Unfortunately there are many many factors that cause tear stains. Everything from minerals in water, excessive tearing, genetics, health, diet, fleas, allergies, blocked tear ducts and the list goes on. Most people can try to get a professional opinion from their vet or try different things to rule out. A premium food with no fillers, corn, dyes including treats is an option. Most recently I have seen great results with Angel Eyes, a supplement used with food. Two maltese I groomed had the worst stains and after this product, no more stains with their next visit. The other product is Eye Envy, the only downfall is applying a solution then apply a paste two or three times a day which most owners do really well for the first week and then cut back over due to busy schedules. Through the years, groomers have tried many over the counter topical eye stain removers with little to no results. On the Angel Eyes Website, there are over 23 pages of success stories. You can get this product at most pet stores but keep in mind it may work for some not for others.
Always check with your vet before using Angel Eyes due to an antibiotic in the ingredients. Prolong use of antibiotics could cause a resistance to antibiotics in need of a medical issue.
A newer non-antibiotic eye stain remover formula is called Tear Stain Supplement by Vet Classics. It’s also a powder supplement given as needed or until stains are gone. I found this widely on the web on different sites as well as Ebay and was referred this product by one of my clients given to them by their vet with good results. Another similar product can be found at PetFoodExpress called Naturvet Tear Stain which has mix reviews working for some and not for others.