So You Want a Crystal Clear Pond – A (nearly) maintenance-free system for clean, beautiful water

pondfiltration When I was asked to write about what
it takes to have a crystal clear pond,
a lot of ideas came to mind. This is a
topic I could easily write an entire book on and
still only scratch the surface. So instead of glossing
over all the factors contributing to a crystal
clear pond, I will focus on the most important
one: filtration.

There are several different types of filtration,
but the two that will have a major impact on the
clarity of your water are mechanical and biological.
While both of these filtration types can be
man-made or naturally made, I am going to
cover man-made filtration specifically.

Of course, just because we are building the
filter doesn’t mean that we can’t use natural
materials for the media. Thus, I’ve chosen to
write in detail about a natural media that, in a
lot of circles, may be considered a dirty word:
rock and gravel.

Almost every gravel area that you see is either an undergravel grid filter or upflow gravel filter. Everything is run off air lifts.

Rock and Gravel

A very old type of filtration media,
rock and gravel were used for a long time
but have lost favor with many ponders.
One of the reasons for the falloff is that
the surface area per cubic foot is not very
high — or so people think. Yes, rock is a
solid material that takes up a lot of space,
but it is also a natural material that’s
formed on a very fine structure and then
is eroded on a microscopic level. With
that in mind, the surface would have
a fairly high microscopic surface area,
which is never included when talking
about gravel surface area.

Even taking that into consideration,
a filter using rock or gravel will require
a larger footprint to handle the same
size pond as some of today’s newer
medias. But the smaller the filter, the
more frequently it requires maintenance.
Thus, the small amount of maintenance
required to maintain many rock or stone
filters is not easily accomplished with
other media.

Rocks on the Bottom

When we talk about putting rock and stone on the bottom of the pond, we immediately stir up passionate feelings in some people. There is a lot of debate about
whether a pond should have stone on the bottom, and the argument boils down to the buildup of debris in the gravel.

To speak to this issue, let me tell you about a pond that I am very familiar with
— a pond I built 22 years ago! This pond is six feet deep and has about six inches
of gravel on the bottom that has never been cleaned.

Now, I know what you’re thinking: “There must be a whole lot of debris in that gravel.” But when I swam in the pond last year, I dove to the bottom and dug in the gravel … and there was no debris to be found! How is that accomplished? The secret is an undergravel suction grid system. If designed correctly, it performs
excellently with very little maintenance.

An undergravel grid is being installed in an existing pond. The old gravel is being reused.

Undergravel Suction on a Small Scale

What is an undergravel suction grid filter? Well, most of you are familiar with its smaller counterpart: the undergravel suction filter in aquariums. A filter like this is built with thin slots in the plate, which is supported off the bottom of the aquarium. Small gravel is placed on top of this plate, and water is sucked through
the gravel and the slots.These filters work great for a while, but then they need to have a lot of maintenance done or they fail. By “maintenance” I mean the gravel on top of the filter suction plate has to be cleaned.

Anyone who has done this maintenance on his fish tank knows it is not a funchore. In a busy aquarium full of life, waste and debris quickly build up in the
slots, causing the gravel to clog up faster than you can (or want to) clean it.

Ponds vs. Aquariums

If we want this type of filter to work in a pond, we have to look at why it has problems in an aquarium.

The real difference between the undergravel grid in a pond versus in an aquarium is the space in the grid. In the aquarium, the space between the pieces of gravel and in the slots in the suction plate is very small compared to the waste produced. In order for the system to allow water to flow through and not clog up, the waste has to be
almost completely eaten by bacteria. This process takes longer than it takes for the gravel to clog up. Therefore, the filtration simply cannot keep up with the waste. The filter clogs up and fails.

To avoid this problem in the pond I
built, I designed the undergravel filter to
have a series of pipes on the bottom with
⅜-inch diameter holes drilled in them.
The pipes were buried in .- to 1-inch
round gravel with about two inches above
the pipe. The spacing between the pieces
of gravel is fairly large, and the holes in
the piping are large compared to the
waste to be broken down. All the holes
in the suction pipes are six inches apart,
providing the waste a lot of area to fill.

An undergravel grid installed and ready for gravel.

In this grid there are six inches in
every direction that would have to clog
up before this filter would need to be cleaned on every suction line. Of course,
if this filter were only a small part of the
bottom of the pond, then there could or
would be enough waste to clog the grid
before the bacteria could break it down
enough to get rid of it. Therefore, the
larger the area of the pond’s bottom that
can be part of this filter, the better.

Will this filter ever clog and need
cleaning? The answer is yes, but the better
question is: How long will it take? There
is no set answer. It all depends on how
much debris or waste is being put into the
pond (or being made by the pond).

