Sorry I didn't post more info. I wasn't sure when I gave the info at signup where it was going to go.

What are the ingredients of the powdered shock?
Trichloro-S-Triazinetrione and inactive ingredients

What is the size of the pool?
4,400 gallons (4 x 15 ft.)

What is the source of your fill water --- a well or city water?
city water

How long ago was it filled? Why did it turn green if it was just refilled?
Last winter, when it got too cold to use the pool, my mom apparently just left it there, filled, uncovered, and probably untreated. Then, she died unexpectedly in January. Nobody really knew what to do to take care of the pool, and there wasn't much incentive to since it was too cold to swim.

A few weeks ago, my sister came by and emptied the pool, thinking she was going to take it to her house. But a relative offered to buy her a new pool instead. So, we refilled the pool.

By the way, according to the test strips, the pH is now correct.