What are the differences between a formal koi pond and a natural ecosystem koi pond? Formal koi ponds are very aesthetically pleasing to a lot of people....clean lines...symmetrical shapes...very modern looking... goes really well with Frank Loyd Wright architecture 😁 They are, however, about twice as much to build and not as easy to maintain simply because they lack a significant amount of surface area for beneficial bacteria to grow. They require more expensive filtration and UV clarification to keep the algae blooms at bay.Natural ecosystem ponds can usually be built in a day or two. The entire surface below water acts as a giant filter... the boulders and gravel provide plenty of space for the beneficial bacteria that complete the water cycle to flourish. The algae that grows on the surface on the rocks also provides a food source for the koi, and actually boosts their immune system. That means maintenance @is kept to a minimum...because water gardens are meant to be relaxing... not more work.