Just thought I'd share my recent horror with everyone else so knowledge circulates. I shut down my breeding operation because of a slow strain columnaris outbreak nearly a year ago. I decided to slowly rebuild stocking for a personal display and mostly dropped breeding, still breed rabbit snails. Other than a few small displays and aquaponics tanks, I have nothing but bare bottom Qt setups now. The big tank is totally broke down and I have 7 qt/grow out tanks stocked just to restock it when it's finished. Now, the you need to know this scary stuff! I tore down my big display/severum breeder because of a slow strain columnaris crisis that never killed a fish but was there and meant the fish could not be moved. Many, many, many dollars and months of treatments in Qt tanks everything "seemed" cleared. Some fish were sold off to friends and some to a couple pet shops. I kept one tank up and running with 5 Megalechis Thoratica and another running with nothing but ace hardware ammonia. Fast forward 2 months. The 75 gallon tank with only 5 adolescent hoplos was fine until I introduced 8 baby red spot severum that I had Qt'd for 6 weeks in another room. Within 2 weeks I was in all-out outbreak again. Eventually losing most of those fish. The week before that I had finally added fish "two 2-inch gold nugget plecos" to a 20l with a large canister that had been treated with spectrogram with a tablespoon of salt per gallon for 2 months with no fish. A few days later one became stressed "typical pleco white fade" because the slightly larger one was bullying it. I moved the stressed nugget to a 10 by itself. A friend showed interest in the gold nugget that never showed any signs of stress, still in the 20l, a month ago and a trade was made. Today I find out from that friend, the pleco as well as a 3 year old colony of guppies it's in a 120 with have columnaris. This terrible bacteria can survive the recommended treatment with no fish to host on for 2 months in a canister filter. I drove to the local pet store and then the hour south to the predominant fish store in the area because I had sold the unscathed fish from the original outbreak to them. Thankfully no one had reported any problems with the fish they got from me or other gold nuggets that I had gotten from them. I didn't mean to make this so long but I feel I had to be clear as to there is no doubt this was spread from a fishless system that had been treated with powerful antibiotics and was well above the salinity thought to eradicate it.