Success Story

Earlier I wrote a little about the 22-year-old pond with a gravel bed that has never been cleaned. This happens
to be my own koi pond and my design. Located in Batavia, Ill. (about 35 miles west of Chicago), this pond was built to
be as maintenance-free as I could make it.

No, it is not completely maintenance-free
… but it is close. It is about 18,000
gallons and requires an average of three
minutes of maintenance a week. None of
the maintenance is spent on the undergravel
suction grid filter. The pond has
never been emptied or cleaned since it was
built. Based on what I have seen, the filter
will not clog up as long as I am alive or as
long as the liner lasts. My guess is that the
liner will last for another 25 years.

I did make a mistake when I designed
and built this pond. I used .- to 1-inch
round limestone gravel. The problem is
that after 22 years, the limestone gravel
is shrinking in size. I believe I may have
to remove this gravel and replace it with
gravel that takes longer to erode.

Of course, I never thought that the
filter would go this long with no maintenance
required. Sometimes you stumble
on the right combination of ideas and
designs and things work far better than
expected! Is it working in Illinois because
of the climate but possibly would not work
elsewhere? I would say no; I just returned
from California, where I saw a pond that’s
about six years old and has one of these
filters. It is over-stocked with koi, and they
eat well. But the grid is working great and
has not been cleaned. I saw this pond two
and a half years ago and it looked good
then — but it looks even better now.

Half the bottom of this pond is undergravel suction grid, and the other half is undergravel pressure grid filter — all being run off submersible pump.
Half the bottom of this pond is undergravel suction grid, and the other half is undergravel pressure grid filter — all being run off submersible pump.

Will this design work in every situation?
That I can’t answer, because this
type of filter hasn’t been used in every
possible circumstance there is. But it has
worked perfectly every time that I know
of it being tried!

I have also used this system as a pressure
undergravel grid filter, and it has
performed perfectly for the last seven
years. The only complaint from that
customer is that the water is too clear. A
suction undergravel grid filter normally
uses an external pump or air lift system
to run it, but a suction filter can also use a
submersible pump. A pressure undergravel
grid is built similarly to the suction grid,
but water is pumped through the grid.
The pond that is pictured above uses both
suction and pressure undergravel grid
filtration. The picture was taken when the
pond was five years old. Both systems are
being run off the same submersible pump.
This is a very formal pond and we kept
everything inside the pond.

Versatile and (Almost) Maintenance-Free

In conclusion, the undergravel suction type of filter I’ve described will give you a
great mechanical and biological filter. It is hidden in the pond and doesn’t require an area larger than the pond. If done correctly, it has proved to require little, if any, maintenance.

It can be used with either external or submersible pumps. It also works great with the latest air lift technology. I don’t know if “the perfect filtration system” really exists. But this one comes close enough for me.

28 Responses to So You Want a Crystal Clear Pond – A (nearly) maintenance-free system for clean, beautiful water

  1. dominic carone June 11, 2016 at 12:03 AM #

    Great article Mike. Nothing like and under gravel suction grid!

  2. Suzanne July 28, 2016 at 3:48 AM #

    I have a few questions about the picture of the very long and narrow “under gravel grid installed and ready for gravel”. What size pipe did you use? Did you also drill three 3/8 inch holes every 6 inches as you described in the 22 year old pond that you built? What size pump did you use? It seems to me that it would take a huge pump to create enough suction for all those holes and for that large of an area. Can you expound on that?

    • Mike White July 23, 2017 at 9:18 AM #

      Hi Suzanne, I did not build that long narrow pond that is pictured. That was Eric Triplett “The Pond Digger” out of California pond. I did help with the design of it. Yes it was made with 3/8″ every foot. The three inch pipe was used to handle the flow from the pump. On Thursday of last week Eric was out here to take a underwater video of that now 24 year old pond. The problem was that Wednesday night we had a bad rain storm and the pond pumps lost power all night. Between the 2 inches of rain we got and pumps being off when everything got started back up at 7 am the pond was pretty cloudy when Eric got here at 7:30 am. He said he would have to come back and that the video. I took him out to breakfast. When we came back less then a hour later the pond was clear and he took the video.

  3. Lora Lee Gelles July 28, 2016 at 9:21 PM #

    From Mike White:
    The size of pipe is 3″ PVC with 2″ lines going off to the sides of the pond. The holes are 3/8″. The surface area of all the holes drilled should be at least 5 to 10 times the surface area of the cross section surface area of the pipe. Each 3″ line has it only pump running the line. Each pump is moving about 7000 gph. The size of the main suction lines is determined by the amount of water the pump is moving and the volume of the pond. The nice thing about this system is that it is a self adjusting system. The flow rates at different points in the system change constantly. Where the flow rates are higher more debris will be sucked causing more restriction of the water movement causing the water flow to change somewhere else.

