Fish Zole is the same as Aqua Zole the newer brand name. It is the same as metronidazole, and not the same as Nystatin or Medistatin which treat fungus or yeast.
Look for miconazole or clotrimazole creams in your pharmacy. They may have brand names, but those are used for men’s and women’s fungal infections. Your vet’s office may be able to tell you if there is another brand name for Nystatin or Medistatin. Continue to smell for a bad odor, and then...
Then it could be fungus (thrush, candida, yeast.) If it develops a bad odor over the next few days, still consider that as canker. For fungus, Nystatin is good. It is a prescription drug from a vet, but you can get the powder form here online called Medistatin and dosage for oral administration...