Is Acetanilide toxic to fish? I understand that acetanilide can hydrolyze to aniline and assume that will happen if that gets added to an aquarium, thus causing toxicity?

I have a solution that is $3\%$ hydrogen peroxide and $0.25\%$ acetanilide that I'd like to add to my fish and shrim aquarium to kill some algae.
When I checked the SDS of acetanilide on Sigma-Aldrich website, I saw that it is harmful to aquatic life. 
So, there is no exception whether it is an alga or fish to kill. I suggest you not use acetanilide in the aquarium.