I would think that any IG pool that has a chance of ground water being higher than pool water will have a hydrostatic valve. This is what keeps the pool from becoming a boat and rising out of the ground if the ground water gets higher than the water in the pool. You might go to a pool store and get a look at one so you can see that it is a spring loaded one way valve that should let water in but not out. Mine is part of the main drain box. Good luck, PaulOriginally Posted by xoroniox
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