Tom, Bill is right on target with his post. An area that also needs to be considered is that the "inert" part of a product like Princep or any herbicide can vary greatly. Most manufacturers use what is called "least cost formulation" for inert carriers or products with their AI (active ingredients) in this case simazine.As long as the inert part is tested and approved (labeled)for land use and field crops (Princep is a common product for fall panicum control in field corn)it is used. If the $$ market dictates a different inert later, than that is used. So you may be looking at a 90% simazine but the total package can vary by manufacturer and vary by batch number from the same manufacturer. This is one of the reasons NOT to use a product in your pond that is not labeled to do so.With products like Simazine being off patent many manufacturers compete for the market from around the world. You have no way of telling what makes up the inert. When these materials are applied according to the label they will breakdown over time and degrade often 1-2 years The same products in water can persist for much longer.Simazine is also a great pre emergent grass control product. Any new lawn trying to get established and irrigated with a Princep treated pond will show the impact from application made in prior years, Ted