  4. Ed OBrien September 19, 2016 at 9:21 AM #

    In the main suction line are there holes drilled the same as in the legs, or are they left solid?

  5. Edward OBrien September 19, 2016 at 3:53 PM #

    I have a couple questions.
    Are there holes drilled in the central suction pipes, like the cross tubes?
    Do the holes in the pipes face up or down?
    I have a pond that is about 2600 gallons, built about 12 years ago, and want to upgrade all the filtration systems, and your help would be greatly appreciated.
    Hindsight is 20 20, wish I new this info back then!

    Ed OBrien
    New Jersey

    • Lora Lee Gelles September 25, 2016 at 8:56 PM #

      From Mike:
      Yes there are holes drilled in the central suction pipe. All holes are drilled in the bottom of the pipe. The reason for this is so the system can remove debris all the way to the bottom of the pond. Also it uses the entire bed of gravel. This way the gravel will stay clean as there is no where that doesn’t have the potential of water moving through it.

      I like to have as many holes as possible. I like to have the area of all the drilled holes being ten times the area of the cross section of the main suction line. This allows the filter to automatically adjust it self depending on how much debris is in the pond. The one thing that is difficult to control and is hard on the system is leaf debris settling to the bottom. This can effectively block the flow of water through this section of the filter. In the northern climates this usually happens when the system is either shut down or going to be shutdown soon.

      • Ed OBrien September 27, 2016 at 3:18 PM #

        Thank you sooo much for the info. I will send photos when I am finished!

  6. Karl November 3, 2016 at 7:28 AM #

    I’d like to know if I have a 4000 gal pond, with an 8500 gph external high head pump, would I have to have a separate pump for the under gravel filtration system from my waterfall? The pond is 50ft long by 3.5 ft wide and 2-3 ft deep along most of it. Top of falls is 5ft above waterline and need about 5000gph coming out of a 32″ diffuser. Appreciate your input!

    • Mike White July 23, 2017 at 8:57 AM #

      Hi Karl, I am not sure if I understand the question. The under gravel grid filter would go to the intake side of the pump. Would you require a second pump? That would depend on what else would you want this pump to run. I would want the 5000 gph to run the suction grid at a surface area of about 175 sq ft. Having an 8500 gph “high” head pump I would not want to drop the head pressure down to get the 8500 gph that the pump might be able to pump as the pump motor will over heat.

      Mike

  7. Jeff Higgins March 30, 2017 at 7:20 PM #

    I’d like to know what you are doing to catch all the debris being pulled out? Basically, what are using, settling chamber or some type of material removal?
    Thanks
    Jeff Higgins

    • Mike White July 23, 2017 at 8:43 AM #

      Hi Jeff, We use skimmers to remove surface debris. Sticks or branches have to be physically removed. Most other organic debris will break down by itself and not be a problem.

      Mike

  8. Tim Camp March 31, 2017 at 4:44 PM #

    Great article ,Mike. I have a customer with s very formal pond , similar to the one pictured. I’m going to show him your article and try to sell him on your system.

    • Mike White July 23, 2017 at 8:44 AM #

      Hi Tim, If there is anything I can help you with let me know.

      Mike

  9. Tymber April 12, 2017 at 12:48 PM #

    Hi Mike,
    Thank you! I currently run a gravity return bog/natural pond that has been a huge success but am moving to a self contained above ground tank and want to use the undergravel grid filter, all contained in tank if possible. This is terrific info on the grid construction, thank you! I just can’t seem to get clear on in and out points of water & suction vs pressure (using submersible pump). Can you help?

    • Mike White July 23, 2017 at 8:37 AM #

      Hi Tymber, Yes it can be hooked up to a submersible pump. You could connect the suction grid piping directly to the intake of a submersible pump. But that is asking for problems. You will probably get something bigger then the pump can handle entering the pump. You might be able to pipe a leaf basket used on external pumps to catch anything before the pump. What I usually do is use a pump vault that I can seal. I put the pump in that and then pipe the grid to dump into the vault. The output of the pump is then piped thru the vault to where I want the output to go. When the pump is turned on then the only water the pump can pump is water that is getting into the vault from the grid. The only real problem with using a submersible pump is when they have to be changed. It can be difficult to remove and replace the pump underwater. I have one pond that I installed 10 years ago using this system that is functioning perfectly.

