Pond Liners: the Hole Story

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Sometimes I get calls from people who have purchased a new home with an old pond that has a big problem. The number one complaint is that it will not hold water; second is that the water is green; third is that the rock work is ugly – an eyesore!

At that point I ask if their waterfall and pond are constructed with a pond liner, and they are surprised that I knew that. However, eighty percent of all these types of calls pertain to a liner pond and waterfall. We have replaced over $80,000 worth of defective liner ponds. One customer in Rancho Bernardo, California, had spent $14,000 to have a koi pond and waterfall built by a large and well respected local pond liner supply company. They complained of needing to add water daily since the liner pond was constructed over a year ago.

The pond liner installer’s response was that the loss of water was from evaporation. The liner pond was fitted with a manual auto fill system and they discovered the solenoid was turning on every 15 minutes to replenish the loss. In addition to the annoying water loss, they could not enjoy their fish for half the year because of murky green foul-smelling water. They reported the pond liner company came out dozens of times dumping various concoctions in the pond with a promise of startling results. The results were startling all right – our client sued the pond liner store and contracted with us.

The first thing I discovered was that the volume of the liner pond was 8,000 gallons and the waterfall pump was only 1,000 gallons per hour. It was taking eight hours to run the total pond volume through the filter. Secondly, the filter was rated for a 2,000 gallon pond, not 8,000. (Filters are usually overrated by their manufacturers as it is.) Third, the ultraviolet light was also rated for a 2,000 gallon pond, making it only one-quarter effective (according to its ratings) at controlling suspended algae growth. Fourth, because the pump was only 1,000 gallons per hour, it was not strong enough to properly backwash the filter, which requires four times the flow to be back-flushed properly.

Consequently, the filter was overloaded with rotting waste material that was contributing to additional pollution of the liner pond. The fifth defect in design was caused by the pond’s large surface area, which was surrounded by several deciduous trees that were dropping their leaves into the liner pond. Needless to say, there was no skimmer installed. So all this debris ended up rotting on the bottom of the pond, contributing to the nitrate and ammonia overload.

The sixth discovery was that the suction drain on the bottom was at the same end of the liner pond as the waterfall. Consequently, the water was only circulating between the water returning to the pond and the water leaving it (from waterfall to drain). Half the liner pond was not circulating properly and was stagnating because the nitrifying bacteria were not receiving adequate oxygen to do their job of breaking down the nitrites.


We were asked to assess the condition of the liner pond and determine the cost to correct the problems found. We turned off the waterfall in the liner to test the evaporation theory and discovered (with the falls turned off) that the pond was losing 25 to 30 gallons per day, or 750 gallons per month! Installing a larger pump filter and UV was not going to solve all their problems.

I suggested that since a reputable pond builder and store owner was involved, he should get a second opinion. He was confident that, with our reputation of 22 years and 1,800 ponds under our belt (at that time), we knew what we were doing.

After finding a temporary home for the fish, we drained the liner pond and quickly made two discoveries. As the water was being pumped out of the pond, there was a small waterfall developing from the water that poured back through a hole in the liner created from a tree root. Also, water was leaking back through a loose seal around the bottom drain as fast as we could pump it out. (This continued for some time, revealing there were hundreds of gallons of water being stored in the sandy soil surrounding the perimeter of the liner pond due to the ongoing leaks.)

We offered to repair the faulty drain and patch the punctured liner and refill it, but the owner insisted we do it right, using rebar plus 3500 PSI concrete and skimmer. Unfortunately, not one single item in the entire system could be reused in

the new construction. Even the PVC piping had to be scrapped since it was undersized for the pump.

In the final analysis, because this project was not thought out or designed properly, the initial $14,000 spent was entirely wasted. Replacing everything and installing it correctly cost the customer $17,000. The new pond was constructed of 3/8” and ½” rebar, 10” on center with 4 ½” of 3500 PSI concrete and fiber mix added. The ugly fiberglass waterfall was removed and replaced with a natural looking waterfall constructed of concrete real granite rock.

A skimmer was installed on the opposite side of the pond from the waterfall. The bottom suction drains (two anti-vortex drains in series to prevent turtles or fish from getting ****** against the drain) were placed on the opposite side of the pond from the waterfall to maximize circulation.

Next, a Venturi valve was installed to add additional oxygen and create a circular current in the pond. This delivers oxygenated water to all areas. A 6000-gallon biofilter was installed with two 180-watt ultraviolet lights. The high efficiency filter pump, which runs 24 hours a day, and is rated at 4,800 gallons per hour.

We installed a second pump of the same rating to allow for twice the flow volume off the waterfall on demand. It is also operated by a timer that comes on twice a day for one hour. This keeps sediment stirred up in the waterfalls and pond to aid the filter in removing it. The skimmer now removes 90 percent of all debris falling into the pond before it can become waterlogged and sink to the bottom.

The electronic water level control we installed in the previous pond at the owner’s request was the only item that was reused in the new system. It is designed to add water to the pond automatically as needed due to normal water loss through evaporation and wicking around bog planters into adjacent soil.

This story has been repeated dozens of times over the past few years. Fortunately, most of them were on a much smaller scale.

Most of our business is word of mouth, so I imagine there are many people who, not knowing whom to call, simply gave up and turned their water feature into a rock garden. Think twice before investing too much money into a liner pond. Ask the contractor specific questions about the precautions he takes against leaks caused by roots and critters. Also, get several bids on concrete and rebar constructed ponds, they usually only cost 20% more and can be expected to last for decades.

My last word of advice, be patient, take your time and thoroughly investigate the contractor and his claims.

An ounce of prevention…

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