Thanks for all of the info. The pool is looking MUCH better. I can actually see the bottom now. The previous owners left 2 extra cartridge filters. I cleaned them off and replaced the one that had been there all winter.

Now that the water is clearer, I can see LOTS of debris in the pool. Leaves have collected in a couple of places and the dead algae is at the bottom of the pool. I saw on another thread where you had recommended a leaf rake. I'll be getting one of those real soon.

In the mean time, I was trying to vacuum the algae from the bottom, and am having trouble with getting air in the system. Once I changed the filter, I had very good circulation, but now it just seems like a slow trickle.

Is the replacement filter clogged? Is it air? And if it's air, how do I get it out? I'm still now entirely sure how the valves work. I've got a valve before the pump and a valve after what I believe is called the chlorinator. Both of those are in the up position.

Again, thanks for the help

Greg