There are 3 main factors that work together to have a great looking pool. One is chemical balance, the second is clean filters, and the third is good circulation. Having only 2 of the 3 taken care of can make a big difference in how your pool looks. The following 2 pictures illustrate one example.
In this case, a client had a motor burn out and needed to purchase a new one. Her filter was only about 2 months old, and the pools chemicals were in perfect balance. It took about 9 days before deciding on a motor and how much to spend and getting it scheduled.
That week was also very windy, and the 2nd picture is how the pool looked before I cleaned it after the motor was running again. There wasn't any algae, but the amount of dirt/debris just sitting on the bottom is significant in that amount of time. Not all pools would be this bad, of course, after 9 days, but it's a good portrayal of how a relatively short period of no circulation may affect your pool.
If this happens in the heart of the summer, however, you can guarantee there will be algae formed and it may be a whole lot worse. Check out our algae removal page for a picture of what it may look like after sitting with no circulation for only a few days in the summer.