I have a goldfish who's been getting a recurring infection for several months now. I'm not sure what it is, but my best guess would be columnaris. It looks like a white spot that grows on his tail, and if the infection gets bad enough, it appears around his gills as well. I've tried pretty much every medication (antibiotics, antifungal, and anti-parasite). Salt seems to have worked the best, but nothing has gotten rid of it for good, it keeps coming back. I'm currently doing additional water changes and continuing with the salt treatment and it seems to be keeping it from getting worse, but it's not getting rid of it. I'm worried it's developed a resistance to the medication. Is there anything else I can do? Thanks!