Bing, Aquashade is registered with the EPA for weed & algae prevention, but it has a label warning to not apply to water that is to be used for human consumption. Below is a link to the manufacturers web site:
http://www.appliedbiochemists.com/ (Now owned by SeaPro)
I'd email your question to them.
Aquashade, and other pond dyes, will prevent submerged algae from growing, but it will do nothing for mats of algae on the surface or duckweed. Also, you have to consider other effects of the pond dye. It will prevent beneficial submerged aquatic vegetation from growing, which can inhibit the ponds capacity to process nutrients, which can lead to more algae. Pond dye can also disrupt the food chain, which is a problem if you are managing for quality fishing.
I'd look at other alternatives in your situation, like aeration, encouraging beneficial native aquatic vegetation, and spot cutrine plus treatments, if necessary.
