You can also try a quart of PolyQuat. It's not exactly a floc, more of a clarifier, but it's also the ONLY algaecide we recommend besides chlorine.

You'll find it under the names Algaecide, Black Algaecide, Mustard Algae Treatment, etc.

However, it's ONLY ingredient is 60% Poly...<something, somthing>... If it's got only that, it's PolyQuat. Usually you use less, but if you need to clarify it...it works great.

One GIANT caveat: Within 48 hours of adding the Polyquat your FC will drop to near-zero. Don't panic. Just add more bleach/Liquid Chlorine to bring FC back to your desired level. If FC accidentally drops again, the Polyquat should keep algae from immediately starting to grow, as least for several days.