Leak in liner? Losing water, Help!!

Hi everyone! This is my first log in this summer, computer has been wacky! We are having big problems. We are losing 1-2 inches of water a day. We are below the skimmer, so that eliminates that problem.We have a 20x40 inground 19 year old pool. I know liners don't last forever, but... We don't have the resources to replace it. I am so sad, our 9 grandchildren are all swimmers now, and love the pool. HOW do you ever find the source of leakage?? One question, we have had the pool light fixture open for years without the glass cover on it, I don't even know where it is. Usually they say they are areas for leakage. Is that asking for problems being open with water in it all these years? HELP! I am so hoping we can fix it and get a few more years out of it. On the plus side, I owe so much to this forum. You helped me convert to chlorine 3 years ago. It was the best move ever. Our pool is crystal clear, never cloudy, and I love the fact I am in control of testing it and controling its outcome. I tell everyone about the forum, and taking control. THANKS!!!:)

Water appears to have stopped descending today. It is below the skimmer. The other different thing we did was plug the return down in the deep end. Could water have been seeping out of that?? HELP!? Any help would be appreciated,thanks!