Check the plumbing from the pump to the waterfall or other return for leaks.
Check the waterfall for water being diverted from the stream to the ground
around the pond. If the waterfall has plants in it, look at the spillway to
be sure the plants have not blocked the route of water flow back to the
pond, causing water to go over a different side. The most frequent causes
of water loss are associated with the waterfall.
--
RichToyBox
http://www.geocities.com/richtoybox/index.html

"hviking" wrote in message
news:QIqXc.11774$Nn2.3578@trndny05...
Hi today went out to check on fish and found pond down about 12 inches of
water.

How does this happen and how do I figure out what's going on?

Water level was constant for last couple of days. Checking the drain time
now very carefully. What should I be looking for?

If I have to replace pond liner, i have a rubber liner in a free form
pond.
What is better a free form or a tub that I've seem in the shops.

Also how long does a plastic liner last??