Converting a Chlorine Pool to a Natural Swimming Pool

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Image Credit: Oscar Cariss

On the vanguard of swimming pool technology, you'll find several alternatives to a chlorine pool, including one with a generator that can make chlorine from saltwater and a pool that relies on ultraviolet light to purify water, but a natural swimming pool is perhaps the most radical departure from a traditional chlorinated pool. With its back-to-nature filtration system, a natural swimming pool can teach you that a balanced ecosystem is a better way to make clear water than by using sanitizing chemicals.

Perhaps you have an existing pool that has a conventional chlorine-based filtration system, and you want to convert it to a natural swimming pool. While it's a great idea, you need to know a few things first because this type of conversion isn't always practical. Depending on the conversion method, you may need extra space in your yard, and your living pool may have trouble surviving if you live in a climate with extreme temperatures. If the conversion does turn out to be feasible and you go ahead with it, expect your approach to pool maintenance to change considerably.

What Makes a Natural Swimming Pool Different?

Your existing swimming pool has a circulation pump that cycles water through a filtration system that consists of skimmers to remove large debris and a main filter to handle most of the microbes. The filter media may be sand, diatomaceous earth (DE) or some other inorganic material, and to keep the pool clean, you have to change the filter media periodically. A DE or sand filter doesn't kill all the microbes in the water, which is why you need a sanitizer, like chlorine, which may be introduced directly or extracted from saltwater by an electrolytic chlorine generator.

A natural swimming pool also needs a filtration system, but instead of chlorine, it relies on an aquatic garden, called the regeneration zone, which is connected to the swimming area to purify the water. The garden doesn't control microbes, such as algae and bacteria, by attacking and killing them; instead, it uses up the nutrients the pathogens need. Rather than being full of irritating chemicals and dead microbes, the water in a well-designed natural swimming pond is as alive as the water in a mountain stream.

The key to maintaining a biological filter system is continuous water circulation, and to achieve this in a traditional pool conversion, you'll need to modify the circulation system to direct water gently through the plants in the regeneration zone rather than sucking it through a filter. The method you use to do this and the equipment you need depends on how you configure the pool, and there is more than one possibility. You'll also need to rethink the filtration system, and after establishing the garden, you'll have to maintain it.

A Standard Natural Pool Conversion

Companies like Biotop and BioPoolTech manufacture and sell equipment that allows you to convert your existing pool to a living pool, although it should be noted that the swimming area will be reduced to half because the regeneration zone requires 50 percent of the pool's surface area. The equipment supplied by Biotop includes a submersible circulation pump, a special skimmer with a fine mesh filter, an additional bio filter and a carbonator that feeds carbon dioxide into the water to feed the plants. You divide the pool in half using a partition, which you can also purchase from Biotop if you don't want to build one, and you place the pump and filters in underground compartments in the garden end of the pool.

To prevent the swimming area from being overgrown with algae, it should be 5 to 6 feet deep, so when you're converting a standard pool to a natural swimming pool, you'll want the swimming area in the deep end, and you'll want to fill the shallow end with soil and other growing media for the plants. This isn't the only way to design a natural pool, but it's the one that works best with Biotop's equipment. If you want to use different equipment for the circulation and filtration system, you can design your pool differently.

More Natural Swimming Pool Designs

If the idea of using half of your pool for the regeneration zone (and therefore losing half your swimming space) isn't appealing, the answer may lie in slightly expanding the area of your backyard pool. The larger the body of water a natural swimming pool occupies, the more successful the plants will be in controlling algae, so if you have lots of space in your yard, you may want to consider enclosing the pool with a 2- or 3-foot retaining wall and flooding an area around the pool to accommodate the plants for the regeneration zone. In order to make this design work, you'll need to lay down a waterproof liner around the pool. You may need more than one submersible pump to keep the water circulating, and you'll also need skimmers and filters to control debris.

You don't need as much extra space in the yard to enclose an existing pool with a water garden as you might think, however. The surface area of a midsize 15 x 30-foot in-ground pool is 450 square feet, and you can double this area by constructing a pool perimeter only 4 feet away from the sides of the existing pool to create a shallow zone for the plants. As long as they hold water, the walls for the new pool enclosure don't have to be straight; they can curve along garden beds or walkways.

Another type of natural pool design calls for a standard pool curb on one side and one end to form the swimming area and a manufactured shoreline on the other side and end for the plants. This design makes it easy to identify the swimming area, and it makes your existing pool look more like a pond and less like a water-filled concrete hole in the ground, but because of the reduced swimming area, it isn't an ideal pool in which to swim laps. You do this conversion by enclosing the swimming area with a submerged wall and filling in the garden area with enough soil to cover the pool curb and blend into the surrounding landscape.

You Can't Always Make the Conversion

If you have a smaller pool and no room to expand, you might want to consider alternatives to a natural swimming pool conversion. The minimum recommended water surface area to avoid having the swimming area overrun with algae is 500 square feet, so a 10 x 20-foot pool would be too small unless you can build a bigger pool around it for the water garden. Converting a 10 x 20-foot pool would provide only a 5 x 10-foot swimming area, which is more of a soaking pool than a swimming pool.

Climate is another factor that can work against a natural swimming pool conversion. Unlike a conventional pool, you can't drain a natural pool during the winter because it's full of plants, and if the pool liner is concrete, it could crack when the pool water freezes over. A pool in full sun in a region that gets very hot summers is not a good candidate for conversion either because of the difficulty in controlling algae. In climates that aren't suitable for natural pools, it usually makes more sense to convert your chlorine pool to a saltwater pool. You'll save money because a saltwater conversion is much less expensive than converting to a natural swimming pool.


Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in 2010. He worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at

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