The Truth About Pond Dye Pond Dye...The Truth Does Pond Dye Really Inhibit Weed and Algae Growth?Much has been claimed or written by various manufacturers of pond dyes and pond colorants stating that their products control, inhibit or suppress weed and algae growth in lakes and ponds. While some companies have sought EPA registration for aquatic weed/algae control others have not seen the need for it. Either method can be the right choice, depending on several factors. Companies get into trouble when they accidentally or intentionally confuse the difference between making these claims with proper EPA registration or going without while still making “kill claims”.What do all of these pond dyes have in common? The vast majority of pond dyes and pond colorants are made primarily from blue dyes (such as acid blue #9 or similar) and some companies blend a smaller amount of yellow dye, resulting in a more greenish tint to the water. Those products with EPA registration supporting claims of algae/aquatic weed suppression or control will state that blue or blue/green dyes shade the aquatic plants from available sunlight thereby inhibiting their growth (or some description similar to this). What the consumer should keep in mind is; several states restrict the use of EPA registered products. Crystal Blue Lake & Pond colorant is NOT RESTRICTED. Crystal Blue pond dye can be used in any state.Crystal Blue Lake & Pond colorant does not make any claims either on our labeling or our website, stating or implying that Crystal Blue makes such claims. Some manufacturers are much less clear. If killing algae or aquatic weeds is your desire, then we would suggest you combine the use of our Crystal Blue pond dyes and pond colorants with our own EPA registered products like Crystal Plex Algae Control, Tsunami DQ for aquatic weeds or Catt Plex for cattail control. These products are all properly registered and safe when used as directed.