Question
I have a fish pond (large) in clay soil, that is impermeable, but has weed (aquatic growth) problem. Too much weed growth from bottom. I have found Preen Landscape Fabric, that says it prevents weed growth in gardens. Can I drain pond, apply Preen, and re-fill. Will Preen harm fish??

Answer
Hello,
Thanx for your question.  I believe Preen may be harmful to the fish.  By aquatic growth I am going to assume you are talking about string (green) algae growing from the sides?  Use a few floaters such as water hyacinth, water lettuce, azolla which are water plants that float on the top of the water.  Their root systems strain the water and help filter and keep it clean.  Also, barley bales (available at nurseries that sell water gardening supplies) help keep down green algal growth.  I hope this helps.
Tom