Frequently Asked Questions

Background

When you refer to evidence what do you actually mean?
Is Sandponics the same as iAVs?

Yes.  Integrated aqua-vegeculture system, iAVs and Sandponics are all the same thing.   The full name is quite a mouthful, and even iAVs has no meaning for those who are unfamiliar with the method, so we decided to use Sandponics as iAVs’ street name.  Many people already know aquaponics, so we rationalised that connecting to the ‘ponics’ might be helpful while using the ‘sand‘ to describe the principal difference between iAVs and all of its descendants.

Is Sandponics the same as aquaponics?

No.  iAVs (Sandponics) pre-dates everything we know as aquaponics.  It was the first successful ‘closed loop’ integration of fish and plants.

The three principal variants on the aquaponics theme are (in chronological order)  sandponics, flood and drain and deep water culture. Sandponics utilises sand as the growing media.  Flood and drain aquaponics uses gravel, clay pebbles or other coarse media and actually resulted from a failed attempt to build an iAVs..  

Deep water culture (DWC) – also known as raft culture – has no media as such.  The plants are supported by the rafts with their roots in direct contact with the water.

Sand is not the only distinction between Sandponics.  Furrows, intermittent daytime irrigation, the detritus layer and soil microbiology are all unique features of the method.

What is the connection between iAVs and the basic flood and drain system?

Sand

How can I determine if a particular sand will drain effectively?

You build a simple sand test rig to establish its hydraulic conductivity…or the rate at which water passes through the sand.  You can learn more about the sand test rig and how it works…HERE.

Doesn't sand clog?

No.  iAVs-suitable sand…utilising furrows…and intermittent irrigation events…does not clog.

What is the correct particle size range for iAVs-suitable sand?

Sand Beds/Biofilters

Do Sand Beds Need Cleaning?
What is the working lifespan of a sand bed?

Building an iAVs

How do I size an iAVs?
How much food can I expect to grow in my proposed backyard iAVs?

iAVs has the capacity to produce fish and fresh vegetables sufficient to provide a family with 200 kg of fish and 1,400 kg of vegetables (fruit) per year in a footprint equal to an automobile parking space. *

More detail to be found in this article.

*Assumes a sub-tropical or temperate climate or controlled environment that will permit year-round plant production.

Plants

What plants can be grown in an iAVs?

The better question (and the much shorter list) is…”What plants cannot be grown in an iAVs?”

How many plants can I fit in each square metre of iAVs sand bed?

Various plant spacings are provided in Sizing an iAVS.

What bio-chemical role do the plants play in an iAVS?

As long as there are sufficient plants in an iAVs, the pH remains stable at around pH 6.0 to 6.4

When the researchers operated the systems without plants actively growing in the ‘sand-bed’ (biofilter) to act as a living (active) buffer and nutrient sink, the pH of the water rapidly dropped to levels dangerous to fish survival while ammonia and nitrite concentrations increased to toxic levels.

Fish

What fish are suited to iAVs (Sandponics)?

Any fish that can be grown in aquaponics can be grown in a Sandponics system.

What stocking density is used for Sandponics (iAVs)?

Stocking density is usually expressed in terms of so many kilograms of fish biomass per cubic metre of water….Xkg/m3. Given that stocking density is, at best, a snapshot in time (and will change on a daily basis) it is meaningless as a productivity measure.

That said, fish yields ranged from 50 to 70 kg per cubic meter of water per year (0.41 to 0.57 lb/gal/yr) dependent upon the fish tank volume to sand bio-filter volume ratio.  Each 1.0kg of fish weight gain provided sufficient quantities of all required plant nutrients to sustain 2 tomato plants yielding 5-7 kg of fruit per plant over 3 months.

What feed conversion ratio is achieved by iAVs?

 Feed conversion ratios for fish of average market size (0.25 kg) ranged from 1:1.1 to 1: 1.3…depending on the fish tank volume to sand bio-filter volume ratio.

Water

How much water does iAVs use?

Including annualized losses for evapotranspiration and incorporation into biomass (food) at 85% of total input and a seepage loss of 6%, each liter of water utilized by the IAVS technique can produce 6 g FW of fish and 17 g DW of vegetables. Collectively, tilapia and tomato yields result in 0.7 g DW of protein and 7 Cal. (or 7,000 calories) per liter of water used.

Irrigation Regime

How does the iAVs irrigation regime work?

One of the core goals of the iAVs irrigation regime is to remove not less than 25% of the fish tank volume during each 15 – 20 minute pumping cycle.  Assuming correct tank design (sloping/cone-shaped bottom) and pump capacity, all solids will be removed during each pumping cycle and the water will be crystal clear.

For example:

  • 6:00am (dawn or pre-dawn) – 1st pump cycle of the day starts)
  • 6:30am – drainage completed.  Feed fish all they’ll eat in 15 minutes
  • 8:00am – 2nd pump cycle (1/4 of tank volume, each)
  • 10:00am – 3rd pump cycle
  • 12:00pm – 4th pump cycle
  • 1:00pm – Feed fish all they’ll eat in 15 minutes
  • 2:00pm – 5th pump cycle
  • 4:00pm – 6th pump cycle
  • 6:00pm – 7th pump cycle
  • 8:00pm – 8th pump cycle (dusk or slightly after, depending on season and location).

Note: Pump remains OFF overnight.

If you provide these 8 pump cycles of 1/4 tank volume each per day, then you’ll have 2 complete tank exchanges daily and a full tank volume filtration following every feeding.  If you do this then solids will NOT accumulate nor reduce dissolved oxygen levels nor stimulate alga growth or disease organisms.  The ENTIRE point of filtration (e.g. sand) is the removal of the fish ‘waste from the water column.  The first goal is to extract the ‘wastes’, then let the sand filter out ALL of the suspended solids (including the fraction too small to see).

Why are there no irrigation events at night?

If the prescribed irrigation feeding and irrigation regimes are followed…and the system uses tilapia, carp or similarly robust fish species…overnight irrigation of the sand beds is not needed, it saves energy and provides a protracted opportunity for the sand beds to drain while still retaining sufficient moisture to sustain the plants.

It may be applicable to other fish species, too…but that has yet to be confirmed.

Research Trials

Where can I see photos of the Ratio trials?
Where can I learn more about the Ratio Trials?