yes, could be that if there are sharp rocksPoor kid! I just went on Dr Google (I also have cory cats and would be worried, too). Could it be red blotch disease? Can be caused by poor water quality or sharp surfaces leading to secondary infection. I'm sure more experienced folks will know. Good luck!
Or maybe lower grade sand than what's on the package? Hate to sound pessimistic, but according to my fish shop, aquariums and supplies are like the new toilet paper now, very high demand. After all, silica sand is the mother of glass - hope it wasn't sketchy labeling and/or that the little cory is treatable. I've never had sand for the cory cats, but hear it's best. I've always used the rounded river pebbles and have a happy little mob of them, at least for the last 5 years or so.yes, could be that if there are sharp rocks
another user told me something about how brand new sand causes some stuff like that?
No, it’s like fin rot. It is caused by stress and dirty substrate or anaerobic conditions so another could be affected by the environment. Do a large water change and vacuum your substrate well in main tank. Antibiotics are helpful in early stages. It’s kind of like an infected blister.Sorry I took so long. I left the test kit... somewhere. I’ll look for it. It’s CaribSea Supernaturals sand. 40 gallon tank. About a year old. I used a few root tabs when I first started the tank, but that’s it. I’ll dig out my old 20 gallon and set it up. If this is red blotch disease, is it contagious?