Retrofitting pond with bottom drain

[Virginia ranchu]

I have a rectangular pond 8'x12'x2' deep that has a skimmer at one end and a "biofalls" filter at the other, and the bottom is covered with large, egg-sized river rock. The water stays clear, but after several years, there is a lot of muck on the bottom. I am considering adding a bottom drain, that would feed a PVC pipe run along the bottom of the pond (internal). I am not sure whether to purchase an additional filter to capture this bottom muck, or to just build a settling pond. My idea is to build a rectangular bench-like structure from lumber, which would have two internal sections lined with a pond liner. In theory, the muck would collect in the first chamber and the clean spill-over would go to the next chamber and then back to the pond. BTW, the pond is surrounded by a stone patio, so I cannot excavate to accommodate any in-ground solution. Any comments/suggestions would be appreciated.

thanks,

Rob

[SeaWitch]

I have a rectangular pond 8'x12'x2' deep that has a skimmer at one end and a "biofalls" filter at the other, and the bottom is covered with large, egg-sized river rock. The water stays clear, but after several years, there is a lot of muck on the bottom. I am considering adding a bottom drain, that would feed a PVC pipe run along the bottom of the pond (internal). I am not sure whether to purchase an additional filter to capture this bottom muck, or to just build a settling pond. My idea is to build a rectangular bench-like structure from lumber, which would have two internal sections lined with a pond liner. In theory, the muck would collect in the first chamber and the clean spill-over would go to the next chamber and then back to the pond. BTW, the pond is surrounded by a stone patio, so I cannot excavate to accommodate any in-ground solution. Any comments/suggestions would be appreciated.

thanks,

Rob

I can't offer any suggestions as I am new to ponds, but I sure would like to see your pond if you get a chance to post some pictures.

[bekko]

Rob.

You want at least fifteen minutes of retention time in the settling chamber; thirty minutes is better. Have the water enter the settling tank about one-third the way up the side of the vessel (not at the bottom and not at the top). Brushes or Matala mat would improve sedimentation, but complicate cleaning the settling chamber.

It works best if the settling chamber is gravity fed. If the settling chamber is fed by a pump, the coagulated solids are ground up by the pump and sedimentation is not as efficient.

You can also use a bead filter to capture solids.

Capturing the solids is only half the problem. You first have to get the solids to migrate to the intake pipe. When the pond depth is at least two-thirds the pond width (as in a koi pond) this can be done with tangential flow (swirling the water). In a shallow pond the whole pond is acting as a sedimentation chamber and it is difficult to get the solids to move once they touch the bottom and are coagulated by bacteria. Removing the stones would help, but may not be practical for aesthetic reasons.

A monthly once-over with a pond vacuum may work better for about the same amount of effort.

-steve

[mikroll]

hi rob,
take a look at this site for ideas about settlement style filter systems.
http://www.hendersons.co.uk/filtration/page2.html

[Virginia ranchu]

Steve and Michael,

Thank you both! This is great information. The challenge will doing this economically, and with a solution that isn't too unattractive,

I do have a pond vac, and I have used it, but it is a weird one that only runs until the body canister is full, then it shuts off and drains itself and then starts up again. It takes forever to get much vacuuming done.

Cheers,

Rob

[BruceP]

Rob....... I have built something like what you are talking about and it is running on a 1000gal indoor wood framed tank. Mine is built above the tank and is pump fed . I dont recall seeing if your pond is inground or above. If it is above ground you could gravity feed it and pump return it.
Here is how i did mine. I got a round heavy rubber bowl used to feed cattle about 16" by 5" deep. Place a 2" line from it, turned it bottom side up with three 1" spacers on the rim, ran over the side of the tank and down to a pump on the floor. Pump pumps the water up to the filter box I made from 2x4, EPDM rubber lined. I have the box divided into 3 chambers, dividers made out of fiberglass sheets and held in place with aluminum U channels. First divider is set to the bottom so the water flows over it and the other divider is set high so water flows under it. Water is pumped into the first chamber which has 4 sheets of Matala on edge so the water has to pass thru them and over the divider to the second chamber which is filled with plastic carton strapping(bio). Water then flows under the second divider and up thru Bioflow9 media which is aerated with an air disk in the bottom of that chamber. Water exits that chamber at the top and gravity feeds back to the 1000g tank thru a 3" spray bar.
Reason I built it this way was that having the filter tank above the tank I saved floor space and also I didnt want to drill holes thru the sides of the tank because this is in my basement and I felt safer this way.
If you used this system gravity fed you could incorporate a pump after the filter tank and pump back to the pond in various different ways, TPR, TT, spray bar, etc.
Just food for thought.. :)

ps: Remove the ROCKS!! ;)

[Virginia ranchu]

Hey Bruce,

I like your design for the bottom drain (upside down bowl). My pond is in-ground, so I couldn't do a gravity fed system. I would have to get a submersible pump and pump the water up to the settling chamber.

I have another idea though. The pump from my current system is in the sump beneath the skimmer intake at the end of the pond. I thought about inserting a "T" or "Y"adapter where the outlet from the pump connects to the return line. I would then run a pipe from the T adapter to the bottom drain. My hope is that this would create enough suction to draw water from the bottom drain.

thanks for your ideas.

Rob

[BruceP]

Rob...... the tank I have this running on is using an external pump with a swing check valve below water line in the tank. Outside the tank I have a ball valve so I can shut off the circuit if needed.
One of our outside ponds I have the same type or retro bottom drain running to an external pump and then up to 2 55t barrel filters gravity flowing to a skippy and they back to the pond via waterfall and one tpr. Again I have a swing check valve and ball valve to keep it primed... I should mention that I have priming/straining pots before each of these pumps. I use external pumps wherever I can as they are much more efficient to operate and you get alot more flow per amp.
Your T or Y idea is only semi correct. The pump will draw water from the source of least resistance. I 'think' that would be from the skimmer and not draw from the BD (bottom drain). However, if this is a box type skimmer, you could put a pipe from the BD into the skimmer box. Then the pump would naturally take out the volume of the skimmer box and the BD would flow into the box. I know this has been done by others successfully. Guess it would all depend on the type of skimmer you have and how much water your pump draws. You perhaps could use a larger internal pump to feed your existing filtration plus the added flow of the BD to your box style filtration.
More to think about.... :)