I’ve read all of the literature and tried most of the different styles, sizes and shapes of biofalls filters and skimmer boxes. We installed them ourselves for many years. The first one in about 1999 and the last one about ten years later. We started our career in pond building in this way, because this is what was being taught at the time. Aquascape Designs started the water garden and pond kit industry in the 90’s and many companies have followed suite, creating a myriad of differently shape, styled and sized boxes of all sorts. In the end, after years of trying in earnest to make these things work, and trying to understand pond balance, we finally realized that we were doing our clients a disservice by installing these systems. These biofalls box, skimmer box, and canister filter systems were all just ways to simplify installation.
The problem is, by simplifying installation, we were greatly complicating our client’s pond system. Clients don’t want complication and more maintenance around the house, they want a beautiful, easy to care for eco-system pond. Below are the details of what we have learned and how we made the change to our simple system. A system that we have been installing and perfecting for over fifteen years. These box systems pale in comparison to upflow wetland filters and wet well intakes. This comparison dives into design, functionality, maintenance, cost-effectiveness, ecological integration, and long-term performance, arguing that upflow wetland filters and wet well intakes are a far superior choice.
Introduction: The Filtration Face-Off
Pond filtration systems are the backbone of maintaining clear, healthy water in backyard ponds, koi habitats, and decorative water features. Skimmer boxes, biofalls boxes, canister filters, upflow wetland filters and wet well intakes are common approaches, each with its own philosophy. Skimmers aim to mechanically remove surface debris, biofalls and canisters focus on biological filtration through cascading water and filter material, and upflow wetland filters leverage natural processes in a gravity-defying design. While skimmers and biofalls dominate the market due to aggressive marketing and ease of installation, they often fall short of the robust, low-maintenance efficiency offered by upflow wetland filters. Here’s why skimmer boxes and biofalls boxes are inferior—and why upflow wetlands deserve more attention.
Skimmer Boxes: A Flawed Mechanical Fix
Skimmer boxes are designed to skim floating debris—leaves, twigs, pollen, and dust—from a pond’s surface before it sinks and decomposes. They typically consist of a weir door, a debris basket or net, and a pump that pulls water through to a downstream filter or discharge. This system originated in swimming pools, where it makes much more sense due to the extreme cleanliness of swimming pool water. At first glance, applying skimmers to ponds seems practical, but dig a bit deeper into their design and application, and the cracks appear.
Limited Capacity and Clogging
Most skimmer boxes have undersized baskets or nets that fill up quickly, especially in ponds near deciduous trees or during seasonal leaf drop. Even the largest boxes get choked up and starve your pump of water ensuring a short pump life. A clogged basket restricts water flow, overworks the pump, and allows debris to spill back into the pond—essentially negating the skimmer’s purpose. The small sized weir also makes skimmer boxes very sensitive to water level, once again starving your pump of water with even the slightest amount of system water loss. In contrast, upflow wetland filters and wet well intakes don’t rely on a single choke point like a basket. Water moves through layers of gravel, plants, and media, distributing debris across a larger surface area. This design handles higher debris loads without clogging, as organic matter gets trapped and broken down naturally by microbes and plant roots.
Fragile Construction
Skimmers, are plastic formed boxes with pivoting mechanical weir doors, plastic filter racks and plastic or cloth leaf baskets. They are mechanically fastened to the rubber liner using silicone and screws or bolts which are prone to failure due to corrosion and/or boxes shifting and heaving out of the ground in winter. Because your pump is in a shallow plastic box with a plastic lid any pump noise will be amplified and will take away from the serenity of your pond and waterfall. Also, because the pump is in a shallow plastic box, you will need to remove it before the water freezes or risk cracked pipes and maybe a damaged pump. The boxes warp and tilt over time and nothing fits correctly after the first couple of years. Wet well intakes, on the other hand are much harder to install, but there are no perforations in the rubber pond liner to leak, no filters or baskets to clean, no racks to break and your pump is so deep under water that you don’t need to remove it in the winter and you can’t hear it at all. Both intakes and wetland filters are built in a very simple manner, relying on pond rubber, piping rock and river gravel to filter your water and protect your pump with no mechanical seals or parts to fail.
