I've been wondering if the several inches of ice this winter have caused a leak in my small pond. It's definitely going down, but I can't do much about it now till the autumn so I'm filling pails of water to let them settle for two weeks so I can top it up. I suspect the hole is very small & probably won't be visible to the naked eye, so we may end up biting the bullet and replacing the whole liner - an opportunity to make it a tiny bit bigger .....
Re the tadpoles - they will survive in quite shallow water so if you can keep it topped up a bit between rain showers, they may get through until they grow legs? hard to say without knowing how big and how much water?