AutoPot® Aquaponics

by Barry (Melbourne, Australia)

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I am a fan of aquaponics. I have been for a long time. The concept of combining fish culture with plant propagation was irresistible. The concept is simple. Ammonia, the respiration product of fish, is converted by naturally occurring bacteria in grow beds to nitrites and then nitrates which are used as plant food. Cleaned water is returned to the fish tank. I have a 2250l tank supported by 11 m2 of grow beds. I use timers on large pumps to ensure that I extract solid waste from the fish tank and my grow beds are well stocked with compost worms to process that extra waste.

 

With this system I have raised Silver Perch, Rainbow Trout and currently Murray Cod. I have grown Broad Beans, Lettuce, Radish, Celery, Beetroot, Cabbage, Cauliflower, Broccoli, Garlic, Capsicum, Spinach, Leek, Coriander, Carrot, Parsnip, Rock Melon.

I have reviewed two years of operation by asking the questions: Am I a fish farmer? Am I a fruit and vegetable farmer? Or am I both? Without any hesitation, I am primarily a fish farmer. All the decisions I make regarding the system are for the benefit of the fish

Water Testing
Water quality is the number priority for fish. Closed system aquaponics requires regular testing for ammonia, PH and nitrates. The standard prescription for poor water quality is water change – dump 1/3 of the water and add new water. Then retest.

 

Fish Need Salt
Most fish need about 2 ppt of salt for ongoing health in closed water systems. Salt helps to guard fish against fungal diseases such as ‘itch’ and some bacterial problems. And of course the growbeds also share the same salt load. This salt load makes it difficult for many plants to get established, especially small seedlings.

 

Plants need more than nitrates
While nitrates are a primary plant food, most plants require additional elements for strong growth. Leafy vegetables, such as lettuce spinach and basil thrive, do well, but progress depends on grow media. Radishes and beetroot has done well, subject to restrictions of the media, but other root vegetables struggle. Fruiting plants such as tomatoes thrive, depending on the grow media, but seeding plants such as beans have struggled in my system.
One of the challenges in recirculating aquaponics systems is how to supplement plant nutrients without harming fish. The easiest solution is choice of grow bed media. I use scoria (red volcanic rock) in some grow beds, and expanded clay balls in other growbeds. As a general observation, plants grow better in the scoria than in expanded clay balls, presumably because scoria supplies essential trace elements that the inert clay balls cannot supply. At some stage in the future, I would expect the trace element supply in the scoria to become depleted, and I will have to replace it.
As observed above, I am a fish farmer. My ability to supplement plant nutrients is limited to substances that are non-toxic to the fish and do not affect the flavor of the fish. In addition recirculating systems can see the concentration of toxins in the fish, which may be undesirable to me as the ultimate consumer of the fish. Other than favourable grow media, the only supplemental feeding for plants that I have used is worm tea (from worm farm) and a tiny amount of chelated iron.

 

Media in grow beds affect plant growth
The media used in growbeds supports the colonies of bacteria required to process ammonia to plant food. It is required to be open, with many pores. Usual grow bed materials are gravel such as scoria or crushed road base, or inert media such as expanded clay balls. Materials such as coco peat have also been used, but they tend to decompose over time.
My preferred grow media is scoria. It is coarse, so provides sites for bacteria. It drains well, and provides a firm base for plant growth. However, root vegetables do very poorly in it because it is so heavy, and tends not to move to accommodate expanding roots. My beetroot and radishes that did well grew with the root portion largely above ground level. Carrots and parsnips were very short, and often had multiple sections to the root.

 

Bugs
Often I felt more like a bug farmer than a fish farmer. My most successful ‘bugs’ have been caterpillars of the cabbage moth, green and grey aphids and whitefly. Caterpillars in particular can be devastating, and can raze whole grow beds to root level overnight. Whilst I would prefer safe methods of pest control such as companion planting, traps and decoys, sometimes infestations are so bad the some extra help is required. Most insecticides have specific warnings against using around fish, and the oil or soap based foliar sprays recommended for aphids and white fly can form a film on the surface of the water in the fish tank that is detrimental to fish health.

 

Harvest Time Problems.
In equilibrium, an aquaponics system is virtually maintenance free. Fish are fed, and growbeds clean water, produce plant food and support plants. The function of the system is to produce food, so ultimately every system has to be managed through the discontinuity of harvest time. The harvest time discontinuity drastically changes either the availability of nutrient in the system, or, more critically, the system’s capacity to handle the fish load.

 

Harvesting Fish
When a significant number of fish are harvested, the amount of ammonia available for conversion to nitrates drops drastically. The bacteria colonies that convert the ammonia to plant food are not greatly affected since they are slow growing and will cope with reduced nutrient for some time. But the plants will very quickly show the effects of nutrient deficiency – plants will turn pale, growth will be spindly or dormant, and the plants become more susceptible to pest attack. Plants that are planted in ‘live’ media such as scoria do much better than those in inert media during nutrient starvation, but growth is severely constrained. As noted above, the health of the remaining fish (or new fingerlings) is paramount, so supplemental feeding of plants is difficult.

