By my calculations it would take an area of ocean roughly twice the size of the Great Lakes to make enough to cover U.S. Consumption.
Yes, and all of the people of the world would comfortably fit into a building 2 miles by 2 miles by 2 miles. (Providing you didn't need any infrastructure to access them)
You not only need to get the S#!t into the bags, you have to get the algae out. Then you need to replace the bags, fix the failures, and remove the failures. You need a WHOLE lot more than bag space to do this.