Thank you all for the very warm welcome. It is much appreciated. I'll try to answer as many questions as I can.
The "plankton" like debris that I was seeing in the water was more than likely, DE residual from my old filter. The grids in my old filter were cracked and letting the powder into the pool/spa. I tried vacuuming the DE off the bottom but it just went through the filter and back into the pool. After I installed my new filter, I vacuumed all of the DE from the pool/spa, then brushed the pool surface. Brushing turned the pool pretty cloudy but I thought the filter would clear things up. The pool got as clear as it was going to get 8 days later. I think my continuous brushing may have contributed to the water not looking as clear as it used to be. I haven't brushed the pool in 3 days, now, and it looks much better, but, not like it used to.
The flow into and out of the filter doesn't appear to have changed but my old filter didn't have a gauge, so it's hard to tell. The return fittings in the pool feel about the same as they did? I always felt they were a bit weak, anyway.
The 3 inlet valves are as follows:
Main drain, closed.
Wall vacuum, open.
Skimmer, part way open. (I adjust the skimmer valve to set the proper suction for my Navigator) If all three were open, or even two, I would not have enough suction for the Navigator.
As a test, I will open all three valves and check the pressure again.
To my knowledge, the motor is 1.5 HP The pool has 4 returns. 2 in the pool, 2 in the spa.
The reason there is DE on the pad is because after the installation of the new filter, there was a tiny water leak at he high side of the pump, at the pump. The only way to repair it was to cut open the PVC to the filter (you can see the repair collar in the photos) and reseal the threads at the pump. While the PVC was cut, I opened the air bleed valve and water, and a whole lot of DE was spent from the open pipe. I add DE very slowly, through the skimmer.
Oh, BTW, the gauge is reading a steady 6 lbs, not 8 or 9 like I had thought. I keep hearing that 18-20 would be normal.