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Pond Construction 101
Bad Information Resources – “Natural” Does NOT Mean Healthy
by Cecil Ferguson, The Pond Doc
Last Revised 11/12/2006
Many people who are in the market for equipment and resources for building a goldfish, koi or garden pond use the internet for researching instruction on how to design and construct it. There is good and bad information to be found on the web. Unfortunately the internet is filled with information that is inaccurately stated by companies hoping to sell product, old-school pond builders who have closed their minds to other methods and writers who use these same sources and are not receiving the best of advice. The best way to dodge these bullets is to use common sense and think a little deeper about what you are attempting to build.
The most widely used concept of pond construction emphasizes copying nature. This is an appealing idea -- after all, most backyard ponds are created to bring a little nature into the home environment. Our intention is to make our pond, waterfall and stream look and act just like it was built by Mother Nature herself.
Here’s where bad information runs rampant! For literally decades the art of pond construction meant copying nature exactly. The thought has been (and still is on many websites) that ponds do not need an artificial filtering system because natural lakes and streams don’t have filters. In nature water is filtered over rocks and through plants so if your pond has rocks in the stream and pond and plants then your pond is filtered “naturally”.
We dig ourselves a hole, drop a rubber liner into it to hold water, add a pump to circulate the water down a waterfall and/or stream – add rocks to the bottom to hide the liner and plants to “filter” the water.
Gosh, it looks “natural”, doesn’t it?
Let’s think a little deeper and take it all a bit further...
Allow me to introduce a wild new concept to you: A garden ornamental rubber-lined pond that re-circulates the same water over and over again is in NO WAY “natural”.
Here’s why:
We “tire out” our pond water by re-circulating the same water over and over and over again. Natural lakes are continuously supplied with new water. This new water brings with it healthy additives in the forms of minerals such as calcium, etc., and oxygen. If a natural body of water has no source of fresh incoming water it becomes stagnant – like a swamp. It stinks and does not support the types of aquatic fish we care to have in our backyard pond, such as koi and goldfish. Without adding artificial means of fresh water enhancements to our rubber-lined ponds our ponds will become stagnant and the water stale.
Plants in the water do add organisms and filter water to some degree. They are quite beautiful and visually naturalize the pond. The usual way of planting an ornamental pond is to place the plants in thick soil in pots then lower them into the water. Soil leaches out into the water and settles onto the bottom of the pond in between all those rocks making a “natural” muck layer. Something else plants add are decaying, rotting leaves that fall, too, to the bottom and (along with fish poop and the occasional dead creature) join the muck between the rocks lining the floor of the pond. Over time this muck that is rich in decaying matter becomes a breeding tank for bad anaerobic bacteria because it thrives in low-oxygen environments. Parasites thrive as well -- a lovely addition to our “natural” pond. Since Mother Nature provides fresh water for her lakes constantly and continuously flushes out her water systems the natural checks and balances are naturally in place to prevent the build-up of bad bacteria, parasites, etc. Not so with a rubber liner re-circulating the same water. There’s no place for the bad things to go.
Plants are beautiful and wonderful in a water garden or ornamental pond. They just are NOT a good filtering source. By all means, place them in the pond and make it pretty – just don’t expect them to take the place of a good filter and do expect them to add debris into your pond.
There’s a system out there that I have never liked. It’s the side-skimmer system that pulls water from the top of the pond and re-circulates it through a waterfall “filter”. It’s installed with minimal planning and expertise and LOOKS so natural. Everything’s practically hidden, even the liner.
Lining the bottom of the pond with rock is one of the practices the manufacturers of these systems preach. Here’s the epitome of bad information! They say it hides the liner and makes the pond LOOK natural. Of course it does! Is it natural? NO. Is it healthy? NO. One problem is that the rocks take up precious space in the pond. I’ve seen ponds that started out as 1000 gallons end up as 600 gallons because of the massive boulders used to line the pond. Water volume is very important. The larger the volume of water the more stable the water parameters (such as pH, ammonia and nitrite build-up, etc.) will be.
Another problem with lining the bottom with rocks is the build-up of bad bacteria. Here, at the Pond Doc’s, we tend to be very fish health conscience and the side-skimmer system goes against all the rules of a clean and healthy pond environment for fish life. First of all, it only pulls water from the top. Remember all that muck and fish poop and decaying plant material that falls to the bottom and collects between those rocks? Well – it never gets disturbed. Even worse – the water in the bottom of the pond never gets re-circulated. Think of it this way: Would you mind if your toilet only flushed from the top? Second of all the muck that hides between the rocks become breeding fodder for anaerobic bacteria – bad bacteria that thrive in low-oxygen environments.
Once the top waters are pulled off the pond they are pumped up to the waterfall “filter”. The manufacturers label this container with only one or two little pads a “biological filter”. If I stuck a pebble in my waterfall I could also call it a “biological filter” by that definition.
