 10% on a weekly basis, this will keep the nitrates to an acceptable level and remove other nasties that we do not want in the aquarium.

Incompatibility of the fish, always research that the different species of fish that you are keeping are compatible, aggressive fish will intimidate the more peaceful tank mates and cause them stress. Overstocking the tank can also lead to problems, not only with the water quality but also the fish will feel cramped and unable to swim about freely.

Another common mistake fish keepers make is to overfeed their fish, uneaten food will decay in the aquarium. As it decays it will reduce the water quality and add ammonia and phosphates to the water. Both of these can be harmful to the fish and reduce the strength of their immune system. Only add enough food that can be consumed in a couple of minutes, fish only have small stomachs so excess food just goes to waste. With some species of fish you may have to feed them twice a day but keep the amount of food to a minimum. Fish may always look hungry but they are very clever at conning their keeper.

Treatment for Fin Rot

If the onset of the fin rot is well established and all of the above measures have been observed with no avail there are some treatments that can be purchased to help you rid the fish of this disease. As always prevention is always better than the cure but all is not lost even if the fish appear to be in a terrible condition. To help any medications added to the aquarium perform a partial water change and raise the temperature of the tank by a few degrees, this will pay dividends.

A company called Marcel produce a range of medications that can deal with fungus and rotting diseases, these are known as Maracyn, Maracyn plus and Maracyn two. These are very effective and should deal with the problem very quickly.

Tetracycline is an antibiotic that is available in tablet form, these are simply dissolved in a small amount of water and added to the aquarium or dropped directly into the aquarium water, I find that dissolving them first ensures that the medication spreads around the aquarium quicker thus allowing the fish to benefit from it faster.

Melafix is produced by API and is a tea tree extract. It is used to heal wounds quicker and repair the damage to the fins. This is very popular in Europe and is relatively inexpensive to buy as a large bottle can be used for several treatment periods.

Many keepers add salt to their aquariums convinced that this will aid the treatment, I am not a great believer of this as it can cause adverse reactions with some species of fish, most species will be fine but it is a risk that I personally don’t wish to undertake.


Always use the medications as recommended by the manufacturer, make sure that any carbon has been removed from the filters as this will absorb the medication rendering it useless. Medications in the aquarium will reduce the oxygen levels in the water, to aid with this it may be advisable to add an extra airline to raise the oxygen back to where it was.

After completing the course of treatment carbon can be placed back into the filters to remove any excess medication from the aquarium and also perform a partial water change to aid in this.

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