Barley straw cleans ponds and it’s safe for fish.It’s also safe for livestock. We use barley straw bags in our horse tanks. As long as you change them regularly (see the label on yours for info), they work great!
This advice is intended for anyone installing a small (under 1000 gallons - about the size of hot tub or less) prefab garden pond or other little container pond on a patio or balcony. Ive had several different types of ponds over the years, and,