Submersible system mystery

[Adkroot]

I've had an ongoing issue with my water system that I could use some input on...

I have a low flow 24v dc submersible set at 40' below static water level (max allowable depth is 50') Well depth is 160' in bedrock.

Drop pipe is 1/2" (required) and from the pitless to my tank I have 3/4" k copper.

Static water level is 43' from pitless and lowers by a foot during demand. 6" diameter well.
Pressure tank elevation is 2' higher than pitless and pressure switch is 40/60. Bladder pressure is 3 psi lower than cut-in.

The pump at current head will deliver 1.7 gpm, but for a few months now, once we've depleted the pressure tank's storage and are drawing directly from the pump, the flow drops off significantly. After the tank has filled and water is drawn there's some air blasts and the water is cloudy with air bubbles. This got worse over time to the point where the air blasts were large. There's more air in the hot water than cold, but both increased.
Static water level was unchanged and the pitless and drop pipe connection were not leaking.
I pulled the drop pipe from the pitless and the pipe was full with water so I assumed the internal check valve was functioning. I installed a check valve just downstream of the tank manifold and a pressure gauge downstream of that to verify if there was a leak in my buried line. The gauge at the manifold and the downstream gauge climbed evenly to the shutoff pressure, and after shut off the manifold gauge held at 60 while the downstream gauge dropped to zero. This signified a leak to me and explained the lower flow and air. A couple months passed (this was going on during dead of winter). When I rechecked the pressure switch it had corroded some and cut-in and off was now 50/74.
Before I dug a 70' trench for a new line I decided to recheck everything. I installed a new switch and new gauges and all of that functioned normally and the air blasts were mostly gone, though the water is still cloudy with bubbles. I pulled the drop pipe from the pitless and checked the flow direct from the pump. It was as low as we were getting in the house when running direct, so I considered that maybe there was no leak. I pulled the pump to recheck all connections and they were all sound. The drop pipe was also full of water. I installed the pump in the well and energized the system. The downstream gauge is now holding pressure at shutoff, but there is still air bubbles in the water.
My conclusion is that the pump seals/diaphram/check valve need to be replaced, but why the air in the system?

 

[Reach4]

It could be the water level got pumped down. You could fill an atmospheric storage tank at a rate that the well can keep up with. Then use a pressure pump to provide pressure to the house.

Static water level is 43' from pitless and lowers by a foot during demand.

That would say you are not running out of water. So the question would be this: how sure are you that the water does not drop way down? If you are able to actually monitor the level during the problem times, then the running low on water idea could be discarded.

 

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[Adkroot]

During demand the static water level only drops 1'. I'm certain of this having sounded the well during peak use and off use. Also, this pump won't run unless submerged. The pump isn't delvering the gpm it should be and that could be an issue with the diaphram, pistons, or the motor itself. The cloudy with air bubbles water and recent bursts of air are perplexing.

 

[Reach4]

I installed a check valve just downstream of the tank manifold and a pressure gauge downstream of that to verify if there was a leak in my buried line. The gauge at the manifold and the downstream gauge climbed evenly to the shutoff pressure, and after shut off the manifold gauge held at 60 while the downstream gauge dropped to zero. This signified a leak to me and explained the lower flow and air.

Your diagnosis seems correct. While the air is being sucked in, contamination could get sucked in if the leak is underground vs in the casing.

A leak in the pump or below water level is not going to admit air.

The above-water leak could be at the pitless o-ring. Or elsewhere. If you removed the innards of your above ground check valve, you could listen or watch for water at your un-capped casing. It sounds as if you already made that check.