I had anchor worms and lice in my fancies pond and single tail ponds with common water, I caught it early but searched for something to treat the pond with for a few days until I found an aquarium store who referred me to his source for Express IDI and they shipped it to me next day. By then the infestation had gotten worse, from 1 fish to 10 fish I could see. I treated at the recommended rate of 1/2 teaspoon per 1000 gallons and by the second day I could tell the anchor worms were dying and by the fourth day there were no signs of the anchor worms or lice. It states no water change is required and one treatment is usually all that is required but I am going to make a second treatment just for safety’s sake. I’m relieved I found this product. It worked amazingly well for me and my fish.!