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Swimming Pool to Garden Pool

When I was in Australia over a year ago, Geoff mentioned that a former student and her partner were converting their pool into a fish farm. I didn’t have a lot of time to spare, but told him I had to go. A day or so later I was poking around Vanessa and Justin’s pool, fussing about with my camera and notepad. The resulting article has since become one of the more popular ones on the site.

Perhaps there are a lot of people out there with useless, empty swimming pools? If so, here’s even more encouragement to get busy and do something with it! This family has, apparently, become self-sufficient in food production in record time – just by making clever use of their disused swimming pool.

A taste (excuse the pun) of some of the info available at their site:

The GP combines:

I totally love the idea of a closed loop food production system. Who wouldn’t? My only concern is over the hydroponic aspect – where plants are taking up nutrients too readily, as they’re in water soluble form. You could describe plants as being something of a ‘high tech’ pump. When given the opportunity, they’ll take and take until they can take no more. In the soil, this ‘taking’ is regulated by soil micro-organisms which effectively feed plant roots balanced quantities of the nutrients they require, in slow release, measured quantities. But in water, with no soil or microorganisms present, nutrient intake is not moderated. As I wrote in Soil – Our Financial Institution, excessive soluble nitrogen intake, in particular, can be hazardous to our health – even carcinogenic:

This natural process of micro-organisms feeding plants is significant, and highly complex. Through the work of these creatures a plant receives what we might call a ‘balanced diet’. To illustrate: What do you think a small boy would do if you gave him an enormous bar of chocolate to eat? Chances are good he’d keep eating it until it made him sick (even if half of it is still left on his face!). Children are unable to gauge an appropriate quantity, and will quickly scoff all they can fit in. The result? Even if he doesn’t make himself ill, your child goes on a physical and emotional roller-coaster ride until the refined sugar-induced energy dissipates. A wise parent might instead supply an appropriately sized portion of ’sugar’ in its natural state – bound up with fibrous dry matter in the form of whole fruit.

Modern agri-businesses do similar with their water-soluble fertilisers – they set a ‘meal’ before the plant that can be immediately absorbed by plant roots, essentially by-passing the balanced slow-release feeding by micro-organisms. Just like a child, this affects a plant’s health.

For example:

Pesticide residues are not the only problem arising from modern agricultural techniques. Increasingly, nitrate levels in vegetables are causing concern, although most attention so far has been focused on nitrates in water supplies…. About 70% of average daily nitrate intake comes from vegetables, compared with only 20% from drinking water. Nitrates are taken up very readily by crops, and if they are not utilised immediately in the formation of protein, they are stored in the cells in their original form. There is then the risk that when nitrates are ingested or cooked, they convert to nitrites which can potentially combine with amines to form carcinogenic nitrosamines. – Organic Farming, Nicholas Lampkin p.565.

Perhaps an even better way to describe hydroponics than the chocolate bar analogy would be to say that it’s like taking food directly into your veins, in liquefied form via hypodermic needle – bypassing the digestive processes of the stomach. The soil could be likened to the stomach in this sense – it digests and distributes food to plants.

There’s a knock-on impact, or consequence, of this form of feeding. As my Soil article continues to share, plants fed highly soluble nutrients grow fast and look great, but can be chemically imbalanced, and thus unhealthy – and unhealthy plants attract ‘pests’ and disease. Insects and fungal disease are attracted to such plants, particularly since, in addition, the environment they’re grown in tends to be excessively moist and anaerobic. Hydroponic systems often collapse because of this. Cleanliness/sanitation and isolation have been very important in keeping hydroponic systems functional, and newer hydroponic systems have begun to incorporate root sanitising systems utilising ultraviolet light or other.

Early hydroponic operations were devastated by pest problems. White flies, leaf miners, pin worms, nematodes, Cladosporium leaf mold and viruses, as well as root diseases such as Pythium root rot and bacterial wilt, were common. Today, unlike 20 years ago, the drain solution is often sterilized (Runia, 1995). The options are heat treatment, ozone and ultraviolet radiation. – University of Arizona

I’d love to hear thoughts from you guys – particularly aquaponic savvy people who understand the thoughts I’m expressing here. Ideally we’d design such a system as above, but somehow design it so soil and microrganisms can still play their role, and ensure the plants we’re getting from the system are not only inexpensive, plentiful and low-to-no input, but healthy too!




  1. Those are good questions about the hydroponic nutritions aspect. I also question the basic idea of having a greenhouse built underground. You lose a lot of light, the space is apparently hard to use efficiently (since you can see the vast majority of light falling on non-photosynthetic surfaces in the video), and I don’t see any advantage other than moderated temperatures, which might indeed be useful in Arizona.

    And his phrasing about “feeding his family of four” is misleading. MAYBE he meets his egg needs, and maybe he eats all the tilapia he wants to (if he doesn’t want to eat much), and he surely gets some veggies, but his family is not fed solely by that greenhouse, as some might interpret.

    The chicken appear to have very little vegetation to eat and whats there won’t live long. How do chicken feet react to a lifetime walking on chicken wire I wonder?

    My guess is that one could get a lot more bang for the buck by filling the whole pool with water and raising more fish. The older post about the other garden pool is much more impressive.

  2. All fish exude ammonia from their gills and waste.
    Ammonia is toxic to fish if allowed to build up in the water.

    Fortunately bacteria is not limited to just soil gardening alone and the same arrangement of bacteria convert ammonia to nitrites in water – everywhere and not exclusively to Aquaponics.

    Nitrites exist in water! Drinking water can be harmful to your health! Should we stop drinking water?! Thankfully another form of bacteria converts the nitrites to nitrates that are finally absorbed by plants in Aquaponics. Thats how the process works.

    You cannot run an anaerobic aquaponics system ever and expect to grow plants successfully – you may in fact get very sick and die. Thats why people that run real aquaponics systems pump oxygen that not only aerate fish water but through flood and drain mechanisms aerate plant roots and oxygenate the living bacteria that mineralise the plant root system.

    Its the bacteria that do the heavy work – in the soil AND in the water. Nature doesn’t discriminate between soil gardening and aquaponics.

    An interesting point people should be aware of is that Aquaponics people don’t grow food in sewers as demonstrated in that YouTube clip shown above. I would not recommend adopting that system at all. Let alone expect to feed a family of four…!

    Do not confuse hydroponics with aquaponics. Aquaponics systems mimic natural processes. Hydroponics systems requires continual purchase of expensive nutrients and sterile conditions to minimize plant disease as you have correctly pointed out in the above article.

    Where we live we have both a soil garden and an aquaponics system. Read my post on which method works best for us – given the narrow urban environment that we live in:

    Aquaponics really works! It will grow all sorts of plants easily on fish poop. Now, how nutritionally dense that food is – thats a totally different question and open to argument and worthy of further discussion.

    How do you measure nutritionally dense food anyway? Has such a gauge ever been made? (I don’t include a Brix refractometer as a suitable measurement at all) But we have eaten tasteless tomatoes grown in Aquaponics systems and Soil Garden systems and I have also eaten beautiful rich authentic flavorsome tomatoes grown in both! Without a suitable nutrition meter – I prefer to let my taste buds tell me whats good or bad…

  3. Good day
    I would like to find out if permaculture news has anything on record or archives where swimming pools have been converted to hydroponics vegetable production pools. I am requiring information on this aspect and intend to get involved in a project of this kind.


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