It is possible to pair concrete liners with a flexible liner like AquaArmor, and there are a few good reasons why you might want to do this. Concrete alone is harder to clean than a flexible liner, and it can promote water loss through seepage via micro-cracks in the concrete. That’s why you’d want to place a geomembrane over a concrete liner—to prevent that seepage and make it easier to clean your pond after growth cycles.
As to whether you need a concrete liner at all, that depends. In many cases, you can simply use a flexible liner without the concrete. However, if you’re building the pond over weak soil that is prone to shifting, or building a high volume pond, concrete can add some reinforcement that prevents excessive shifting over time. The concrete may crack as soil around it shifts, but the flexible liner will prevent those cracks from turning into leaks. For that matter, flexible liners are also an easy way to press a leaking concrete lined pond back into service. If the pond is cracked, rather than expensive excavation and repairs plus the risk of future cracks in the same place, you can simply cover the concrete with a flexible liner.
