I am helping a friend with her lovely forest green water and a cya of 100. We are drawing down the water in an attempt to get the cya in a better range (30). The pool is ~20 x 36 oval inground plaster with a spa. The skimmer has 2 holes in the bottom. One is definately sucking. Where does the other go? to the main drain? What I've noticed is that the spa emptied quick and the first 3-4 inches went quick and then the skimmer stopped sucking because it was below the water level and consequently the suction slowed down.
What I don't know is how the pool is plumbed.