While a liner might be a requirement for any custom made hydroponic tank or raceway, that doesn’t mean you can use any pond liner you can find. Using the wrong material will do more than just increase your budget and risk damage to the equipment. Certain liner materials also pose safety risks when used for food-related purposes. Failing to source a food safe liner could result in health issues if you consume the produce yourself or a lawsuit if you sell it. Make sure you’re choosing a liner that’s both food safe and durable enough for hydroponics with these tips.
What’s Required for Food Safety?
It’s not enough for the manufacturer of a particular pond liner to claim that their product is safe for food uses. Each material can contain chemical additives that soften the material and also leach into the water. When the plants absorb the moisture and nutrients they need, those heavy metals or other contaminants also soak in. Make sure the liners you use for hydroponics are specifically tested for food safety. Look for a certification from a group like the NSF. NSF ratings of 61 or better are recommended for this kind of use. This rating is required for potable water use, so it’s above and beyond what’s required for safe food production. These liners are tested over long periods of time to ensure that the eventual breakdown the material due to UV exposure doesn’t change what’s release into the water.
Flexible vs Rigid Liners
If you’re trying to build a small pond as part of your hydroponics as quickly as possible, you might be tempted to consider a rigid liner. These liners are widely sold at hardware stores, but they’re far from ideal for even the smallest backyard design. Rigid liners are more expensive per square foot or gallon than flexible liners once you compare them, especially if you compare the lifespan of a quality flexible liner to that of the rigid one. It’s also much more work to get the fit exactly right to support the rigid liner. Since the flexible material bends to the shape of the excavation, installation is quick and easy.
Permeability
Aside from the flexibility and texture of the liner, you’ll need to consider its overall permeability. Even some flexible liners are more permeable than you might assume. Permeability refers to how easy or hard it is for water to pass through the material. Few materials in the world are truly 100% impermeable, but many pond liners come more than close enough for hydroponics. Check that a liner is intended to offer a high level of water loss control before choosing it for a pond or tank. Highly impermeable liners like RPE materials reduce seepage to practically nothing while keeping water from soaking in as well.
Comparing Flexible Liner Materials
Once you’ve narrowed down your options for a liner to some kind of flexible polymer, you’re still left with plenty of decisions. Start with a material, then narrow it down to a food safe version, and then choose a specific formulation. Taking a little extra time to find the right liner will pay off as you expand your future hydroponic projects. Here’s the most common materials used for lining ponds and some info on whether they’ll work well for hydroponics or not.
EPDM
Ethylene propylene diene monomer (EPDM) is a form of rubber that’s traditionally used as both a roofing material and pond liner. While it is a thick and somewhat durable material, it’s also not a great choice for any hydroponics projects. The thickness of the material that lends it any strength also results in difficulty in fitting the liner into tight corners. It’s also too likely to leach chemicals into the water and therefore rarely qualifies for food safety ratings. Finally, it’s also hard to install due to the extra weight from its thickness. Don’t confuse roofing liner for pond liner either since it’s definitely not going to be food safe.
PVC
Polyvinyl chloride, better known as PVC, is a thinner liner than EPDM. It offers a medium blend of durability and flexibility, but it’s also the material most likely to contain dangerous chemicals that are water soluble. Most or all of your plumbing for your hydroponics will rely on PVC pipe, but this rigid material is designed for potable water safety. The flexible varieties used for liners is a different story altogether. PVC is susceptible to UV damage, so it’s not a good fit for outdoor and greenhouse hydroponics either. Save the PVC for the plumbing and choose a better material for your pond and trench liners that is more likely to pass food safety certification.
LDPE and HDPE
Both low and high density polyethylene (LDPE and HDPE) make decent choices for hydroponics liner, but neither are the optimal material. Both vary in food safety depending on the precise formulation. UV resistance is relatively high, but both materials are generally too stiff to fit the curves of a small pond or trench. Both types of polyethylene also need to be relatively thick for strength when used alone, resulting in heavy liner that is harder to ship and install. For the best results, look for a reinforced polyethylene (RPE) product that combines both LDPE and HDPE in multiple layers to get the benefits of both.
RPE
Reinforced polyethylene (RPE) is a type of flexible liner that combines LDPE and HDPE. It’s also based around a reinforcement layer that increases the tear and puncture resistance significantly. This material commonly comes in food safety and potable water formulations, including BTL Liners products that are rated NSF 61 or higher. The combination used in RPE is particularly easy to weld, making installation fast and reducing the chance of leaks. To avoid seam sealing altogether, it’s possible to order this material in large custom fabricated sheets for reliable performance. RPE is generally thinner than either LDPE and HDPE on its own since the combination is much stronger without needing as much thickness. The extra flexibility helps this RPE compete with soft PVC liners that aren’t certified for food use.
Will You Need Seam Sealing?
If you order a roll of pre-cut and ready to use pond liner, you’ll most likely need to seal at least one seam. Small backyard ponds are likely easy to cover with a single width, but larger commercial tanks and trenches will eventually need some sealing. Choosing RPE from BTL Liners can eliminate seam sealing even on large projects since custom manufacturing is possible at very large dimensions. Discuss your plans with our design team before determining whether or not you can avoid seam sealing in your hydroponics installation.
Watch Out for pH Effects from Liners
In addition to direct contamination from chemicals leaching into the water from the liner, there is also the concern of pH variation. Some liners that are food and water safe nonetheless raise the pH slightly to create alkaline effects. It’s common for many PVC and EPDM lined ponds to stay around a 7 on the pH scale despite efforts to keep it lower. If you’re planning to grow plants that need a perfectly neutral or slightly acidic solution, stick to RPE to ensure there’s no fight to keep the pH correct. This material won’t react with the water, release anything into it, or change the water’s pH balance over time.
Why Won’t Natural Sealing Materials Work?
Organic and bio-dynamic farmers looking to reduce the use of polymers in their farming systems may desire to use natural pond sealing materials instead. Bentonite clay, vegetable oil based treatments, and similar products are widely available and marketed as easy ways to keep ponds from losing water. However, all of these materials are far too permeable to use in a hydroponics system. The slow and inevitable loss of the nutrient solution into the soil will reduce the efficiency of the system and risk crop loss. Only flexible and impermeable liner materials can guarantee reliable performance.
With this information in mind, choosing a liner for any part of a hydroponics project should be easy now. If you’ve still got questions about liners, contact us here at BTL Liners for help. We’re happy to discuss your plans and guide you to the right product.
