I have been losing cories at an alarming rate. I put in about 6 pandas 2 and a half weeks ago and I now only have 2. I think that the second store I got them from had them infested with an internal parasite as they have been wasting away. I tried first levamisole about a week ago and I still had loses so I bought focus and metroplex and made some food to give the tanks. One cory went from fine and died overnight with no warning. As advised, I changed from gravel to sand and I am currently going through a mini cycle. And I have dosed with prime preemptively to handle any ammonia. Does anyone have any thoughts?