1) Kelp poison 
killer of algae
<pharmacology> Any chemical that kills algae. ... (09 Oct 1997) ... 
(al´jĭ-sīd) destructive to algae. an agent that destroys algae.
A chemical used to control algae, often referred to as aquatic weeds.
Type: Term Pronunciation: al′ji-sīd Definitions: 1. An agent active against algae.
algaecide, algicide The killing of algae; a preparation used for destroying algae.algicide Any substance that kills algae.
Substance or chemical used specifically to kill or control algae. 
a substance or preparation for killing algae.