Using water tints, aquatic colorants or pond dyes can help reduce algae growth and weed growth by filtering out sunlight from the bottom of the pond. Dyes are non-toxic and safe when used as directed. Beyond the potential for aquatic weed prevention dyes can also beutify any sluggish or brown pond quickly turning it into a more paletable shade of blue. Black dyes create wonderful dark flective surfaces and there are even red and green pond dyes that add whimsey as well as filter out the sun. Used in small water gardens, earth ponds and small lakes around the UK.