Fish and plant safety are one of the main requirements for an aquaculture geomembrane. However, don’t fall for the misconception that it’s all you need to look for in a product. While choosing a liner based on that factor alone may work okay for a small backyard pond, it leads to unnecessary costs and installation issues on a larger scale. A profitable aquaculture business begins with careful selection of each material. If you’re new to comparing geomembranes, you may not know how to compare them or what features actually matter. Try these tips for selecting the right geomembrane for any aquaponics, hydroponics, or aquaculture project.
Choosing the right polymer material is the single most important selection to make aside from checking for fish and food safety. The polymer or combination of polymers used in the geomembrane determines everything from its UV resistant to its overall strength. The wrong polymer will have a high chance of leaching unwanted chemicals into the water unless you choose a tested and rated product. Other polymers are safer and more likely to achieve the correct NSF rating. Compare your options below to find the right fit for your aquaculture design.
PVC stands for polyvinyl chloride, and this material was the most widely used option for lining ponds of all kinds for many years. It’s far from the best option today thanks to improvements in other materials. PVC is not as strong as most polyethylene mixtures, especially when compared to reinforced polyethylene (RPE). It is thinner and more flexible than other highly durable liners like EPDM, but it often fails to pass the fish and plant safety tests to qualify it for use in aquaculture. PVC also tends to offer a shorter lifespan than other materials, even when buried.
High density polyethylene (HDPE) is a relatively stiff polymer, but it’s still flexible enough to use as a geomembrane. It’s tougher than PVC and much more tear resistant, yet cold and freezing temperatures cause it to become brittle and crack. Most HDPE liners are somewhat fish or plant safe, but not all offer this certification. All polyethylene-based liners, including HDPE, offer good UV and chemical resistance. HDPE is a better choice than PVC or EPDM, but it’s still not as good as RPE for all aquaculture purposes.
Low density polyethylene (LDPE) offers a lot of the same benefits of HDPE in a more flexible package. Unfortunately, that flexibility comes at the cost of some strength and tear resistance. Chemical resistance also varies in this range. While aquaculture systems don’t involve a lot of caustic or corrosive chemicals, the nutrients and byproducts in the water can still shorten the lifespan of these liners. RPE is a better choice since it includes LDPE for its flexibility but improves on its less than positive features.
EPDM (ethylene propylene diene monomer) is a type of rubber that was one of the first materials used for pond liners. Sheets of this material are thick and heavy, making them expensive to ship and difficult to install. The stiffness of the material keeps it from conforming to curves and sharp corners in ponds and raceways, but it also helps the liner resist punctures and tree roots. It also suffers from a short lifespan, especially when exposed to the sun and its UV rays. Many EPDM sheets and liquid coatings are designed for roofs and not for fish and plant use. Steer clear of EPDM for any hobby or commercial aquaculture project.
Chlorosulfonated polyethylene, or CSPE, is another option for creating durable geomembranes. This material is primarily known for its excellent chemical resistance. It’s widely used in mining and industrial holding ponds where acids and caustic solutions would eat away at other materials in mere months. That’s simply not a feature you need in any normal aquaculture situation. CSPE is only rarely available in a certified fish and food safe formulation as well. It’s not generally a good choice for most aquaculture projects, so avoid it unless it’s your only option.
Reinforced polyethylene (RPE) is the best choice for almost all aquaculture systems. Whether you’re building above-ground or below, this flexible yet durable material is ideal for keeping the water in. It combines the best features of both HDPE and LDPE while canceling out the negatives of either. The reinforced design ensures that small rocks and roots in the soil won’t cause the material to rip. Reinforced materials are also much easier to install than non-reinforced polymers. The reinforcement grid encourages the material to spread out and lay flat against the surface, reducing the work necessary to deal with small folds and wrinkles that turn into leaks later. RPE is available in both small sizes and huge custom commercial fabrications, making it a good choice for hobbyists and commercial operators alike.
How to Tell if a Product is Food and Fish Safe
Don’t just rely on claims made by the marketing materials of various geomembrane and liner manufacturers. The National Sanitation Foundation (NSF) is the place to turn for reliable testing to verify a product is truly safe for food and fish use. Thankfully, you don’t have to pay for or submit this testing yourself. Manufacturers that want to prove their products are safe will happily seek out this certification on their own. Look for a NSF 61 rating or higher for both fish and food use. While ornamental fish can live in lower rated NSF liners, edible fish definitely need a NSF 61 rating from their liner. BTL Liner’s AquaArmor is a great example of an RPE product that meets these requirements
Do You Need a Potable Water Liner?
To ensure you’ve reached the highest standard of water safety for your fish and plants, consider choosing a liner that is rated for potable water use. This means that the water stored in the liner would be safe to drink, as long as all other safe practices are followed. You won’t have to worry about any chemicals leaching out of these liners and harming your fish or being absorbed by your plants. If you do order a liner with NSF or potable water certification, keep the product documentation on hand. You may need to prove the source of the specific materials used if seeking approval from an organic or chemical-free certification agency.
If you plan to install your geomembranes so they’re exposed to light, make sure to choose a liner rated for that kind of use. Even within the same line of products from a single manufacturer, individual liners vary in their UV resistance depending on the formula and the overall thickness. RPE liners tend to offer good UV resistance for exposed installation at all levels of thickness. If you don’t want to spend more for exposure rated liners, consider covering all of the material with a few inches of dirt or sand to protect it from the sun instead.
Using an Underlayment
If you choose RPE as your liner material, you should have minimal site preparations to get your ponds or board trenches ready for installation. However, excessively rocky or uneven soil may still cause damage to these liners during installation and over time. For the best results if the ground looks too rough for a flexible liner, add a geotextile underlayment as a cushion. You’ll experience less tearing and leaking while creating an extra barrier against root penetration from the outside.
The process of shopping for the right aquaculture geomembrane can seem impossible. Don’t let the sheer volume of choices overwhelm you. You can always turn to BTL Liners for help in matching the right liner material to your particular project.