[Reeses]

Where exactly would they put the million of acres of ponds needed to grow enough algae to make a dent.

This pond is big enough. It has free water, free farm fields, and free sunshine. It also has free fertilizer waste feeding into it. Algae blooms aren't a problem because of too much algae, but because of not harvesting it.

[BitWielder1]

This pond is big enough.

You can't put algae in the OCEAN! Are you crazy?
Algae farms pollutes and destroys sensitive ecosystems, don'tcha know?
You can't harvest the existing algae either, think if the ecosystems, fish, pollution, rare species, coral reefs, pH balance etc. and yada yada.