      Mike

  10. Wayne Allison April 23, 2017 at 8:39 PM #

    I have a pound about 10 ‘x15’ 2 ft deep I understand the pipe lay out confused on type of pump to use and where is the the debri pumped to can you show pics of the pump part of this system

    • Mike White July 23, 2017 at 8:22 AM #

      Hi Wayne, Normally an external pump is used with this system in which the plumbing is simple. The underwater grid piping goes out of the pond and then connects to the intake of the external pump. It can be connected to submersible pump but it is a little more difficult. See my response to Tymber question.

  11. Jacob May 25, 2017 at 6:41 AM #

    Hi,

    First thanks for a great article 🙂

    Have been thinking about updating my pond to something like this and now that I have a leak, it seems like the perfect time…

    Have always had 100% clean water = I can see small stones on the bottom of the pond almost 2m down..

    My pond is split up in 2, I have a root zone (lava rocks and plants) size 180x220cm and it’s 40cm deep, here all my water pass after the filters and then ends up in the main pond size 190x220cm and is 190cm deep. What I like to do is to use less mechanical filters = only keep my Laguna Pressure Flo 4000 as it is very easy to keep 🙂

    Questions that I hope you can answer:

    1. What amount of gravel do I need to add on top of the pipes, if I add this to the main pond?
    2. Will my pond be a good fit for this type of solution if I ask you?

    Thanks
    Jacob

    • Mike White July 23, 2017 at 8:07 AM #

      Hi Jacob, I will answer the second question first. The pond being 6.25 ft x 7.25 ft the underwater grid filter will work perfectly as long as the piping is sized for the water flowing through it. The amount of gravel is determined by the size of the pipe used in the grid. In your case you might use 1.5 inch pipe for the grid. The outside diameter of that pipe is a little bit smaller then 2 inches. Assuming the pipe lays on the bottom then you would need a layer of gravel 4 inches thick, O.D. of pipe plus 2 inches on top of pipe. In your case about 15 cubic feet of gravel.

  12. marco millet May 26, 2017 at 11:20 AM #

    We just have highly alkaline lime stone gravel in my state and any other like lava rock or river rock cost 15 to 30 times more. Its fine to use lime stone? thanks for your help.

    • Mike White July 23, 2017 at 7:50 AM #

      Hi Marco, Limestone gravel is not my first choice. The pond water will slowly dissolve the limestone gravel. If the water being used in the pond is not normally hard the limestone will make it that way. My own pond I used Limestone gravel 3/4 to 1″ round. The hardness of the water used for the pond is 450 ppm so the gravel didn’t change it.

  13. Cameron July 4, 2017 at 4:37 AM #

    Hi Mike, I just have two questions.
    What kind of gravel do you suggest using?
    What would be the optimal gravel size?

    • Mike White July 23, 2017 at 7:43 AM #

      Hi Cameron, My original pond that I built 25 years ago I used 3/4 to 1″ limestone round gravel. It worked beautifully except the water flowing thru it was dissolving the gravel. Last year I had to put a layer of 3/4 to 1″ round granite on top of it. I normally use 3/4 to 1″ round granite gravel. I did build one formal pond with pea gravel. That was 10 years ago and it is still working perfectly. The hole sizes and number of holes had to be modified.

      Mike

  14. Ben Bowen July 27, 2017 at 5:46 PM #

    Considering just filtration (not aesthetics) is there a clear winner between round rock and a fractured gravel?

    • Mike White July 27, 2017 at 6:34 PM #

      Hi Ben, I have never used fractured gravel before so I do not know. I would be afraid that there might be problems because of the small spacing between rocks. The one time the customer wanted me to use pea gravel I was afraid that it would fail but that was 10 years ago and it is still working with no problems. So I do not know how it would function. If you try it let me know.

  15. Hamid August 9, 2017 at 10:07 AM #

    Thank you Mike. I have been trying to find ways to make my fishpond water clear. Barley straw, the chemicals, and submerged small filter boxes have not worked . I want to try an external pump. What kind of pump are they?, what do you suggest?
    Finally: do I still need to use some sort of sponge type filter in addition to the gravel?. Thank you again

    • Mike White August 10, 2017 at 4:13 AM #

      Hi Hamid, As far as a pump goes it depends on how much water you need to pump at what head pressure. I am not going to suggest a brand pump. There are a lot of different brands out there and some work better as far as how they will perform on your circumstances.
      On any external pump you are going to want a leaf basket before the pump to protect the pump. Some pumps have the built in. If the pump is above the water in the pond then you are going to want either a self priming pump or a good check valve in the system so the pump will not loose its prime and damage the pump. I am sure there are articles that will help you decide on what pump to get for your circumstances.

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