iAVs Frequently Asked Questions

History/Background

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

General Questions

How do I...should I...could I...? What about...what if? (and a million other variations on this theme).

We provide help wherever we can, however, we appreciate those who put in some leg work on their own behalf, too.

How long is a piece of string?

If iAVs is so good, why isn't it better known?

The precise reasons for why iAVs lapsed into obscurity around 2000 may never be known but, in the articles titled…”Aquaponics’ Biggest Mistake“…and…”If iAVs is so great, why isn’t it more widely known?”…and…”Why iAVs lapsed into Obscurity“…we attempt to provide prospective reasons.

When you refer to evidence what do you actually mean?

When we speak about ‘evidence’ we are primarly referring to The Scientific Method.

I already have a basic flood and drain system with gravel/clay pebbles. What can I do?
What sort of performance can I expect from an iAVs?

Sand

Doesn't sand clog?

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

iAVs sand has to be inert. What does that mean?

When we refer to sand being ‘inert’, we mean that there should be no chemical reaction in water that comes in contact with the sand.  We test this by taking a small sample of the sand and mixing it with plain vinegar.  If, after a few seconds, bubbles appear, then the sand contains carbonates and, because that will not allow us to operate within the require pH range, is not suitable for iAVs.  There may be other impurities in the sand that influence pH – so a simple pH test is also required.

What is the correct particle size range for iAVs-suitable 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.

Sand Beds/Biofilters

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.

Start small or just go big?

This is a common question and one that we’ve answered in Growing Your Own iAVs.

My iAVs has to be above-ground. Is this possible?

Yes.  iAVs acknowledges that, for a number of reasons, it may not be possible to put tanks below ground.

iAVs Layout Options

I have an idea that will make iAVs better.

Operating an iAVs

How important is pH?

VERY IMPORTANT – Read and understand The Effect of pH on Plant Assimilation of Elements.  If you don’t understand this, ask questions.

What sort of productivity can I expect from an iAVs?
How do I build a business based on iAVs?

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?

Here’s the list so far…

Amaranthus, Arugula, Basil, Beans (bush, heirloom, pole, wax), Beet (greens, root). Bell Peppers, Bitter Gourd, Blackberry, Bok Choy, Broccoli, Cabbage(s), Cantaloupe, Carrot, Cauliflower, Cayenne Pepper, Chinese Potato (country potato),, Chives, Coriander, Cos Lettuce (romaine), Cowpeas, Chrysanthemum, Cucumber, Dill, Eggplant (Aubergine), Groundnuts (peanut), Habanero Pepper, Honeydew, Jalapeño Pepper, Kale, Kumquat, Leaf Lettuce(s), Maize (corn), Marigold (African, French), Mustard (greens and seed), Okra, Oregano, Potato, Radish, Raspberry, Rosemary, Palak, Papaya, Snake Gourd, Snow Pea (sugar pea), Spinach, Squash (acorn, butternut, yellow, winter), Strawberry, Swiss Chard, Thyme, Tomato (all cultivars), Watermelon, Winged Bean, Zucchini

…and a host of Indian vegetables that we’ve never heard of before.

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.

How do I feed the fish in an iAVs?

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.

Is iAVs the most water-efficient food system on the planet?

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?