I'm going through the same problem you are right now. I did find a place yesterday morning where the water was siphoning out from a fold in the liner. I packed some soil behind the fold to bring it above the water level, and assumed that would take care of the problem.

Nope, water is down again this morning, so it appears my problem was two-fold. I found one of them, but still have another leak to find.

Wicking from plants can cause some leakage, but plants like WH don't consume enough to bring it down all that much. Unfortunately.

So, since I can't find any leaks in the stream (the usual culprit), it looks like my weekend is going to be spent trying to find that other leak. Guess at this point I'll have to check the face plate of the skimmer, the joints in the plumbing, etc, since I can't find any more wet spots on the soil around the edges. I'll find it eventually, but it may take some time. This is the frustrating part of owning a pond.

Chris,
Will WH evaporate water quickly? The answer is they can. At my shop I have a vat that is 25 ft x 4 ft wide that is full of WH and water level is at least 4" from being able to over flow. Some days there is very little evaporation and on other days the water level can drop .5" to 1" a day. There is no water movement in this vat to cause a drop so the only drop can be evaporation.
Mike

Nancy, I have found that using a caulking gun to pump silicone seal into the liner folds, where they were acting as a siphon and drawing the water out. The silicone seal plugged up the tube like fold and stopped that capillary action.

It always seemed to happen, after we had heavy rain or a thunder storm and the pond filled up to the edge, that the siphoning action, caused by the folds, carried on draining the water out of the pond until the level went down below normal.
"Horton"

We had a leaking problem also. During the winter the pond would drop to the level of the Sluices and stay there, Once the pond was in operation, we would loose the equivalent of an inch or more per day.

What was happening was the discharge from the pump was increasing the level on the side opposite the discharge pipe so that it was going over the top of the liner. The apparent pond level was unchanged.

Once we installed a smaller pump with lower flow the level at that point stayed below the top of the liner.

I suspect you cold do the same thing by redirecting the discharge, or discharging in a fountain

Thanks for the suggestion of plugging the fold-tube in the liner, Horton. I found several of those that had never been a problem before, but have been lately.

Still losing water, though. I've left it alone to see where it stops, and since it's still going, my thought is the main culprit is in the plumbing. So, guess how I get to spend my weekend? :-(

I found the article very useful in the link below. I know a few people who have had leaks in there folds and seams. I am building a pond now and one goal was to has minimal seams and as flat as possible. I have only 5 creases and seams in the pond each corner has one seam except for one which was oddly shaped and too difficult to only use one seam. The seams are taped in place using double sided EPDM tape and primer and a sealant is used in the seam to prevent any water from getting into the folds.

Here is a link that might be useful: Finding Leaks in your Pond

Nancy, I read your other post about finding the leak. Isn't it great when you finally pin point the culprit and the frustration goes away, good for you!

Woeisme, that is a well written and informative article you posted the link to, about leaks and how to find them.
It covers the subject, about dealing with pond/waterfall leaks, really well.

They can drive a person crazy, trying to locate them!
"Horton"

Thanks, That is a new pond forum that a freind of mine set up. It is pretty informative and the moderators do not allow blasting. It has a few seasoned pond veterans on it as well as noobs. It is only a 2 weeks old, but is growing daily. Check out some of the DIY's. A well know pond equipment vendor is a member. He gives discounts to members. I got some real good deals from him, way under anything you'll see on the internet or eBay.

*Update*

Thank you for all the advice/tips. I shut off my pump for a day+ and measured the level of water in the pond. It literally didn't move, so I now know that the issue is somewhere between the outbound pipe from my pump and the last waterfall into my pond. My wishful thinking that is was my water hyacinth was incorrect. I adjusted one section of my stream and am waiting to see if that helps. I'm only updating this in case someone else is experiencing the same frustration that I am. Good luck to my fellow leakers... :-)

-Chris