There are several strains of columnaris, and some can be almost impossible to get rid of, as you are finding.
I would euthanize the fish, not take the risk of spreading it to other tanks.
Throw away the plants, sterilize (chlorine bleach) everything that can tolerate bleach. Probably throw away the substrate. If the substrate was gravel or sand it could be bleached, but gravel and sand are so cheap why bother? Soil or any porous substrate is not so easy to deal with. You could bake it, but it smells terrible.
I would euthanize the fish, not take the risk of spreading it to other tanks.
Throw away the plants, sterilize (chlorine bleach) everything that can tolerate bleach. Probably throw away the substrate. If the substrate was gravel or sand it could be bleached, but gravel and sand are so cheap why bother? Soil or any porous substrate is not so easy to deal with. You could bake it, but it smells terrible.
