I have been battling some stubborn "fungus," which I am pretty sure at this point is columnaris. During treatments, I have seen improvements, and slowing of the spread, but not a complete cure. So I'm trying Furanase along with salt and increased aeration now. One of my swordtails has mouth fungus on his bottom lip, and since treatments have failed to completely cure him, about 1mm of his bottom lip is already gone. He can't close his mouth anymore. So many of the fish have it, I moved them all into my 29g for treatment. After treatment they will be seperated again between my 29g and 30g. The bottle instructions suggest 3 days of treatment. Today is the 5th day, and while I see improvement in some of them, it's not gone yet. Does anyone have any experience with this med for treatment stubborn fin/tail rots and cotton mouth? How long would you continue treatment before giving up on this med? Monday is PWC day. I think I'm gonna do a huge PWC and redose to continue treatment for several more days. Treatments I've already tried: Jungle Fungus Clear Maracyn/Maracyn 2 Salt Peroxide applied directly to effected fins Pristine water conditions... 50%pwc weekly, and nitrates never get above 0 due to plants. If it's possible for this to spread from one tank to another by using the same gravel vac on all tanks, then that's why fish in all tanks have been effected. My poor CT betta's fins look bad. He's in a 10g alone with great water, plants, and very light feedings. He still builds the occasional bubble nest, so I don't feel he is stressed. I just don't understand. Casualties so far: 1 harlequin rasbora. I've been fighting this for months now. I'm surprised I've only lost 1 fish so far.