Using swimming pools for aquaponics

[GaryD]

Hi,

I regularly get phone calls and email from people who want to use a swimming pool for food production.

While some people suggest that it is not possible (largely because they can't reconcile a swimming pool into the 1:1/2:1 component ratio idea), I believe that a swimming pool would make a wonderful centrepiece for an integrated backyard food production (microponics) system.

While I have some ideas about how this could be done, I'd like to know what you think. How would you make it work?

Gary

[svc]

I would certainly try if I had a swimming pool to play with.
I have heard of this 1:1 1:2 ratio before, it makes no sense to me.
Surely if nitrification is adequate the amount of nutrients used comes down to growing surface area and the plants grown, not the GB volume?
Even if growing space was limited a lightly stocked swimming pool would grow some big happy fish.

[GaryD]

Hi,

Over the past several years, I've encountered a handful of people who have dabbled with the idea of converting a pool for food production purposes. APHQ member Wey2Go grew some trout in his pool.

It's an idea that obviously occurs to quite a few people because we get so many queries about it.

I googled (swimming pool) aquaponics and got some interesting results.

A bloke called Peter Butler has painstakingly chronicled the conversion of his broken swimming pool into an aquaponics system here. Peter's efforts are not for the faint-hearted......there are about 50 YouTube episodes from start to finish. If you fast forward to Episode 50 you get to see what he ended up with.......an aquaponics system.

Geoff Lawton, who runs a permaculture consultancy, describes a pool conversion that he visited on the Gold Coast......here.

I subsequently discovered gardenpool.org who converted a run-down pool in Phoenix, Arizona.....here.

It's fair to say that this is much more the sort of thing that I'd expect from a backyard pool conversion. They have tilapia, chickens, vegetables and herbs all coming out of a greenhouse-covered pool. The chicken poop generates algae that is eaten by the fish which power the plants.

The greenhouse moderates the climate around the pool which is just a large water catchment. The possibilities for other micro-livestock (rabbits, snails, worms, quail, ducks, BSF) and plant (duckweed, salvinia, water hyacinth, azolla) integrations are many.

The mind boggles. Do any of you get excited by this sort of thing?

Gary

[Ravnis]

I would certainly try if I had a swimming pool to play with.
I have heard of this 1:1 1:2 ratio before, it makes no sense to me.

The 1:1 ratio 1:2 ratio was a oversimplification of how much growbed volume was needed to water volume. It is a good starting point and for many it is all that is needed to run a successful aquaponics setup with a low volume of fish to water ratio.

Surely if nitrification is adequate the amount of nutrients used comes down to growing surface area and the plants grown, not the GB volume?
Even if growing space was limited a lightly stocked swimming pool would grow some big happy fish.

You hit the nail on the head from my observations. Sizing the nitrification to the amount of fish, and subsequently the amount of food fed to the fish, is the critical aspect. Size of water only increases the buffer capacity of the system.

A swimming pool is really nothing more than an oversized tank and one problem with that is catching the fish if not kept in cages. I used a cheap above ground pool this year in my greenwater system. Since I didn't have them in cages or other containment, harvesting them was problematic until I just recently harvested them after draining the pool. I would therefore recommend use of some kind of containment/cage system if using a large tank such as a pool.

[GaryD]

Hi Ravnis,

I can see how having fish roaming at large in a swimming pool might be problematic.

Several floating cages would allow you to keep different species (and different age groups) all in the same body of water.....while making it easier to catch them as required. You could also float rafts on the surface of the water without the fish eating the roots.

Gary

[Ravnis]

which leads to another benefit, you could conceivably use the pool as both a fish tank and raft tank at the same time provided there were added methods of : handling solids, aerating the water column and promoting gas exchange, and adding biofitration as needed if the rafts proved to have inadequate surface area.


I rather liked that aquaponics setup you mentioned from Arizona. There greenhouse is basically a pit greenhouse which from what I have read increases temperature stability.

[Cecil]

Harvesting out of swimming pool or similar circular tank isn't necessarily problematic if you have the right equipment to do it. The trick is to build a couple of panels with soft netting that you can rotate from the center point from a closed position to an almost closed position on the other side of the tank to confine the fish for netting.

I'd post a picture but my computer is at the shop and I'm presently using the wife's old laptop. I'll do it later when I get it back if anyone is interested.

Anyway my "panels" consist of two frames made of 3/4 inch PVC and 90 degree elbows. Inside the frames is a soft netting i attached with zip ties. Both frames are hinged together so to speak with more soft netting between the two frames. The height of the frames is about water level and the length goes from the center point of the circular tank to the edge of the tank. There is no need to drain the tank.

One starts with them closed (next to each other) and slowly opens them to move the fish to the desired final location. This takes two people and it's imperative that you drill a few holes to make sure the PVC frames fill with water or they will want to float up.

[GaryD]

Hi Cecil,

I've seen a similar device to the one you've described used to harvest circular tanks, too. It would certainly take the pain out catching the fish......for both the fish and catcher.

I guess I like the idea of floating cages because they allow different species, different age groups and even plants to be grown in the same pool.

Gary

[Cecil]

Hi Cecil,



I guess I like the idea of floating cages because they allow different species, different age groups and even plants to be grown in the same pool.

Gary

I've used floating cages for years but have found they have some downsides. One of them is certain species of terretorial fish get very stressed in them when they reach large sizes. I've had some large bluegills (Lepomis machrochirus) beat each other up in them when they don't do it in a large tank or a pond.

[GaryD]

OK......that's important to know. Thanks Cecil.

Gary