I have used Food Grade Diatomaceous Earth (DE) in my pets' food for about 4 years for internal parasites. I also use 1/4 to 1/2 teaspoon 'organic' apple cider vinegar (ACV) per quart of drinking water all year. NO fleas or tics, the ACV causes sour blood... fleas/ticks don't like sour blood!! I like this better than putting DE on their fur. My one cat had severe fur loss on her hind end and weird pumps all over her skin, I 'think' the fleas caused this. Since using ACV in my pets water, her fur is thick. I also give Krill Oil in their food.