Aquatic pond dyes are often very useful in helping limit or reduce pond algae growth as well as underwater weed development. The dyes that we carry are blue, black, or blue/black in color and non-toxic to fish and other aquatic wildlife. Whether in liquid or powder form, the intent of the dye is to limit sunlight penetration into the pond and thereby retard the process of photosynthesis. This is the natural stimulation that often helps algae and weeds grow in a pond.
We recommend using the suggested amount on the package or less, based on your pond size. The goal is to create (in our opinion) a light tint that, while it's pleasing to the eye and allows you to see into the pond somewhat, it will help cut down on the light penetration. You may need to experiment with the dosage to achieve the desired results.
Many people continue to like and enjoy the standard blue coloration, however in recent years, black dye has been gaining in popularity, as has the combination of blue and black colors. By adding a bit of black to the mixture, many people (us included) believe that these provide a more natural appearance compared to using blue alone.
The duration of many dye products is often a month or more long, however this can be affected by water turnover in your pond to some extent. For most ponds the dyes will last for a number of weeks.
We don't view pond dye as a full preventative for unwanted plant growth. Sometimes it is, however it usually works best in combination with beneficial bacteria or other treatments. It is particularly helpful in shallow ponds of 6 feet or less.