I thought that they claim vibrant contains a community of microbes (as in products like microbacter 7). If so, it probably is to think that even with a few microbes you could hit the majority of common algae.I agree that there are algae eating microbes but a completely indiscriminate form that eats any algae it comes across seems unlikely to me. The biology of different algaes seems too diverse for that.
After all, the bacteria don't need to eat the algae, they can simply eat a molecular component of the algae (e.g a commonly used cell wall glycoprotein or polysaccharide).