Welcome, Joel! I am only a year into owning a pre-loved pool, so will chime in with my limited experience. I am sure one of the forum wise ones will be along to help, too! They are very generous with their time and knowledge.

The pump in the middle is for your spa jets, I would bet. That dome shaped thing on top with the switch hidden by the electrical outlet cover thing, on our pool setup, is basically a booster for the spa jets to increase the pressure and give you a harder massage. I think it's called a spa blower, and I have googled a picture for you which I will attach. Ours sounds much like a shop vac when we turn in on, so we don't use it really. It makes sense that's the spa setup since it's closest to the heater, too.

We have three pumps but no waterfall features, but I would think it makes sense that they have their own pump because there would be times you don't want them on. The way our pumps are setup is:
1. Pool Circulation (with its own sand filter)
2. Spa Circulation (with a smaller sand filter and a heater)
3. Spa Jets / with Booster Blower

Perhaps your spa circulation and your spa jets are one in the same. It looks like there is a smaller filter with it. The one on the far right in the corner is your pool pump, since it has the big filter attached to it. That leaves the one on the left as your waterfall feature.

You may try turning them on and off individually to see what happens when you try each.

Our pumps are all single speed and nothing fancy, but we wanted to reduce our energy use so we had a timer installed on our pool pump. It is the lion's share of usage, so the timer really helps. We have tiered usage electric rates in the summer (when the pump is needed) so I had it set to run only overnight when the rates were lowest.

Here is a link that might be useful: pic of blower

This post was edited by MiaOKC on Wed, Feb 20, 13 at 10:32