Pany leaf spot is very comon on viola and pansies. It is spread more by over water over the top as spores spread very fast. Spraying with a chemical which you can by at any local garden centres (Diathane 945) it should be sprayed a the first sign of infections. The chemical protects the new grow as it produces a film to prevent the spores from germinating. Try that and let me no if it is working ...