Module 2 – Water



Water that is suitable for sandgardening is free of chemicals and pollutants.  It’s potable – which means that it’s fit for human consumption and, – by extension – fit for growing food.

Water sources include:

  • Rainwater
  • Mains – the municipal supply
  • Rivers and lakes
  • Wells and ponds

There’s everything to like about rainwater. It’s free – and it’s the water source that is least likely to contain harmful substances.

In hot arid places, it can be thought of as stored wealth. As with other agricultural harvests (grain, hay, and water) can be stored and used or sold as required.

Mains water – the stuff that is piped past your front gate – is probably the next best choice but it will usually contain chemicals – either chlorine or chloramine – neither of which is desirable for plants (or humans for that matter).

In the past, chlorine was added to the mains supply and removing the chlorine was as simple as just filling a bucket and leaving it to stand for a couple of days would ensure that the chlorine was dispersed through the gaseous exchange.

But this does not work with Chloramine – a durable compound that doesn’t dissipate in the air.

Suffice it to say at this stage, chloramine is problematic for plants, soil microbes and fish – and our only option is to remove it.

Chlorine is easy to remove by allowing the water to stand in an open container in sunlight where it will gas off over the space of a few hours.  Chloramine is the more persistent disinfectant, but the chlorine/ammonia bond is broken with the use of Vitamin C tablets – leaving them to gas off.

River water is an excellent water source for those who live at the head of the river.  For everyone who lives downstream, however, it gets progressively worse the further you go.

Contamination with human and animal waste – and the run-off from farms that use synthetic herbicides and pesticides and chemical fertilisers – often render the water unsuitable for use by those who aspire to produce clean fresh organic food.

Wells and ponds are a prospective water supply, but they can also be contaminated – sometimes by adjacent septic systems or cesspits…or high concentrations of metals.

Regardless of the source, establishing a water tank near your system will enable you to capture, store and treat useful volumes of water to be used for topping up your sandgarden as required.

How much rainwater storage?

If you’re in an arid area with periodic rains…or in a place that experiences monsoons for part of the year and parching dryness for the other part, then you need to build as much rainwater storage as your resources will allow. You have the choice of building tanks, pools or covered cisterns.

Later in the course, we’ll show you three build options…ranging from a square metre…to a 6-square-metre unit…and then an 18-square-metre unit. They will have water volumes of 200 litres, 1,000 litres and 3,000 litres respectively. We recommend that you have a top-up tank capacity of 100 litres, 200 litres and 1,000 litres respectively.

Recycled blue barrels are very useful for use as top-up water storage and dosing. They are available in 100-litre and 200-litre capacities. One or more such barrels will accommodate our three system builds.

Water Testing for Toxins

It goes without saying that this water is being used to grow food…in a recirculating system…so it’s in your interests to ensure that it’s clean. If you’re in any doubt as to whether it contains toxic contaminants, we advise that you get it analysed by a water testing laboratory.

Freshwater Tests

We need to be able to test pH…to ensure that the water in our system is – or can be adjusted to – pH 6.4 (plus or minus 0.4). The ability to measure ammonia, nitrite and nitrate levels may be useful, too.

Water tests like those in the API Freshwater Master Test Kit are used to measure these chemical levels. While these tests are not as accurate as professional-grade water titration tests, they are close enough for our purposes. Don’t bother with the ‘litmus’ paper tests – they are a general guide at best.

If you use rainwater as your water source (and we highly recommend that you do), water testing will be straightforward.

Being able to measure and adjust pH in an iAVs system is a core skill.

The Freshwater Test Kit contains pH tests (low and high-range) so it’s time to put them to use.

pH – the Critical Variable

pH is a scale of acidity from 0 to 14. It tells how acidic or alkaline a substance is. More acidic solutions have lower pH. More alkaline solutions have higher pH. Substances that aren’t acidic or alkaline (that is, neutral solutions) usually have a pH of 7. Acids have a pH that is less than 7. Alkalis have a pH that is greater than 7.

Importance of pH

For each and every organism in the ecosystem, virtually every biochemical process/transformation is influenced by the pH of its environment.  All microbial processes are influenced by pH, all plant assimilation/growth is strongly influenced by the rhizosphere pH,  and as every aquarist understands, fish health and production are also pH dependent.

pH impacts the vitality of every organism in an iAVs – each in its own unique environment – through its biochemical reactivity and stability. The pH of an environment’s water – the ecosystem – is of paramount interest in all of biology (and no less so iAVs) – at ALL trophic levels – for every organism.

