The Search for Clean Pond Water

A pond can be a dynamic ecosystem providing a window to some of nature’s intimate moments: the mating rituals of native shiners, a turtle hunting crayfish, a dragonfly larvae capturing fry for food, a green Molly discovering that not all ghost shrimps are intimidated by a fish…and will attack. Crystal clear, clean pond water plays a vital role in the degree of enjoyment you can derive from your pond.

The Almost Perfect Pond Habitat

My last project was a four-level pond with an eye for keeping various incompatible species of plants and animals living in a small piece of the backyard. The Critters included two species of water turtles, a bullfrog, ten species of fish, freshwater clams, crayfish, ghost shrimps and two species of salamanders; the greenery, thirty-two or so species of water loving plants. As an oasis in the desert, this habitat attracted a menagerie of birds year throughout the year.

An ambitious design: standing four feet off the ground, its first level a shallow pond for miniature Lilies, decanting nine hundred gallons of water per hour down a sheer drop of lava rock to the ‘Cattail lake’ that is the main pond. Roughly kidney shaped, this pond is about two feet deep and holds around 2500 gallons of water. One of its side walls was designed to appeal as an inviting bench to encourage a more intimate observation of the pulse of life below the surface. Taller water plants such as Spike Rush, Canna, Horsetail, Pickerel, Thalia, Arrowhead and, of course, Cattail, provide ample shelter for the smaller and slower denizens to avoid the predators.

From this ‘lake’, water decants onto the third pond level over a brick miniature version of the Niagara Falls Horseshoe, providing soothing notes to mellow the brassy cacophony of the first waterfall.

This third level is the foot-deep 1500 gallon Water Garden Habitat. It is a shallow quasi-rectangle favored by our two shy Map turtles, the bullfrog, shrimp, a few crayfish and most of the native fish. It is also home to plant species that thrive as floating mats: Water Poppy, Snowflake, water Hyacinth and Primrose. From early Spring and through the Fall these plants are in bloom, a canvas of bright colors and delicate scents…a true Water Garden.

Water careens out of this pond through a brick wide gap on lip of its far wall, flowing to the fourth and last level of the habitat: a foot-deep trench containing the River and Bog habitats.

The Bog covers a third of the area to the right of the gap, and is home to a variety of bog Lilies, rushes, watercress, local riparian plants and our Sycamore and Tamarix trees. It is also the official home of our Soft Shell turtles, Jack and Pancake. The ten feet long River, flows to the left of the break and is home to most crayfish, clams and native fish that love strong water currents. At the end of the river the water is sucked by the half hp pool pump and send on its way to the cartridge filter then returns it to the first high pond.

Designing a Trouble-free Pond

Any pond over three hundred gallons moves the owner from the realm of water filtration to that of Water Management. Maintaining crystal clear, clean water in a pond requires: (1) a submersible pump capable of cycling the entire volume of the pond every three hours, (2) a cartridge filter sized for a swim pool with a volume at least four times that of your pond, (3) a surface skimmer inlet for every 20 square feet of water surface (but preferably never less than two) with easily–removed 1/8-3/16″ mesh baskets for debris collection, (4) a main drain intake at its lowest depth (also with a mesh basket), (5) a passive filtering ‘riparian/bog zone’ designed to work like undergravel filters work in fishtanks. Plumbing requirements include return ‘jets’ to channel floating debris towards the skimmers and at least one waterfall to oxygenate the water.

In this pond, I originally intended to replace the skimmers by installing a wire mesh shelf under each waterfall for leaf and debris collection. The aggressive water decanting at the waterfalls and the strong currents resulting, the large Bog zone and the oversized cartridge filter belayed the need, however. Skipping skimmers saved a good deal of work, time and materials.

Trouble In Paradise

The filtering system developed mechanical problems during one of my months-long stints as an over the road truck driver. Attempts to repair it somehow lead to plumbing issues that made it necessary to shut the system down. We now had a mature habitat: the Sycamore and Tamarix trees in the Bog/River area plus the Sumac next to the water garden now topped over ten feet and contributed as much debris in the form of dead leaves as the two Olive trees over the Koi pond. The lack of strong current and the accumulation of debris accelerated the propagation of a number of the more invasive water garden plants while killing a number of other species.

The Water Garden section was beyond sister’s ability to handle, soon turning into an unsightly breeding ground for mosquitoes and was drained. It became the base for an aviary. The top pond, having the smaller capacity, simply could not be kept free of leaves and so was also drained and turned into a micro greenhouse herb garden.

The River/Bog component was easily enough managed by using a small immersible pump at the intake end and using a half-inch hose to carry the water right to the bog, letting the sandy earth filter the water through percolation. The large Cattail ‘lake’ housing the Koi was the challenge. Draining a 2500 gallons is the kind of waste that goes against the grain for one living in the desert. So, how to clean this swamp?

Clean Pond Water on a Budget

The Bird Aviary had become a necessary feature by the time I was able to return home, so a new strategy for filtration was called for. Incorporating basic water management features would require extensive replumbing and reconstruction, so a new, low cost, strategy was called for. I used $49 dollar immersible pump from Harbor Freight (500 gallons per hour), a discarded above ground pool cartridge filter from a thrift store (the actual cartridge is a cylinder 5″ in diameter by 8″ high), some garden hose and half of a log from a desert dried Juniper tree.

I placed the pump at one corner of the pond and built a skimmer using bricks to form a chimney around the pump reaching just past the surface of the water, a brick removed from the top lip so the water could stream into the chimney as the pump did its job. I removed the electrical components from the kiddy pool filter, sealed the base (using a piece of plexiglass cut to shape and glued with fishtank silicone), and hooked a hose from the new pump to the filter cartridge inlet. Another length of hose was attached to the filter outlet and run to the log, now laying on top of the side of the pond. The log provides the riverbed for a natural waterfall and a good medium for water-loving plants to grow, naturalizing in less than a season and providing passive filtering by trapping silt.

The first day, the small cartridge in the filter required hourly cleanings and did not seem to be making any progress towards water clarity. A day later the filter would take three or four hours before the outflow stream slowed considerably, which was my cue to hose down the cartridge element. By now, there was a perceptible difference in water clarity. As the days passed, the periods between required cartridge cleanings continued to lengthen and the bottom of the pond –24″ below the surface– was visible.

In five days there was no haze in the water: as close to perfect clarity as I could hope for.