Pond specifics (see photos below):
- 2,000 gals
- 5ft deep at the deep end (opposite end from waterfall)
- straight sides, no rocks (except for the border), no plants
- 2 separate filtration systems- one biofalls (mechanical filtration is 8 layers of quilt batting sandwiched between 2 filter pads), and biological media is pea gravel, along with bacopa plants. The 2nd filtration system is a 55g barrel upflow system; mechanical filtration is exactly as above, biological filtration is several bags of kitchen scrubbies. Each system is powered by a 2800gph pump; each has a retro bottom drain that takes water from the deep end of the pond
- 400gph UV filter, apropriately diverted to allow for efficient UV action
- several koi- 8" to 24"; the quality of filtration is such that ammonia and nitrites are always 0, pH in the 8 range.

My problem is that the water level consistently falls 6", then levels off (doesn't fall any further). I thought at first that there was a leak, but even after pulling back all the rocks around the border, inspecting the waterfall, inspecting all plumbing and connections, etc, there is 0 evidence of a leak.

I read a response by Mike_Il to another poster's issue, where he said this:

"As far as the batting goes there is no drag on the pump what will happen is the water level where the pump is will drop as the batting gets dirty. At first there will be almost no drop but as the batting gets dirty the level will continue to drop until the pump sucks in air."

Thinking that this was related to my issue, I changed out the filter pads and the QB from both filters, and as part of the annual cleanup, vacuumed the floor and did an 80% water change.

Subsequently, the water level still falls- but whereas before it fell 6", it now falls 3" before leveling off.

I was admittedly ignorant about the fact that the filter pads and QB being clogged has a direct impact on the water level, but clearly it has some impact. But what else is going on why the water level is still falling? Is there too much mechanical filtration?

The water level did this for a significant portion of last summer (2 months or so), and then abruptly one day, it stopped falling. It recently started up again late this fall; this leads me to believe it is not a leak.

Anyone with any insight? I'd be ecstatic to hear it; if I had any hair, I'd be pulling it out at this point. Thanks in advance.

Brian.

Sorry I can't help with your water level falling.

You seem to have quite a lot of vegetation running up to and into the pond. That could account for at least part of the problem.
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The vegetation (bacopa) was there from last year- it became overgrown and I finally gave away most of it. It was already gone when the problem started occurring.

A couple of questions if you wouldn't mind answering. In the pictures I see a pipe underwater so I assume that this goes from a bottom drain to somewhere. The question is where does this pipe go to? How does this pipe get out of the pond? How far below the water level is the shelf that the rock sit on? Where are the two 2800 gph pumps located?
Mike

The pipe that you can see is what feeds the biofalls. It goes from the bottom of the pond (retro drain- sits maybe 3" from the bottom) to a priming pot, to a 2800 pump, then to the biofalls (with some diverted to the UV filter). It's a 2" pipe.

The other pipe that you can't see is a 1.5"; it is also a retro BD (about 4" from the bottom), and it goes from the bottom of the pond, to a priming pot, to the other 2800 gph pump, to the 55g barrel filter, then back to the pond (you can see the return at the left side of the pond).

The 2 pumps and the 55g barrel filter are located above ground, around the corner from the pond- maybe 8ft away.

The rock shelf is almost the same as the water level- it was just done to hide the liner. If you're looking at the 2nd pic from the top, for example, you can see the rocks on the bottom right of the pic; that's the level of the shelf.

Beautiful pond!

Sorry I can't help with your water level falling.
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Thanks for the compliment- that's very kind of you.

Even with this issue, my wife has a hard time getting me into the house :-)

Even though the cold (for us anyway; 30 degrees or so) has me inside today :-(

How fast does the water drop 6 inches? Does it drop with the pumps not running? What is the surface area of the pond?
Mike

Very difficult to tell how much it drops with the pumps not running, because of the fact that the water slowly drains back into the pond from the 55g barrel when it's off. But I have not tried turning each system off and looking at the effect since changing out the MF. That should be something I try, so hopefully I'll have a better answer for that within a couple of days or so.

Pond is 10ft x 7ft, so the surface area is 70sf.

The issue of clogged pads in the other post was with a settling chamber where as the pads gets clogged less water is able to get to the pump on the other side of the pads thus the water level where the pump is drops because water can't get to the pump as fast as it is being pumped out. How could cleaning your pads cut down the water loss in the pond? The only way that I can think of that this could happen is that when the pads are dirty the water goes up the sides of the container and over the top of the container. When the water level in the pond drops 6 inches the suction of the pump has to lift the water higher and the head pressure increases a little over 6" which will drop the out of the pump to the point where it might not overflow. Then when clean pads are used the water goes through the pads and not up the sides thus the water level isn't quite as high at the edge of the container and the output does not have to drop as much for it to stop overflowing the container. Is this possible? I would say that yes it is possible but not likely.
Mike

I am sorry but I don't make guesses until I have all the information I can get. So I will tell you what I would have a client do with your problems. I usually have the client make the observations as they are easy to make and but are made over a period of time. The first thing I would do is stand a ruler up in the pond so that the ruler is partially out of the water. This makes it very easy and accurate to measure the drop in the pond level. Then I would fill the pond full and record the measurement from the ruler. Then with everything running come back and record the water level and the time. These observations would be no sooner then 4 hours apart but not longer then 8 hours apart. When the water between two measurements doesn't drop then I would refill the pond and turn off the biofalls. Repeat the measurement process and repeat with the 55 gal filter off. These measurements will help pinpoint where the problem is. It will also tell if the leak is at a constant rate and how large an area the water is getting out. The first set of measurements will confirm that there still is a problem. The next two will help tell us what part of the system is the problem. The time between measurements will allow us to know how fast the leak is letting water out of the system and if it slows down when getting close to the leak point.
Mike

Mike

But you're right- if I empty and clean out both filters at the same time, starting them up again drops the water level about 3" immediately.