I have one of those preformed ponds, not too big, only about 125 gallons, and it does have some age on it. This year it appeared to be leaking. A puddle forms beside the pond and the water level is down a few inches. First time it happened we quickly refilled the pond until we could make other arrangements for the fish/plants but in the meantime the water level stayed up. Hmmm, we thought maybe we were imagining a leak and that first drop was just evaporation from all the heat. However, it has happened two more times. We had storms Sunday evening and yesterday the pond was filled to the brim from all the rain. This morning it is down 5". No evidence of raccoons or anything other mischief causing critters. It has to be a leak but why is it only sometimes? It stays full for weeks then abruptly drops. It is driving me crazy.
Maybe the leak is higher up and when the water drops below it....no more leak. The rain filled it again beyond the leak and it dropped to below it. Could that be it?
I had the same problem! I had a small pump in the bottom, and if I left the bottom gunk settled, it seemed to be ok....but if I moved the gunk at all, it would drain over night. The pump seemed to keep the water going uphill and not allow it to drain as quickly, but if something was a-muck (almost a pun there) it would drain.
I finally bought 2 tubbies, one for plants, one for fish, and quickly drainied it, used waterprrof caulking, inside and out, and refilled it. Seems to be ok now. I had to use a flashlight at night to see where the little hairline cracks were!
I have the tubs ready. Maybe it is time to drain the pond and see what's up. Interesting about the flashlight at night.
The strange thing is it stays filled for weeks then drops suddenly. It must be "muck related" like Mary says. :-)
Thanks Rosie's mom and Mary.
Be sure to let us know when you solve the mystery!