After hearing Paul's podcast and seeing some discussion about natural swimming pools, I am convinced that this is a great way to go as far as having a multi-purpose pool goes.  What I'd like to do is to figure out how to heat one during the winter in Ohio where it can get down to zero and sub-zero temps, but is usually 20-50 during the fall, spring and much of the winter.

I have thought about a kind of greenhouse approach with perhaps fresnel lenses to heat up some burried water basins.  I live behind a hill, so I get some direct sunlight in the early to late afternoons.  I could potentially couple this with a rocket mass heater system.  It would be really nice to double this as a green house for growing things whilst being able to swim year round and harvest fish for food (thinking tilapia + duckweed style?).

Any thoughts on what might work?  I think it's crazy to spend money on a pool that can only be used for a single purpose and only during the summer in our area, so this seems like a nice multip-purpose fit to have diversion and utility.

The main problem I see is that most natural swimming pools don't use fish if I remember correctly.

You are right Shawn, I just looked at the free PDF manual and on page 10 it says:

As well as plants there are other vital allies – the  myriad of micro[organisms that make up the  zooplankton living in every cubic millimetre of pond  water. A lot of the small pond creatures are commonly  called “water fleas”, which is a bit unfair because they  are not fleas and certainly wouldn’t bite. Amongst them  are daphnia. These tiny crustaceans are essential to  promoting clear water by filtering out, and consuming,  suspended particles of algae. We need to look after  them. Incidentally, this is the main reason an Organic  Pool shouldn’t have fish. They eat the daphnia.

Notwithstanding, even sans fish, this would still be a project I would be interested in pursuing.

I completely agree. I look forward to hearing about any updates you have on it.

Can you have a filtration section separate from the fish section, so the Daphnia are safe to do their thing?  I know it means more tanks, but I wonder if keeping the swimming, the fish, and the filtration in separate areas might be the deal, since you need to circulate the water anyway, it could be circulated through a series of tanks.  Some of which could grow edible aquatic plants, or aquaponic grow beds, with a tank for fish, and a tank for swimming.

Well @Tyler, that's a good idea. From what I understand that could dramatically change the chemistry of the water and thus require some additional figuring in terms of filtration as you note. I'm not sure what one could do, but I agree that it would be valuable to do so if possible. Perhaps one would have to use a slower growing or populating fish vs something so prolific like tilapia.

As far as warming goes, the videos from Dan Rojas at GREENPOWERSCIENCE really seem to offer some encouraging results as far as how much heat you could generate from parabolic mirrors and a fresnel lens array...

I think Erica Wisner was building a rocket stove that could be put into a hot tub to heat the hot tub.  Would that work to add heat to your system?  I knew some people  a dozen or so years ago who bought a "conventional" type wood stove that could heat a hot tub.  Seems like there would be an efficient way to use wood heat when needed.  I think the biggest danger in heating water is not to have any closed tanks that can generate pressure when heat is added.

I like the idea. What part of ohio are you in? We're in Seville Ohio.  

If swimming area was higher with glass infinity pool with overflow into next aquaponics pool with fish. Then out to last pool of natural filtration that could also water a garden from.  Maybe natural pond part has removable/ roll up awning that would help cool down if needed.  

Also a raised fish cleaning section where fish guts get washed down pvc pipe into an outdoor trench where you grow tomatos.  

Steve Taylor wrote:I like the idea. What part of ohio are you in? We're in Seville Ohio.  

If swimming area was higher with glass infinity pool with overflow into next aquaponics pool with fish. Then out to last pool of natural filtration that could also water a garden from.  Maybe natural pond part has removable/ roll up awning that would help cool down if needed.  

Also a raised fish cleaning section where fish guts get washed down pvc pipe into an outdoor trench where you grow tomatos.  

Interesting ideas there!  My first goal is to insulate and heat it here since I'd like to use it in the winter. In south part of Ohio.

What is your budget?  Do you have access to free wood from forest/ round wood construction?  

Steve Taylor wrote:What is your budget?  Do you have access to free wood from forest/ round wood construction?  

Lots of trees, yes. I have a couple of forests with fairly aged trees available. Budget-wise, note entirely sure. Cheaper the better, but I don't want to skimp and would like to do it right the first time.