Any deer on the property?

Here is a link that might be useful: My pond the way it was before the freeze.

Yes there are deer, but the plants are not disturbed at all that I can tell which left me to believe that it wouldn't be deer. Not to mention we are probably talking 50ish gallons of water. I kind of ruled that out....

You say you have two levels. Do you have a waterfall? I've had situations in the past where the waterfall was being deflected by a stray leaf or blade of grass. The water would be dripping out of the pond and emptying the system. Sometimes the offending situation clears up before you notice, like the leaf or grass breaks or moves. Be sure that nothing can be wicking the water out or deflecting the water out. I have a 100 gallon preformed pond and a small deflection of water can cause a major drop in water level in a short time. Hope this helps.
Deb

No waterfalls. I want one eventually, maybe when I tear up the hard plastic tub and dig out a bigger liner pond next year. I should have clarified, its one of those 100G ponds you get at the big box stores. The outer portion of the pond is half the depth of the inner section. I even put the filter outfeed tube down into the water so I could rule out water splashing and evaporating quickly. I think I might just keep the water slightly above the lower depth so I don't have fill it up so much, but the plant roots still have plenty of water.

Nick, your problem is a strange one. Hot days can lower my water level by a few inches, but nothing like the loss you are describing.
A leak would produce a steady loss over a period of time. Again, nothing like your description.

It sounds like water is being removed from your pond by some one, or some thing.

Could simply be a good ole crack in the bottom that waits for the right temperature to open up.I have a plastic watering can with a hole in the bottom that doesn't leak if there is a leaf over the hole but empties in a minute if I clean it out.

I had the same situation when I moved into my house last year. Same kidney shaped 100G pond that would empty every week or so. Turned out that it was the pump. When the pump filter got clogged it would shoot water out of the valved pipe that was feeding the spitter. I got a mechanical filter to attach to the pump that never got clogged and that fixed the problem.

In the last few days though it's been draining again and for the life of me I can't figure out. I filled it last night and it was already half empty by tonight.

Nick,

Sounds like the very same problem I just experienced with my preform of 7 years. Water okay one day, next day 6-8 inches missing. WELL, several days ago when I woke up, I could hear a water sound and it was not the smooth quiet sound of my bubbler... It was the bubbler shooting water 3 feet in the air! My pond had drained completely with the exception of 3-4 inches. Thank goodness I was home when this happened as I was able to save my fish. I removed the fish, turned off the bubbler and waited a day to let the pond continue to drain hoping to find the leak. Low and behold, a LARGE ROOT (from Trumpet Vine) had pressed so hard on the lower wall that the plastic split. I'm sure this had been going on for quite a while but the crack would probably fill and stop...then leak again. This was going on with my preform for 2 seasons....curious water loss.

If you turn your bubbler off, stop adding water (remove fish if need be) and wait, the water will drain to below the leak if it's on the side walls. If it's in the bottom, it will drain completely.

I am now in the process of replacing my preform with a POND LINER..... It's a lot of work, but much easier than another preform. And of course, the next project will be to KILL THE BEAUTIFUL TRUMPET VINE. I'm sure your loss is from either a root cracking the side wall or a large rock being pushed into the wall or bottom. Either way, if you find the cause, YOU DO NOT WANT TO PATCH A PREFORM as you will be going through the same thing...not good to patch a preform from what I've read.

Hope you find the leak.... there's definitely a crack somewhere, hope you find it soon.

Hi
Just recently had a similar problem with an L shaped lined pool. has been running about 7 years without a problem.
In Jan . it suddenly dropped around 10 inches filled it back up and the next day there was only around 5 inches of water in the bottom lol.
Decided I obviosly had a serious leak so removed everything but couldn't get another liner right away so filled it back up and it hasn't leaked since lol.
Been over two months now without a leak . I'm realy perplexed lol. I got a new liner but now I'm curious to see what's going to happen lol. i suspect it's a root that has penetrated the side and then filled with silt. I only use it for plants so if it fails again ,no big deal.
gary

Well I'm still just baffled by it. I totally took out the filter to make sure that wasn't an issue. I have a couple freshwater clams in there that I got from the river that do a good job of filtering. The last time it did that I drained the pond to a couple inches under the lowest its ever drained too and took out all the plants and such. I couldn't find any trace of a crack or hole. I filled it up just a few inches above the upper level and put all the plants back in (still have the filter out) and its been over a week and hasn't dropped. If it was a crack I'd think that it'd keep draining until all the water is gone once it "opened up" It is very interesting to see that others have similar issues with their ponds. At this point I'm going to see how long til it drains again. Maybe with less water in the pond creating less pressure it'll stay fine. I just wanted enough on the second layer to keep the plants roots wet.