When you're investing your money, time, and labor in a pond that will bring you countless hours of pleasure, you want to be sure that both fish and plants will thrive. Setting up a good biofilter, testing your water regularly, and protecting your pond from predators are all obvious steps in that direction. But, a less obvious source of danger is the material used to line your pond.
Plasticizers
Using a liner material that doesn't claim to be "fish and plant safe" may save a few bucks in the initial stages of pond construction, but the long-term consequences of that choice can be both expensive and dispiriting. PVC, for example, is a cheap, readily available material that pond builders often recommend to new enthusiasts wanting to start on the cheap. It comes with a host of disadvantages as a liner, but one characteristic directly affects your fish's health.
In its primary state, PVC tends to be stiff and brittle. The softer, more flexible PVC sold as tarps or pond liners comes from the addition of plasticizers, most often phthalate esters (PAE). Any flexible PVC product, by definition, includes some sort of plasticizer. Still, since there are no labeling requirements for phthalates, it's impossible to confirm whether PAEs are present in any specific sample.
Phthalate esters are readily released into water from numerous consumer products and are one of the world's most prevalent organic pollutants. Studies conducted worldwide continue to link PAEs to health problems in humans, but studies show they also create liver toxicity, cell injury, and death in carp populations. Oxidative stress, metabolic disorders, endocrine disorders, immunosuppression, and genotoxicity in fish populations worldwide have been linked to exposure to PAE and its metabolites.
Some amount of these pollutants is almost certainly present in your pond water. Choosing a liner that is guaranteed to leach even more plasticizers into the water over time is tacit acceptance of both immediate and long-term adverse health effects on your fish.
Additives, Coatings and More
Other off label uses of materials for pond liners include EPDM roofing, which frequently has fire retardants, algaecides, fungicides, and other antimicrobials added even before the material is formed. While these additives are often toxic to fish and plants, many pond owners will seek out the cheaper roofing EPDM and reassure themselves that a good scrubbing with a stiff broom will remove any harmful coatings. Talc, for example, is a dusting material used to keep EPDM from sticking to itself during manufacturing and can be scrubbed off without too much effort. Unfortunately, many of the more toxic additives are fundamentally integrated with the material itself. While they will leach out over months or years, they are impossible to wash off in an afternoon, even if you scrub to the point of damage.
Liner Grades
Polyethylenes as a class are non-toxic to fish and plants, so unless the manufacturer applies some sort of coating, these liners can be assumed to be safe in your pond.
PVC and EPDM are both available in "pond safe" versions, which generally pushes their price point up substantially. The definition of pond safe may be up for question, though. PVC must have a plasticizer to make (and keep) it flexible. Unless the plasticizer is chemically bonded to the material, it will gradually erode and leach into the water, the earth, or wherever it sits. If you're considering a "pond-safe" PVC liner, it's worth investigating whether it meets your risk tolerance -- is there an acceptable phthalate leach rate, or is zero your gold standard?
Many EPDM manufacturers sell both roofing material and pond liners, and most people can't tell the difference between them (or whether there is any). Many pond enthusiasts suspect that the same material serves as both product types, but the pond version has a considerable markup. Given that roofing is the primary market for EPDM, are you willing to bet that the pond-grade material you're buying is significantly different from roofing-grade? You may not see problems for weeks or even months, but leaching is a long-term process. When fish begin to die after five years, who's going to think back to their liner choice?
Potable Water
While polyethylene materials, as a class, are both fish and plant safe, there's no guarantee that coatings or other enhancements haven't been added that create toxic conditions for your pond if you're using the material "off-label." The most reliable guarantee that your pond liner will not leach or do chemical harm to your fish is a potable water designation from the American National Standards Institute. An NSF/ANSI 61 seal indicates the material in question is stable and suitable for containing drinking water for humans. The ANSI designation is a higher performance-based standard, different from the U.S. Food and Drug Administration requirements.
Every material in BTL's AquaArmor line is Certified to NSF/ANSI 61. There is no greater standard for chemical stability and safety. An RPE pond liner from BTL Liners is the most stable, durable, and highest performing liner available on the market.
