Your world must be very small. The only references I found about excel
being an algicide (algaecide) on google were posts you made. Nothing else.
No research by seachem anywhere indicating this is an algaecide. There is
no government regulation preventing seachem from calling an algicide and
algicide. There are regulations though that prevent companies from making
false claims.

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Margolis
http://web.archive.org/web/200302152...qs/AGQ2FAQ.htm
http://www.unrealtower.org/faq