I can't confirm that your photos depict Chara. I'm thinking it might be Nitella (they're "cousins" in the higher order of algae).
But, in either case, I agree that CUTRINE GRANULAR is preferable for targeting suspended and bottom-growths.
Not sure, but it now sounds like we're talking about canal with a public water-body. If so, it is advisable to consult with the lake's governing water authority (a river authority?) before conducting any private treatments. Unlike other scenarios, it is best to secure permission rather than seek forgiveness when dealing with public water treatments.
