Answer:

The green slime is probably suspended or floating algae that has collected in the skimmer. This would mean that the algae likely started somewhere else in the pool and made its way to the skimmer. Check for sufficient chlorine levels as well as proper circulation to make sure there are not areas of stagnant water due to the direction of the return jets. Once the water is properly balanced, you may need to add an algaecide dosage to help the chlorine prevent future algae growth.