 

Harvesting Plants.
Harvesting plants is a more difficult problem. When a significant portion of plants are harvested, the nitrate requirements of the system drop. The remaining plants will only take up what they need, and the remaining nitrates will remain in solution, and reticulate back to the fish tank. High nitrate levels reduce the conversion rate of ammonia to nitrates. The levels of ammonia and nitrates rise in fish tank, threatening the health of the fish. Managing this situation requires very frequent measuring of ammonia and nitrate levels in the tank and significant water changes when the environment is becoming hazardous to the fish. In addition feed rates to the fish are generally reduced, stalling the growth rate of the fish. This situation remains until new plants are established and take up the available nutrient. Obviously careful crop rotation, continuous cropping and diverse crops can reduce the impact of plant harvesting, but ironically harvesting the fruit of the system remains one of the greatest threats to the system.

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Autopot® Aquaponics

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I want to be more than a fish farmer. I want to increase my production of fresh fruit and vegetables, both quantity and variety. I wish to achieve this in a manner that does not jeopardise my fish production – in fact I’d like to increase my fish production as well. The only way I can be both a fish farmer and a fruit and vegetable farmer is to incorporate additional systems that provide for the needs of the plants, that do not jeopardise the health of the fish, or lose the symbiotic relationship that is core to aquaponics.

My solution is a hybrid of classic recirculating aquaponics and plant driven Autopot® hydroponics. I have retained my existing aquaponic and will use that for growing leafy plants that love the high nitrate food environment. Then I will use an AutoPot™ Smartpump set to deliver balanced nutrient to a variety of plants as their need dictates. I will draw nitrate rich water from
the fish tank, ensuring a continual stream of fresh water to replenish the fish tank.

 

My Autopot® system currently has 60 endpoints that serve fruit trees, orchids, bulbs, flowers and a wide range of vegetables. These endpoints consist of:-
1 x CapPlus Table.
9 x Hydrotray Single 12" modules.
22 x Hydrotray Double 10" modules.
12 x Window boxes.
7 x Smart-drippers.
8 x Hanging Baskets.
1 x Experimental Potato tub

 

Although it appears that I have a large number of endpoint on my Autopot® system, it does not use enough water in winter to replace the need for grow beds. Remembering that Autopot® is plant driven and nutrient/water usage determined by each plant, my winter water consumption is less than 50 litres per day. The hybrid system is expected to address many of the issues identified above.

 

Water Testing
The hybrid system will ensure a 2% per day water exchange in the fish tank in winter and an estimated 10% daily water exchange in summer. With this amount of exchange, I would expect almost no reason to have to dump water, and water testing to drop to a very low level.

 

Fish Need Salt
With continual planned water exchange, it is expected that the system will not accumulate pathogens harmful to the fish, so no salt will be needed. This is essential since Autopot® plants would eventually accumulate salt to toxic levels if the fish require continuous salt.

 

Plants need more than nitrates
The Autopot® system delivers nutrients directly to the plant, which takes up nutrient at the rate each plant requires. The A/B Autopot® nutrients provide the full range of trace elements essential for vigorous plant. These are delivered to Autopot® plants without jeopardising fish livelihood. Plants retained in the grow beds will be nitrate loving plants that can thrive without extensive extra nutrients. At some stage I may investigate lowering the nitrogen content of the A/B nutrients, but this is certainly not required in the early stages.

 

Media in grow beds affect plant growth
Plants in the Autopot® system can use a wide variety of growing media, since the media is not required to provide anything more than mechanical support for the plants. In fact there is some demonstrations of plants in an Autopot® system with no media at all. In my system I variously use potting mix, coarse orchid mix, sand, scoria, Perlite, Vermiculite and expanded clay balls depending on the needs of each particular plant.

 

Bugs
Autopot® plantings help me to address the bug problem on several fronts. Firstly strong healthy plants are naturally more bug resistant. Secondly, the Smart-Pump allows me to distribute plants quite broadly, so migration of pests is reduced. Finally if severe circumstances force me to take active measures to eliminate pests (soapy or oil foliar sprays, dipel {for caterpillars} or stronger insecticides) then the Autopot® plants are both further away from the fish tank, and do not reticulate to the fish tank, so fish health is maintained.

 

Harvest Time Problems.
Autopot® resolves most of the harvest time discontinuity problems.

 

Harvesting Fish
Plants on the Autopot® system are supplied with A/B nutrients, so a drop in nitrates has little effect on their growth rate. Obviously plants in the grow beds will experience nutrient starvation after fish harvesting, but this is only a portion of the systems fruit and vegetable production.

 

Harvesting Plants.
The hybrid Autopot® system ensures a continuous water exchange, so nutrient surges with harvesting plants from the grow beds will be moderated by this. The system may need closer monitoring if significant harvests are made from the growbeds. Harvesting from the Autopot® points will not affect the nutrient load in the fish tank, other than to temporarily lower the degree of water exchange in the fish tank.