Columnaris aka Flavobacterium columnare is NOT fungus but bacteria, specifically gram-negative bacteria. This bacteria adheres to most parasites, most prominently ich and can infect fish only if the wounds are left untreated or slimecoat damaged thus epxosing the tiny blood vessels to this bacteria.
Dip your plants in 10% bleach solution or potassium permanganate if you are worried about potential carriers of parasites. As far as bacteria is concerned, your primary concern is HOW the bacteria manage to infect the fish through other means, not necessarily the introduction of plant itself UNLESS the plant somehow managed to introduce parasites that injured the fish.
Was the fish injured before?
Any history of parasites?
What fish did you lose?
Any abrasive decors?
For fish infected with columnaris, separate them immediately and make sure hospital tank is cycled already. Add salt at a teaspoon per gallon and be sure to dissolve it. Add another set after 12 hours. Depending on the pH, some antibiotics can work well with alkaline water such as kanaplex (nephrotoxic unfortunately to dropsy cases or cases involving renal damage) or tetracycline for vice versa.
. The question is, the Java Moss that is in the tank will it be a carrier and give the disease to other fish? Or is it "safe"?
