Sand Filter Getting Air

Air getting in the filter can only mean one thing - leak on suction side of pump, air leak anywhere else and it'll be water getting pushed out the leak.
if it's not the strainer basket or low water level, have you chacked all connections between the skimmer and the pump - this is the ONLY place you could be drawing air from.
in answer to your recirculate question - nothing should change since you are effectively bypassing the filter and just pumping water from the pool through the pump and valve of filter (valve only) back into the pool.
Have you got a bypass chlorinator on the system - these usually connect into teh main lines before the pump and after the filter, the air could be getting in before the pump - check the stainless clamp to see if it's tight enough.

I do not have a chlorinator but I will put the pool on bypass and run it. I will watch the pressure gauge and for leaks and post what I find. Thanks.

I just put it on by pass to pool. The pressure went down to 8 and the flow of water coming from in front of the jet was the strongest I have ever felt. I didn't see any leaks though. What does this mean?

Very good, it means we are eliminating some things.

Air leak not a problem. Pump is in good shape. Skimmer and lint baskets are clean.

The sand is apparently restricting the flow of water. I would try a good long backflushing and if that does not help try changing the sand.

Any other ideas?

I just replaced the sand last year but had a problem with an older pump. I had to backflush alot could I have channeled the sand?

I looked back through this thread a couple of times and don't see that anyone has talked about backwashing at all. Have you done that? You mentioned that the filter pressure is about 20 PSI, is that normal for your system?

If you channeled the sand you'd have a low backpressure and bad filtering but not air.
Since you had no leaks testing, you could still have a small suction side leak before the pump - it could be really small and would only ever draw air when the system is on, it may never draw a huge amount of air due to it's size.
If you turn the pump off, and let it sit overnight, you may find a small wet spot somewhere between the skimmer and the pump - you would have to trace that back to the leak uphill of it.
The only way water will come out of a suction side leak is with the system shut off.

I have pvc piped my pool last year to prevent leaks. I have went over every joint with pvc glue to make sure I didn't miss something. I do have a piece of heavy blue hose from the pump to the filter. I made sure that I used pipe threading compound on all to prevent leaks. When I backwash my pressure runs 20 psi. This is the usual pressure for my pool on filter also.

A freshly backflushed filter should pump about the same amount of water as the by-pass mode. It sounds like you are no where close to this.

Do you remember what type of filter media you used last year? I'm still thinking that is your problem.

#20 silica sand from the pool store. How long are you suppose to backwash for. I usually backwash until I can't see any particles flying out the backwash pipe.