Installation and Maintenance Woes
Installing a skimmer requires precise leveling and sealing to prevent leaks, a process that’s labor-intensive and prone to error. Once installed, maintenance is relentless: emptying baskets, unclogging pumps, and replacing worn parts. Neglect it, and the skimmer becomes a stagnant, algae-filled liability. Upflow wetlands and wet well intakes, while requiring upfront planning (e.g., sizing the bed and plumbing), are low-maintenance once established. Plants and microbes do the heavy lifting, reducing the need for constant human intervention.
Narrow Scope
Skimmers only address surface debris, leaving dissolved waste, ammonia, and submerged muck untouched. They’re a one-trick pony, requiring additional filters to tackle biological or chemical issues. Upflow wetland filters and wet well intakes, however, are holistic. Water is filtered and cleaned through rock, gravel and plant roots, where mechanical, biological, and chemical filtration occur simultaneously—trapping debris, breaking down waste, and absorbing nutrients.
Biofalls Boxes: A Biological Bust
Biofalls boxes are marketed as biological powerhouses, using a waterfall-like structure to aerate water and host bacteria that process organic waste. Water flows over mats, bags of lava rock, or proprietary media, theoretically creating a thriving microbial colony. In practice, biofalls often fail to live up to their billing, especially when stacked against upflow wetland filters.
Inadequate Biological Capacity
The biofalls concept hinges on sufficient surface area for bacteria to grow, but most units are too small for ponds with significant fish loads, like koi or goldfish. A 500-gallon pond with a dozen koi produces far more ammonia than a typical biofalls can handle, leading to water quality crashes. On larger ponds, even installing multiples of the largest boxes proves to be inadequate. Once again, like the skimmer boxes, these boxes have mechanical parts to fail and they tend to heave, tilt and deform over time. The media—often cramped into a compact box—clogs with sludge, reducing oxygen and killing bacteria. Upflow wetland filters scale better: their expansive gravel beds and plant roots offer vastly more surface area for microbial growth, easily handling higher bioloads and water flow without choking.
Maintenance Nightmares
Cleaning a biofalls is a slog. You’re left wrestling with slimy mats or rocks, often spilling muck back into the pond during the process. Media replacement is frequent and costly, especially with branded systems locking you into proprietary parts. Upflow wetlands sidestep this entirely. Debris settles into the gravel, where it’s broken down naturally, and plants uptake excess nutrients. Maintenance is minimal—occasional trimming or thinning of plants—versus the hands-on drudgery of biofalls.
Temperature and Aesthetic Trade-Offs
Biofalls’ cascading water aerates well but cools ponds excessively in colder climates, slowing fish metabolism and growth. The artificial plastic box and waterfall look also clashes with natural pond designs. Upflow wetlands maintain stable water temperatures (since flow is subsurface) and blend seamlessly into landscapes, with emergent plants mimicking natural wetlands. They’re both functional and visually harmonious.
Dependency on Upstream Systems
Biofalls need a skimmer or pump to feed them water, tying you to a multi-component system that’s only as strong as its weakest link. If the skimmer clogs or the pump fails, the biofalls starves. Upflow wetlands can be built in numerous ways to minimize the need for pumps and mechanical devices. A rubber liner with no penetrations, a bed of stone and gravel, some piping and a host of aquatic plants is the ultimate filter and the ultimate in simplicity and reliability.
Upflow Wetland Filters and Wet Well Intakes are the Superior Alternative
Wet well intakes hide and protect your pump, eliminate water level and water loss problems and filter your water. Upflow wetland filters turn traditional filtration on its head—literally. Water enters at the bottom of a gravel-filled bed, rises through layers of rock, gravel and plant roots, and exits at the top, feeding back into the pond or stream. This design leverages natural processes in ways skimmers and biofalls can’t even come close to.
