Copper(II) sulfate
Copper(II) sulfate, as the most common copper compound, has many uses. It can be used to kill algae and fungi. Some fungi can get resistant to copper sulfate, though. Then the copper sulfate does not kill them any more. It can be mixed with lime to make a similar fungi killer. It can be used to treat aquarium fish for infections. It is also used to detect sugars. It turns into red copper(I) oxide when reduced by a sugar. It can be used in organic chemistry as a catalyst and oxidizing agent. It is used to see whether blood is anemic.