I recently installed my pond with a firestone liner. Everything was fine...no leaks or anything. I used some driftwood (large piece) to cover up my filter and it was partially submerged in the water. I started noticing my water level going down some each day. I checked my waterfall and couldn't find anywhere it would leak. So.....I really didn't think it would fix the problem, but I was willing to try anything....I moved the piece of driftwood so that it was completely out of the water. It has been 4 days and the water level hasn't gone down any
I guess it was soaking water up and then it evaporated....pretty crazy 