We get back to the bad information available that says we don’t need artificial biological filtration in our manmade rubber-lined pond because it will “naturally” build up the “biologicals” on the rocks, in the waterfall, on the plants, yada yada yada. Heck, they even sell bottled bacteria for that! The same folks who manufacture side-skimmer systems also will instruct you to put products into the water that claim to add beneficial bacteria and enzymes that are designed to digest this muck and they claim it will also keep the water clear. It’s a form of sewer treatment and, though it can help a pond reach its balance, it’s not the miracle worker that they claim it to be. It helps but it doesn’t automatically make your pond healthy and cannot be used in the place of a good biological filter.
Let’s explore what biological filtration is in a simple, concise way. Fish poop and decaying plant matter produce ammonia in the water and kills fish. We need a good bacterium (namely Nitrosomonas) to convert ammonia to nitrites. Nitrites are still dangerous so we need another bacterium (namely Nitrobacter) to convert nitrites to nitrates (otherwise known as fertilizer). That’s about as simple as I can get explaining the nitrifying cycle which must be in place in the pond or the fish will die.
A biological filter is where these bacteria live. These good bacteria thrive in warm, aerated environments. The more places where these aerobic, healthy bacteria can thrive the better! Good bacteria grow on the sides of the pond, on the plant pots, in the streambed – anywhere oxygen and warmth touch moist surfaces. A good biological filter will have lots and lots of these surfaces and to the untrained eye the amount of filtering material will look like overkill. For ponds more than 100 gallons it will require MUCH MORE surface area than the few pads in a “waterfall filter” or what’s “naturally” produced on the sides of the pond, etc. As an added bonus a good biological filter will double as a mechanical filter as well, straining out organics to help keep your pond water clear.
Rocks lining a streambed are a type of biological filter that we use to augment a filtering system – not take the place of one. Pond water continually runs down the stream, washing the rocks, creating healthy dissolved oxygen and building up good bacteria. Over a period of time, organics will lodge between the rocks and accumulate, mandating occasional cleaning. It’s much easier to clean a stream filled with rocks than the bottom of a pond. You can dislodge the organics by removing the rocks or gravel and vacuum the streambed with a wet-dry vac.
If a pond has no fish you could get by with only a “natural” type of filtering but we all tend to grossly overstock our ponds. Mother Nature would never stock her lakes as heavily as we do our backyard ornamental ponds. That’s another reason our manmade ponds cannot qualify as a natural body of water. We stuff as many as 20 (or more) goldfish and koi into 500 gallons of water. You won’t find that many fish in 10,000 gallons of lake water!
I can understand why a person may opt “not to have fish”. It does require good filtration and overall added cost. Even if you don’t place a good biological filter on your pond when you first construct it you will be thanking yourself for including it in your future plans. If you purchase that first fish, go ahead and start researching a proper filter. If you think that you will never – never – never put a fish in your water garden you need to seriously think about it again. My experience has been that 99.9% of the folks who say they will never – never – never put fish into their ponds actually DO – and they fall in love with them to boot. They name them and the kids enjoy feeding them.
A pond that is built with the old-school-my-pond-is-natural-because-it-uses-natural--filtration-method is a time-bomb ticking away just choosing a time to kill fish. It may take a couple of years of muck building up and fish multiplying and growing beyond the “natural filtering” ability but it will happen eventually. The kids run out to feed the fish and the fish are all belly up or they die off mysteriously one by one. That’s when we get the call.
“All my fish died. What happened?”
“Have you checked for ammonia or nitrites?”
“No.”
We test the water and find high ammonia.
“Do you have a biological filter on this pond?”
“Yes, we have a side-skimmer with the filter in the waterfall.”
That’s when we inform you that you do NOT have a proper biological filter.
It gets right back to that bad information you received when you were searching the internet for pond construction. Unfortunately many landscapers subscribe to that same “natural” theory and promote the installation of the only system they know which is the side-skimmer system. So if you trusted one of those landscapers to put in the right system then you’ve gotten bit.
There is hope for existing ponds that are built the “natural” way. Invest in a REAL biological filter. Remove the rocks from the bottom and start pulling the water from the deepest part of the pond. The worse that can happen is that your liner builds a healthy coat of green and your water stays healthy for the fish. After all, isn’t better to invest in a good filter than to throw money away on fish that die?
Whether you are constructing a pond now or wanting to improve the pond you have now the following articles (filled with good information) should help.
The Doc's Dream System -- A Construction Guide to Backyard Ponds
Choose Your Pond Builder Wisely
Bond Between Pond Builder & Buyer
Landscaper's Dream - Pond Owner's Nightmare
Old School of Pond Construction & Design
Pond Planning Pitfalls & Problems
Turn Your Pond into a Cess Pool - In One Easy Lesson!
Healthy Ponds Have Healthy Bacteria - How to Keep Your Biological Filtration in Shape
Water Parameters - Why those tests are important
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