Some flexible liners are treated with algaecides, which means you’ll need to choose the right liner for your algae pond. Many liners, even those that are rated as fish or plant safe, will be treated with an algaecide because in most ponds, algae is an undesirable contaminant. Because no one wants a fishing pond or swimming pond that is clogged with algae after only a few years of use, most of these algaecide additives are designed to last. What this means is you’ll need to choose a liner specifically made for algae ponds.
So what liner do you choose? PVC and EPDM liners both usually contain algaecides, and they have plasticizing chemicals that will suppress growth even without the algaecides. With PVC, you’ll also need to keep the liner covered in soil or mud to prevent UV damage from weakening the material, which is not optimal for algae ponds. Liners that are rated as plant safe or fish safe may not work either because most algaecides are actually safe for both fish and more complex plants. You’ll want to look for RPE or HDPE liners like ArmorPro or AquaArmor because these are free of both algaecides and plasticizers. Before purchasing any liner, make sure to double check with the manufacturer to ensure that the liner is suitable for algae production.