I have a 2500 gallon pond, cement with liner, and woke up the other morning
to find that half the water was gone! I found a small hairline crack along
the smaller waterfall - perhaps a foot long. The water flows over the
crack; the crack is not submerged. I patched it and everything seems fine.
Does this make sense that this was the problem? 1200 gallons down in 12
hours? It was raining hard that night so I could not tell if it was wet in
one area or another. I had this problem before but I would lose maybe 2
inches a day, not a foot and a half of water in a night.

Also, now that I am paranoid, I had this idea for how to stop the pump if
the water drops. I have a 1/5" intake tube that goes to the bottom of the
pond. If I put a T coupling on it a couple of feet from the bottom, if the
pond ever dropped lower than that would I not lose prime and suction -
hence, causing the pump to stop pumping the pond dry?

Gary