I'm not sure about the gauge working correctly although I just bought it new and installed it.

Yes the water does run dirty for four or five minutes when back washing.

I do not know if the filter has enough sand although the previous homeowner claims that it does but considering the source... I DON"T KNOW.

I have not tried turning off the pump.

Yes, until I got the CYA built up it would drop to almost zero after a day in the sun.

Thanks