There is a device by the pump where i can manipulate where the suction occurs. When I turn the dial to have the suction from the skimmer, water flows into the pump. When I turn the dial to suck from the main drain, not much water runs into the pump. Just to note most of the time a i have the suction sharing between skimmer and main drain. Due to water loss, water is starting to go under skimmer, so I decided to pull water from Main drain and saw no suction into the pump.
 
I gotcha' now. Most surely, that is a valve (often called jandy valve) that performs exactly the purpose you are describing....that is it's only job.

It sounds like your main drain is either inadvertently plugged by debris or plugged on purpose by a previous owner. Both situations are common.

If it is debris, some have had good success by getting compressed air blown into that main drain line and pushing the debris backwards back into the pool.
 
have you done a bucket test yet? i just had a very similar leak. i was losing 3/4" per day and the inside of the bucket was only losing about 1/4". my leak ended up being where the mouth of the skimmer meets up with the waterline tile. look there and around the light niches with food coloring to see if water is being drawn in.
 
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