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Rules-of-Thumb to get started in Aquaponics.

Revised 7 May 2020.

This basic guide will help in getting started without needing to spend weeks researching.  The finer points can be studied and implemented as the project goes along.

Better still get all the in-depth knowledge by enrolling in one of my courses. 

1. My Aquaponics Master Class (face to face hands-on learning)
2. My Aquaponics Design Course (online, can be done anywhere in the world.

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 piece of advice.  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.

Rules-of Thumb…….

System type – Media bed is recommended for new, Hobby growers.

CHOP Mark2 system built from recycled IBC's

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)
3     bio-filtration (a good environment for all of those beneficial organisms that also exist in good soil)

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.
It is easier to understand and learn.

Grow Bed
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. (Complete filtration only for very small home systems).
It is best made of food-safe materials and should not alter the pH of your system (again, beware of concrete or media that has limestone content).

Fish tank
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 or media that has limestone content).

Stocking Density

20kg (22lbs) of fish per 1000 ltrs (250gal). This is a very safe stocking density for new systems.
Please do not be tempted to go beyond this stocking density. Disaster may be the outcome.

Steps for Planning your System
1. Determine the total grow bed area in square meters.
2. From grow bed area, determine the fish weight required (kg) using the ratio rule 5 kg (11 lbs) of fish for every square meter (9.5 sqft) of grow bed surface area, assuming the beds are at least 300mm (1') deep. 
3. Determine fish tank volume from the stocking density rule above.
For example, if you plan to have 2 x 1 sqm grow beds, a total of 2 sqm (19sqf)of growing area.  Plan to stock so you have a mature weight of no more than 10kg (22 lbs) of fish which will require 500-litre (125 gals) fish tank as a minimum.

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) (Expensive)
Lava Rock and Gravel are the most widely used media types. (Less expensive) 
If you choose gravel, understand it’s source and avoid media that may contain limestone that will affect your pH.

Water Flow
1. You should flood, then drain your grow beds.  The draining action pulls oxygen through the grow beds.
2. 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.
3. If you are using an Auto Syphon to flood and drain the media bed the Auto Syphon device will set the flow rate. ( this is the preferred method)
4. You want to flow the entire volume of your fish tank through your grow beds every hour if possible, but this may be difficult to achieve in small home systems under 1000 litre (250 gal) capacity.  
5. 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. Don't make the mistake of purchasing a pump that is too small in pumping capacity. As a rule of thumb for small home systems get a pump that has a pumping capacity of twice the fish tank volume,

Starting your System or “Cycling
See articles/blogs for cycling method #1. And here for fishless cycling #2

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 occurs, 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 the 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)

Feeding Rate
As much as your fish will eat in 5 minutes, 1 – 2 times per day. As soon as the fish start to lose interest in feeding.  Stop feeding.  An adult fish will eat approximately 1%  to 2% of its body weight per day.  Fish fry (babies) will eat as much as 7%.  Be careful not to overfeed 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 the most favoured.

Target a pH of neutral, or 7.0, in your Aquaponics system.  We like to keep in a range of 6.2 to 7.2 because the pH will move around and once the system is settled in it will tend to drop.
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 groundwater) or because you have a base buffer in your system such as incorrect media, media that may contain limestone).

The best method for raising (buffering) pH if it drops below 6.4
1. Calcium hydroxide – “hydrated lime” or “builder’s lime” or Calcium Carbonate
2. Potassium carbonate (or bicarbonate) or potassium hydroxide (“pearlash” or “potash”).  If possible, alternate between these two.
3. Four times using a Calcium (as above) and the fifth time a Potassium )as above) when your system needs the pH raised.  While adjusting the pH upwards, these additions also add calcium and potassium, which your plants will appreciate.  
4. While they work, be cautious about using natural Calcium Carbonate products (egg shells, snail shells, seashells). They don’t do any harm, but they take a long time to dissolve and affect the pH. 

METHOD; Mix some of the powder with water into a slurry (1 tablespoon per 1000 litres (250 gals) of fish tank volume. Add to the system as far away from the fish tank as is possible. Allow to slowly percolate through the system. Re-test pH 24 hours later and readjust if necessary.

Best methods for lowering pH, in order of preference, if it goes above 7.2
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.

It is best to be patient and wait for the system pH to drop naturally, rather adding harsh treatments like acids.

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.

I hope this proves to be helpful.  Please list any questions you may have below

This documented its original form was created by Sylvia Burnstein with input from Dr Wilson Lennard, Murray Hallam (yours truly) and TC Lynx. Unfortunately, this document has been copied by many and the credits removed.

EMAIL : [email protected]

Posted By Murray Hallam on 23rd December 2011

Updated : 8th May 2020 | Words : 1725 | Views : 8667 | Comments : 8

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Aloha Murray & thank you very much for the info you are putting out there on this fascinating topic. You are head & shoulders above the others out there. Others share the same basic info, but you present it a way that is very simple & straight forward.
I have a quick question. In a 3 bed IPC system, would it be possible to convert one of the beds to a raft system & put prawns in it, or would they eat the roots of the plants ?. I would like to dedicate 1 bed to salad greens & you say the raft system is the way to go for greens. Perhaps I could put prawns in the sump to alleviate that problem ?.
Also, why did you modify the CHOP 2 system to pump everything from the sump ?.
Thanks mate...us Kiwis love our prawns on the barby as well...lol

I live on the Big Island in Hawaii & can get prawns from OTEC

Posted By Steve McKenzie on Tuesday 25th March 2014 @ 11:19:14


Hi Steve, CHOP2 does pump everything to all points from the sump. If you want to have one bed as a raft bed that will be fine but it will cut back the filtration ability of the overall system which means you either need to add an external filter such as a simple swirl tank or similar, or cut back on number (density) of fish in the system.

Posted By Murray on Tuesday 25th March 2014 @ 11:19:14


Here's my message. Absolutely brilliant site. Can only afford Bronze as I'm out of work. But it does help me understand the processes involved, and looks like it might be a way for me to move forward. Thanks very much.

Posted By Chris Buchan on Monday 26th August 2013 @ 14:03:24


You are welcome Chris.

Posted By Murray on Monday 26th August 2013 @ 14:03:24


Can red claw be used as a fish stock or with fish

Posted By Grant Ferguson on Wednesday 21st November 2012 @ 10:50:06


Hi Grant,
Lots of people raise redclaw in their systems. Generally it is not good to mix fish species in the same tank.

Posted By Murray on Wednesday 21st November 2012 @ 10:50:06


Hello! The information is very clear, but there is something I don't get. Once I get the Fishless Cycling system started, do I have to add the fish first, or do I have to add the plants first?
Another question. If I need to raise the PH, or lower it, what percentage of calcium hydrogenated, potassium carbonate, nitric and phosphorus, or any other substance, do I need to add per cubic meter?

Posted By Noilyn Gonzalez on Friday 22nd June 2012 @ 21:22:58


Hi Noilyn,
Add the plants first, this will help take up some of the ammonium and provide a small safety net for the fish when added later. Buffering compounds such as potassium carbonate are added when and as required. It is not possible to give exact formulas as each system is different. We show how to do this in our training courses.

Posted By Murray on Friday 22nd June 2012 @ 21:22:58


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