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So what do you use to treat it?
  1. Potassium permanganate is highly effective as a dip and tank treatment.

  2. Doxycycline and tetra cycle work well also, but will trash bio filters and should be used sparingly to prevent resistent strain from forming.

  3. High salt concentrations, as in 1 tablespoon/1 gallon water. Watch the fish for signs of stress, and cut back the salt if you see any. Salt does not kill Columnaris, but it can slow it down significantly.

  4. Water changes. The more water you remove the more bacteria you theoretically remove. Concentrate on cleanliness. Columnaris is a substrate bacteria, it thrives on foods and feces.

  5. Increase aeration. Most severe outbreaks occur in low oxygen waters. Avoid increasing water temperature, it's like adding Miracle Grow to a weed.

  6. Do not use a cocktail medication. Shotgun medications cause far more harm than good. A good specific gram negative antibiotic should be used, and all directions followed. Resistance to medications is a growing problem. It comes from using the wrong medications for the wrong time course.

More resources on Columnaris infection:
Addendum 1-- pH
Lowering the pH/hardness may help. There is a well known researcher of columnaris--- Decostere. He published a paper in The Journal of Fish Diseases (1999, 22, 1-11, "Influence of Water Quality and Temperature on Adhesion of High and Low Virulence Flavobacterium Columnaris Strains to Isolated Gill Arches"). This paper was an excellent set of controlled experiments examining the conditions which affect the bacteria's ability to attach to substrate. This attaching is the first stage in a columnaris infection. What the study found was that most of the strains of columnaris are inhibited by salt, and require certain minerals to attach. Remove the mineral and they can't attach well. This was shown for all but the most pathogenic strain. This might explain why pH worked once, but not the other time. Just a thought.

Addendum 2
Symptoms are any of these: yellowish or whitish lesions on the skin, fins, and gills. Usually the area affected looks kind of pale compared to the rest of the fish. To me, it looks like mildew. One of its common names is "saddle patch" because it can cover the fish dorsal and lateral, resembling a saddle shape. Large areas of skin and mucous can be shed as the bacteria secretes a special digestive enzyme where it is attached to the fish.

Aside from the above general symptoms, the best way to identify it is to take a scrapping of the affected area and look at under a microscope and look at it as a wet mount. This bacteria is actually piles up and forms columns that move under the scope - hence the name. This bacteria is a major problem in aquaculture and has been studied pretty extensively. A real good general article is put out by the Southern Regional Aquaculture Center, Pub #479. Download it at

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