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Common Diseases of Bettas & Goldfish

Individual Disease Pages

  1. Dropsy
  2. Mycobacterium marinum (Fish TB)
  3. Aeromonas Bacteria
  4. Columnaris
  5. Parasites 1
  6. Parasites 2
  7. Megalocytivirus

Advice and treatment for the most common betta diseases

Most of the diseases bettas suffer from are caused by poor water conditions. With regular water changes, and a suitable environment and you are unlikely to have many problems with disease.  In the event that disease does occur it is best to be prepared with knowledge and to keep some medications on hand. it is too late to order when you need them.
With all disease disinfect all nets and equipment to ensure cross contamination does not occur.
All new additions to your betta tank, plants, snails or other fish, should be quarantined for at least 3-4 weeks before adding them to an established  healthy tank.

First Things First – How to Mix Tablets

The following video shows how to make non-soluble tablets mix into your tank water without lots of floating bits.

The following paragraphs will be expanded into pages soon

Fin Rot

Fin rot is a fairly common disease in bettas and once it affects the body it can kill. It is identified by the fins having pieces missing and a raggedy appearance. Sometimes the edges of the fins can be edged in white, red or black.
Dirty water is one of the main causes of fin rot. Sometimes damage caused by nipping can also allow bacteria to take hold. It is a contagious disease, so if you have a shared system all your bettas will need to be treated whether they are showing symptoms or not.

Treatment: Use an anti-bacterial medication, and IAL (Indian Almond Leaves) as they have anti-bacterial properties.

Once treated your bettas fins should grow back, although they will not always look the same as before.

Fin Melt

Fin melt is an extremely aggressive form of fin rot where the fins appear to melt. This requires urgent treatment with strong medications.
Treatment: Tri-Sulpha (Blue Planet) or Triple Sulpha (API Pro) are readily available, Tetracycline is also recommended.

Pinhole Fin Rot

Pinhole fin rot is similar to normal fin rot, but manifests as small pinholes in the fins.

Treatment: Is the same as for fin rot.

Lymphocystis & Tumours

Lymphocystis (sometimes called cauliflower disease) is a viral infection and is highly contagious.  It causes unsightly growths on betta and other aquarium fish. Sometimes these growths appear and then disappear, a little like a cold sore does on humans.  Others can remain permanently. growing larger, and on occasion dissolving and regrowing.  Tumors can also be common especially on Dragon scale and Metallic scale bettas. These look similar to Lymphocystis. Neither are usually fatal unless in a bad position like the gill, or unless the fish has a lot of growths.  It can leave a large hole that is open to infection until it heals if it does slough off.
Here is an example of a betta with a tumour/ lymphocystis type growth towards the rear on one side :

Bettas with this condition should not be kept in shared systems or sorority tanks as it is difficult to determine if it is a non-contagious tumor or lymphocystis.


Velvet is an extremely contagious parasite.
It is identified by shining a torch on your Betta and looking for a fine dust-like covering that can
appear gold, rust coloured or grey.
Symptoms include clamped fins, lethargy, flashing ( scratching themselves against objects) loss of
appetite and sometimes loss of colour. This disease is deadly if not dealt with quickly.

Treatment requires breaking the life cycle of the parasite.
Velvet infects the gills before the body so flashing and rapid breathing may be the only obvious first

As well as feeding off the host fish the parasite is photosynthetic and requires light to survive.

Velvet has a four-stage life cycle.

  1. Is the feeding stage, during which the trophonts live in the epidermis of the fish absorbing
    nutrients and where they photosynthesise. This stage lasts approximately six days in tanks with tropical
  2. Upon maturity the trophonts become what is known as tomonts, they break through the skin of the fish
    causing damage that lends itself to further infection.
  3. The reproductive stage in the water is where the tomont divides to become up to 256 dinospores.
  4. The dinospores now look for a host and will die if they do not find one within two days in warmer water temps.

NB. Colder temperatures slow down the life cycle

Treatment: I recommend Blue Planet Multicure

Active Ingredients:
Malachite Green 0.40mg/ml
Methylene Blue 4.00mg/ml
Acriflavine 2.00mg/ml

5 drops per 1 liter or 5ml per 20 liters.
For sensitive fish (Loaches and Catfish) use at half this dosage.

Take care not to overdose. This kills the parasite but only in the free swimming stage.

Repeat treatment after 3 days. 3 x treatments.

Cover the tank and keep dark.

The Salt Method
Velvet can be treated using salt, heat and darkness. Although there are salt resistant strains emerging. I personally would use a medication.
1. Raise the temperature in the tank slowly to 28C-30C to speed up the life cycle of the parasite.
2. Dissolve salt before adding to tank using warm de-chlorinated water in the ratio of 3 level teaspoons (1 x level tablespoon) of aquarium salt for every 5 litres of water in your tank.
3. Add this slowly over a period of hours to give your fish time to adjust to the salinity.
4. Black out the tank by turning off the lights and covering with a blanket or towel.

Keep your tank like this for at least two preferably three weeks. When feeding keep the exposure to light down to a few minutes at most.

Once treatment is complete, so a number of water changes to reduce the salinity.

Quarantining fish for 3-4 weeks will keep velvet out of your tanks.

Fish that have previously been exposed to Velvet can gain some immunity even where the parasite is existing, but if placed under stress an outbreak can result even though no new fish have been added; leading to the impression that Velvet is ‘seasonal’ or ‘in all tanks all the time’. Proper treatment will eradicate it.

Make sure your nets/equipment are disinfected!

More to come.