I recently moved into a new house that has a perimeter overflow pool that is being maintained by a pool company. We have been having constant problems with water clarity and algae and the maintenance guy has told me it is because the pumps are only drawing water from the surge tank and that is causing problems with the water circulation so he has opened the valve from the main drain 50% and the valve from the surge tank 50% and said this will resolve the issue. The only problem is by doing this it greatly reduces the amount of water passing over the edge. I have spoken to a few people that have said that the main drain on an overflow pool is only used for emptying the pool and the valve should stay closed when under normal operation. Any advise would be greatly appreciated.