First posted on November 19, 2010
It is often pointed out that it would be a good idea to have some basic rules-of-thumb for Aquaponics gardening. Why? Because they will help in getting started without needing to spend weeks researching. The finer points can be studied and implemented as the project goes along.
Sylvia Bernstein of The Aquaponic Source collaborated with Dr. Wilson Lennard from Australia to formulate the guidelines that follow below. Dr. Lennard has earned one of the few PhDs in aquaponics in the world. These guidelines have also been reviewed and endorsed by Murray Hallam of Practical Aquaponics, and the “Aquaponics Made Easy” and “Aquaponics Secrets” videos, and TCLynx and Kobus from the Aquaponic Source community site.
Nothing listed below is set in stone and there are exceptions to almost every one of the listed rules-of-thumb given certain conditions. However, they do offer a set of generally accepted principles that, if adhered to, will put you on the path towards successful aquaponic gardening.
One final caveat. These rules are intended for media-based backyard or hobby systems only. If you are intending to get into aquaponics commercially, then please seek a professional training course that will help you design an optimal system that has a chance to generate a profit.
This version of the document has been edited to metric measurements and an additional system cycling method as an alternative . An imperial version can be seen on Sylvia Bernstein’s website here.
System type – Media bed is recommended for new, Hobby growers.
Why not NFT or Deep Water Culture (AKA raft or DWC)?
A media bed performs three (3) filtering functions;
1 mechanical (solids removal)
2 mineralisation (solids breakdown and return to the water)
Because the media bed also acts as the place for plant growth, it basically does everything all in one component – making it all simple.
Media also provides better plant support and is more closely related to traditional soil gardening because there is a media to plant into.
The cost of building the system is lower because there are fewer components.
It is easier to understand and learn.
The industry standard is to be at least (300 mm) deep to allow for growing the widest variety of plants and to provide complete filtration.
Must be made of food safe materials and should not alter the pH of your system (again, beware of concrete).
If you have flexibility here, (1000 litres) or larger seems to create the most stable Aquaponics system. Larger volumes are better for beginners because they allow more room for error; things happen more slowly at larger volumes.
Must be made of food safe materials and should not alter the pH of your system (beware of concrete, for example).
20kg of fish per 1000 ltrs. This is a very safe stocking density for new systems.
(see further instructions on stocking density in our BRONZE members area)
Steps for Planning your System
Determine the total grow bed area in square meters.
From grow bed area, determine the fish weight required (kg) using the ratio rule 5 kg of fish for every square meter of grow bed surface area, assuming the beds are at least 300mm deep. Determine fish tank volume from the stocking density rule above.
For example, if you plan to have 2 x 1 sqm grow beds, total of 2 sqm of growing area. Plan to stock so you have a mature weight of no more than 10kg of fish which will require 500 litre fish tank.
Must be inert – i.e won’t decompose or alter the pH of the system.
LECA (Lightweight Expanded Clay Aggregate, AKA Hydroton or CANNA clay), Lava Rock, and Gravel are the most widely used media types. If you choose gravel, understand it’s source and avoid limestone and marble as they could affect your pH.
You should flood, then drain your grow beds. The draining action pulls oxygen through the grow beds.
If you are operating your system with a timer you should run it for 15 minutes on, and 45 minutes off. If you are running auto siphons, they will determine the time of the flood and drain cycle.
You want to flow the entire volume of your fish tank through your grow beds every hour if possible. Now consider the “head” or how far against gravity you need to move that water and use the sliding scale that is on the pump packaging to see how much more pump capacity you need.
Ammonia, Nitrites, Nitrates – after cycling,
Ammonia and Nitrite levels should be less than .75 ppm
If you see Ammonia levels rise suddenly, you may have a dead fish in your tank.
If you see Nitrite levels rise you may have damaged the bacteria environment in your system.
If either of the above circumstances occur, stop feeding your fish until the levels stabilise, and, in extreme cases, do a 1/3 water exchange to dilute the existing solution. Nitrates can rise as high as 150 ppm without causing a problem, but much above that, you should consider adding another grow bed to your system.
Be sure there is plenty of oxygen in your fish tank. You can do this through the use of a separate aeration device and by diverting part of the water from flooding and draining your grow beds directly into your fish tank. The only way you can have too much oxygen in a fish tank is if you are literally blowing your fish out of the tank. If you don’t have enough oxygen being infused into your tank your fish will be gasping for air at the water surface, but if you reach this stage you may have done permanent damage to your fish’s respiratory system.
When to add plants
As soon as you start cycling your system, but accept that they may not grow well for the few weeks required for cycling to occur.
If you add Maxicrop Liquid Seaweed to your tank when planting or Seasol at the rate of ½ litre per 1000 litres, your plants will establish themselves much more quickly. (then at the rate of one CAP full per day until system is established)
When to add fish if you are using a Fishless Cycling technique
Add fish once nitrates are present and the ammonia and nitrite levels have peaked and declined below 1.0 ppm. (see again instructions on cycling)
As much as your fish will eat in 5 minutes, 1 – 3 times per day. As soon as the fish start to loose interest in feeding. Stop feeding. An adult fish will eat approximately 1% of its bodyweight per day. Fish fry (babies) will eat as much as 7%. Be careful not to over feed your fish.
If your fish aren’t eating they are probably stressed, outside of their optimal temperature range, or they don’t have enough oxygen.
Add a handful of composting red worms to each grow bed once your system is fully cycled and fish have been added. Red wrigglers are most favoured.
Target a pH of neutral, or 7.0, in your Aquaponics system. This is a compromise between the optimal ranges of the fish, the plants, and the bacteria. For fish, this is a pH of around 6.5 to 8.0. For plants, this is a pH of around 5.0 to 7.0 and for bacteria it is a pH of 6.0 to 8.0.
Test pH at least weekly, and as frequently as 3 – 4 times per week. During cycling pH will tend to rise.
After cycling your systems, pH will probably drop below 7.0 on a regular basis and require being buffered up. If you need to lower pH it is generally because of the water source (such as hard ground water) or because you have a base buffer in your system (egg shells, oyster shell, shell grit, incorrect media).
Best method for raising (buffering) pH if it drops below 6.6
Calcium hydroxide – “hydrated lime” or “builder’s lime”.
Potassium carbonate (or bicarbonate) or potassium hydroxide (“pearlash” or “potash”). If possible, alternate between these two each time your system needs the pH raised. These also add calcium and potassium, which your plants will appreciate. While they work, be cautious about using natural Calcium Carbonate products (egg shells, snail shells, sea shells). They don’t do any harm, but they take a long time to dissolve and affect the pH. So, you add it, check pH two hours later and nothing has changed, so you add more. Then suddenly, the pH spikes because you have added so much.
Best methods for lowering pH, in order of preference, if it goes above 7.6
pH Down for Hydroponics- (be careful of using the aquarium version as this has sodium that is unhealthy for plants).
Other hydroponic acids like nitric or phosphoric as the plants can use the nitrate or phosphate produced.
Other acids, such as vinegar (weak), hydrochloric (strong), and sulphuric (strong) – last resort as directly adding these acids to your system could be stressful for your fish.
Use caution when adding anything to your system containing sodium as it could build-up over time and cause harm to your plants.
Do not use citric acid as this is anti-bacterial and will kill the bacteria in your bio-filter.