Water Colorant Helps Control Algae by Filtering Out Sunlight for Plant Photosynthesis

Using blue dye to colour water and discourage plant growth is not something new. Golf courses have been using it for years and now fishpond owners are starting to use it. Plants need light for produce photosynthesis and growth but not just any light. Light in the red and blue wavelengths are critical for growth. Application of blue dye does not reduce the light available to the plants. Instead, it acts similar to a blue filter on a camera, restricting all the blue light entering the camera. With this dye in the water, light enters all the way to the bottom but the blue light is absorbed and not available to the plant. This results in submerged water plants being unable to properly photosynthesize and grow.

The same is true for the mats of algae that first begin to grow on the pond’s bottom and then suddenly surface in the warm summer’s heat. With the dye in the water, they cannot grow and the bottom of your pond remains bare and algae free. Shoreline plants like cattails are not affected because they are rooted and have leaves above the water to catch sunlight.

“Application of blue dye is very easy,” says Grekul. “We first used dissolvable plastic bags, so all you had to do was throw the dye bag on the water and watch the colour disperse. This year we used a liquid concentrate but I think I like the bags better”.



Cost of treating a normal dugout is about $125 and the treatment can last all season. The blue dye is harmless to fish and animals and completely safe. “Now when we pick up our fish we pick up our dye and we are set for the season,” say Grekul.

Pond colorants are available in Alberta under a variety of names.

This article was contributed by Doug Millar, a former commercial trout farmer and director of the Alberta Aquaculture Association.