The priorities when it comes to managing pH are:

  1. the soil microbiology
  2. the plants
  3. the fish

Fortunately, priorities 1 and 2 are virtually always identical – or effectively so. And just as fortunate for your purposes, many fish species suited to aquaculture will tolerate, if not also thrive, at pH levels that overlap with the range preferred by vegetable crops – and soil organisms.

So, the first imperative in a new iAVs is to establish and maintain conditions to support a robust soil microbiology.

pH 6.4 is the sweet spot for iAVs.

There are good sound scientific reasons why we manage pH at 6.4.

For the purposes of this course, pH 6.4 is the benchmark. Indeed, movement of more than 0.4 – up or down – is cause for closer investigation.

As with so many things about iAVs, we could engage in far more detailed discussions about pH but since this course is about building and operating an iAVs, all we need to know at this point is that 6.4 is the desired outcome and what we have to do to adjust it – up or down!

The best endorsement of pH 6.4 comes from a mature iAVs – where the pH will stabilise at around pH 6.4 and remain steady so long as the necessary operating conditions are met.

This is also a useful point at which to remind you that another good thing about rainwater is that it has a pH that ranges between 5.0 to 6.5 – depending on the chemicals floating around in the atmosphere. So, adjusting it for use in an iAVs is quick and easy.

pH Test Meters.

If the thought of doing lots of pH tests seems overwhelming, you should know two things. First, pH in an iAVs becomes self-managing in an iAVs within a relatively short time after startup. The next thing is that you can use a meter to measure pH.

calibrated pH meter will provide you with an accurate pH measurement in seconds. These instruments require simple but regular maintenance – and calibration – to ensure their accuracy. If they are not calibrated properly, you might as well measure pH with a stick.

Once we know how to measure pH it’s time to learn how to adjust it – up or down.

Adjusting pH

We can raise the pH of water by using calcium hydroxide – pure builder’s lime – or potassium hydroxide.

We reduce the pH of water by using sulphuric acid…or phosphoric acid.

Mix small batches of dilute solution and dose your top-up water storage – to pH 6.4. Add this water to your iAVs sandgarden whenever it needs replenishment.

CAUTION:  ALWAYS mix acids or bases into water. NEVER pour water into acids or bases…a violent reaction will ensue and serious injury is likely.

The most effective way to manage pH is to set up a top-up barrel (or barrels) and adjust the pH of the water so that is available whenever you need to top up your fish tank.

Water Hardness

If your water comes from a tap, well or pond, it may contain minerals that ‘harden’ the water – making the measurement and adjustment of pH more complicated.

The first indication of this will be when you adjust the pH of the water in your top-up barrel only to return the following day to discover that the pH has bounced back to where it was prior to your adjustment. So, you adjust it again and come back a day later and the same thing has happened. It’s right back up there again.

If your source water is ‘hard’ to the point where it resists simple adjustment, you have two choices:

  1. You commit to learning about water hardness and what you need to do to get your source water to pH 6.4.
  2. You set up a rainwater barrel or two and get started on the path to water security and quality.

Key Points – Water

  • iAVs is a ‘closed loop’ process so it is vital to ensure that the water we use is free of toxins and pollutants.
  • Rainwater is ideal for iAVs. It’s free to those who can capture and store it and it has a pH of around 5.7 (due to its exposure to carbon dioxide in the atmosphere and the acidifying effects of pollution) – so it is very easily adjusted upward to the required level.
  • A pH of 6.4 is to be maintained.

To Do:

  • Determine where you will get the water for your iAVs sandgarden.
  • Get it tested – by a water testing laboratory – if there’s any likelihood that it contains contaminants or pollutants.
  • Obtain an API freshwater test kit.
  • Familiarise yourself with its use by testing your water source.
  • Set aside a container for the storage and treatment of top-up water for the system. Recycled plastic barrels are good for this purpose.
  • Find a local source of Phosphoric or Sulphuric acid – and calcium hydroxide – for lowering or raising pH as required.
  • Investigate opportunities to capture rainwater for all iAVs purposes.