Holistic Filtration
Unlike skimmers (mechanical only) or biofalls (biological focus), upflow wetlands excel at all three filtration types. Mechanically, gravel traps debris; biologically, bacteria in the gravel and roots process waste; chemically, plants absorb nitrates and phosphates, preventing algae blooms. This trifecta makes them vastly more effective at maintaining water clarity and ecosystem balance.
Scalability and Adaptability
Wet well intakes and Wetland Filters can be scaled to fit any pond size. A small backyard setup might use a 4×4-foot bed, while a large koi pond could span 10×10 feet or more. Their capacity grows with their footprint, unlike skimmers and biofalls, which hit diminishing returns beyond their fixed designs. Wetlands also adapt to fluctuating conditions—more fish, more debris—because plants and microbes self-regulate, a flexibility that skimmers and biofalls lack.
Low Maintenance, High Durability
Once established, upflow wetlands and wet well intakes are nearly self-sustaining. Plants like irises or rushes thrive in the nutrient-rich water, their roots hosting bacteria that break down waste. Gravel beds rarely clog, as flow is upward and debris disperses naturally. Compare that to skimmers’ constant basket-emptying or biofalls’ media scrubbing—wetlands save time and effort. Structurally, they’re tough: no brittle plastics or moving parts to fail, just liners, rocks, and plants that endure for years. Your wet well intake will likely only need to be opened up when your pump fails, so maybe once every five to eight years?
Cost-Effectiveness
Skimmers and biofalls carry high upfront costs—$200-$1200 each, plus pumps and plumbing—and ongoing expenses for parts and media, but their real cost is the hours and hours of unnecessary maintenance and frustration that they will bring you over the entire life of your pond. Upflow wetlands and wet well intakes are more difficult to install, but they are made with all simple, super durable parts and the emotional stress and strain that they will save you over the years will prove to be invaluable. If you want the best filtration possible, with minimal headaches, the upflow wetland and wet well intake system can’t be beat.
Ecological Integration
Wetlands mimic nature, supporting biodiversity with plants, insects, and even small wildlife. They reduce pond nutrient loads, curbing algae without chemicals. Skimmers and biofalls, by contrast, are sterile, mechanical intrusions that contribute little to the ecosystem and often require additional interventions (e.g., algaecides) when they falter.
Aesthetic and Functional Harmony
A well-designed upflow wetland looks like a natural bog or marsh, enhancing a pond’s beauty while filtering water. Skimmers hide awkwardly at the edge, and biofalls’ plastic waterfalls often feel forced. Wetlands deliver both form and function, a balance the others can’t achieve.
The Verdict: Skimmers and Biofalls Fall Short
Skimmer boxes and biofalls boxes aren’t useless—they have their niches. Skimmers can help in tiny, debris-heavy ponds with minimal fish, and biofalls might suit tiny water features where space limitations trump efficiency. But for most pond owners, especially those with larger systems or serious fishkeeping goals, they’re greatly inferior to wet well intakes and upflow wetland filters.
Skimmers are fragile, one-dimensional, and high-maintenance, failing to address the full spectrum of pond challenges. Biofalls promise biological filtration but deliver underwhelming capacity, messy upkeep, and dependency on other systems. Upflow wetlands, by contrast, offer a robust, scalable, low-maintenance solution that integrates mechanical, biological, and chemical filtration into one natural package. They’re cheaper long-term, more durable, and ecologically sound, making them the gold standard for serious pond management.
In the end, skimmers and biofalls feel like shortcuts—marketed as fixes but riddled with compromises. Upflow wetland filters embrace nature’s complexity, turning it into a strength that leaves the competition in the dust. For anyone serious about a thriving pond, the choice is clear: wetlands and wet wells win, hands down.