So I have a plastic pond liner pond which is about 4 feet wide and 2 feet deep. Recently it has been losing water all of a sudden. We had it for around 10 years and it started happening all of a sudden. And right next to it is an even smaller circular shaped pond which gives the water fall to the bigger pond. We use a 80 gph pump and connect a tube so the water comes out from there. We have 4 small comets in there and recently I put in a water lettuce. Its after a couple weeks after I put in the water lettuce the pond started losing water. Every couple days it loses like 2 inches of water so I keep having to add more water in it. What could be the cause? The pond is in shade all day and gets absolutely no sun btw.