Turbidity Problem

Hi -
I have a 1 year old well that I'm having issues with. The well is 420 ft deep with a static water level of 100'. I have a Grundfos 10SQ15-330 pump that pumps water into a cistern, from where it's pressurized for the house by a Grundfos MQ. I have 2 issues:

First, the water has never cleared up since the well was drilled, having very fine grey silt (turbidity?) that will not settle out. I've had the water tested by a lab, and there's nothing outside 'normal' limits except the turbidity. I was able to clear the water by putting in a big-blue filter with a 0.35 micron element, but the element clogged up after about 1000 gallons. A 5 micron filter does not clear the water.

Second, the Grundfos SQ is supposed to have a built-in check valve, but it doesn't seem to work. When I turn the pump on it takes upwards of 20 seconds for the water to reach the cistern, and once it arrives is spit's and spurts for another 5 seconds or so. I assume this is due to air in the water line, which I assume the check valve should prevent.

My suspicion on the silt issue is that I may have set the pump too deep. I have 400 ft. of 1" PVC in the well, and the Pitless adapter is approx. 10' below the well cap. I'm not sure how much PVC stretches, but could it be possible the pump is too close to bottom?

I have no suspicions on the air in the waterline, or if the two issues are related.

I'd welcome any input or suggestions. Right now I think my options are to pull the pump, remove a section or two of pipe, and add a check valve.

Thanks.

Heavy sediment will settle to the bottom of the well, and raising the pump a couple of joints will usually help. However, light sediment or turbidity may be coming from anywhere in the well and is not heavy enough to settle to the bottom, so raising a couple of joints may not help a thing. If the turbidity does not even settle out in the cistern, it is very light.

You usually just have to pump the well hard for days or weeks to get it cleaned out properly. Adding a check valve may help, because water falling back down can stir up the well. Also when the pump starts with no water in it or pressure against it, it is pumping much higher volume than normal, which can also stir up sediment. The turbidity may also be what is causing your check valve to fail. If it has dirt in it, it can’t close properly.

I would try pumping out the well first. Once the well is clean, the check valve may work.

New well, silting problem, into 2nd week.

Have been reading forum sites looking for ideas. We have silting problems when well first starts. Location is Minnesota Lake Minnetonka area.
Typical cycle, 20 minutes on, 12 GPM, First 3 minutes clear, gets murky, and then clears up in last 10 minutes. If we wait for 20 minutes and start over, pretty much same thing, if we let run, then we get clear water indefinitely.
New well, 250 ft. casing, variable volume pump, 1.25 HP, flows about 25 gallons max. Static water level, about 75 ft., pump at 140 ft., 16 ft. slit screen PVC.
Well driller used air pressure to high flow well and start the development process, came back and did another shot for several hours.
Water quality is terrific, <0.25 ppm iron and we know if we go deeper, will encounter not as good water, i.e. WSIron, etc.
Question, Why are we having this issue and how long to keep bashing away on problem. Are there other cycles/steps that would yield better results.
Currently next step is to put a large spinning filter in line, probably go back to standard pump control to get max flow on tank recharge, Please suggest ideas. We are getting desperate to decide if we have to put in another well