My pool has a touch of black algae behind the light. My local shop sold me a "Black Algae Killer" to take care of the algae. It has Copper as elemental, C14,C12,C16 and dimesthul benzyl ammonium chloride. On the label it clearly warns, "Corrosive. Causes irreversible eye damage and skin burns." I don’t understand how this can be safe to use. If i put it in my pool and swim with it I’m still being exposed to it.
Actually, like many chemicals that are potentially harmful, it changes form when it is put into the water and it is greatly diluted as you are using such a small dosage compared to the size of swimming pool. This is the reason why these types of products do recommend that you wait some period of time before re-entering the pool as you do want to make sure the the chemical is not dangerous. A copper based algaecide is widely considered to be the best remedy to destroy the black algae. Other algaecides do not even treat this stubborn algae.