Pool leak, water rises-pump on,lowers-pump off

[mollygirl]

Heres a good one for you all, welcome any sugesstions. Opened the pool 1 week ago. Ran the filter continusously.Every morning the water level rose 2-3 inches (no rain).I would backwash to bring it down, yet it kept rising. So I turned off the pump for a night and the level dropped slightly. Ran it for the day, rose again. Turned off pump for the night again, this time it dropped about 3-4 inches. Now every time I turn the pump off,it drops significantly. I plugged up the stairs, shallow end, deep end and skimmer one at a time to see if the problem continued and it did. I assume it is the main drain. I thought maybe there was a crack in the main drain piping and sucking in in water from the ground and blowing it back in and when the pump is off it leaks out. But if I have a crack in the main drain piping, why did'nt it drain over the winter?? PLEASE HELP!!!

[sameproblem]

I have a similar situation. I have been told that a valve that is supposed to close when the pump is turned off does not shut so water flows backward. I am not actually loosing water since I do not need to add any when the pump goes back on. You might have someone check your valves.