Algaecide caused my pool to foam a couple of weeks ago, too. Mine is smaller (only 7600 gallons) and I spent hours trying to scoop out the foam. I finally gave up and within a couple of days of adding bleach to get the high Cl reading, the foam was gone.

For a while, though, I was really afraid that I was going to look out the window and see the pool overflowing with foam!