I have a pregnant stingray in a 340 gallon tank along with about six angels and twleve discus. Unfortunately I have been losing about one discus a week due to illness. Each week a discus gets uninterested in food and wastes away 'til death. I feel awful. I purchased "Dewormer", "Metronidazole" and Prazilpro but don't want to hurt the mom stingray or the pups.... What do I do? Suggestions fish MDs?