I have a gunnite inground pool. It's been running fine for 7 years then about 2 weeks ago, I noticed that there was about an unusual water loss overnight.
I re-filled the pool and tried it with the filtration off and on and the same. About 2 to 2.5 inches gone in a 24 hour period. I tested the evaporation effect by leaving the spa filled and it only looses about 1/2" in the same period.
There are no leaks in any of the pipes above ground.
I suspected the underground plumbing so I let the water go down to below the level of all the outlets thinking the water loss would stop. But it keeps dropping.
So I figure it's the main drain. My first question is - what does the main drain actually do? I don't know that it's actually connected to anything. One explanation I got was that it's just there to equalize pressure. I don't really undersand this.
Secondly, I'm thinking I'll have to go for a swim and cover the drain with some plastic and see if it stops the leak. Thoughts?