rain forest blue?

Copper sulfate! My advice is to stay away from it! NOT an EPA aprroved sanitizer on its own! The instructions for it do say that you still have to shock (add chlorine) to your pool! They just don't tell you how often. Copper is an effective algaecide and if you keep your copper levels in the .6 to 1 ppm range they recommend then you will not have any algae but it doesn't mean your pool is sanitized. FYI, most copper based algaecides are dosed to abut .3 ppm unless you are dealing with a very green pool or black or mustard algae, in which case they are dosed to .6 ppm. High copper levels can lead to staining of pool surfaces and can cause green hair!
Kill times for copper are very slow when compared to chlorine, bromine or biguanide sanitizers. In a pool or hot tub fast kill times for pathogens are important!