Aquaponics "Mythconceptions"

[Dufflight]

2x JVP-102B 5000lph For the inside tank, but will put them in the swirl filter first to see what happens with 10000lph water pump and 2x 5000lph jets do.

[GaryD]

Hi,

As Castaway evidenced in his (faintly hysterical) comment on my blog post Mythconception #6 – Aquaponics is Easy, not everyone is comfortable with my suggestion that it might not be as easy as some people have been told……or have been telling other people.

BYAP contributor TCLynx has gathered several of the more commonly held notions about aquaponics together in (what I suspect is) an attempt to make sense of the “guidelines” (read Mythconceptions).

While I commend her for her efforts to make aquaponics more understandable, her post illustrates the difficulty in attempting to formularise aquaponics.

MAX fish stocking per minimum grow bed/fish tank volumes
3 kg of fish per 100 liters of flood and drain media filled grow beds with 50-100 liters of fish tank
(1 lb of fish per 5 gallons of flood and drain media filled grow beds with 2.5-5 gallons of fish tank)

My experience suggests that the stocking rate is dependent upon water quality, and that is influenced by many things. It is simply not correct to say that you can load 3kg of any fish species into 50 - 100 litres of water serviced by grow beds with a capacity of 100 litres.

At the low end, that may mean that you have a stocking rate of 6kg per 100 litres (based on the 3kg at 50 litres). While you might be able to keep certain species at that level, you certainly couldn’t keep others at that rate for very long.

Ratios
When we talk about ratios it is grow bed to fish tank. A 2:1 ratio means there is twice as much grow bed volume as fish tank. Yes, if you have twice as much grow bed as you have fish tank, you then need a sump tank or some other means to keep from running the fish tank dry.

While this is a common generalization, it may not be sustainable in certain situations….particularly at a stocking rate of up to 6kg per 100 litres.

Pumping
Pump the volume of your fish tank each hour (if pump is running on a timer, pump should move the volume of the fish tank in whatever fraction of an hour it is turned on.)

Once again, the required turnover rate for the water in the fish tank is driven by the particular circumstances of a given system……and that may mean that the water might need to be turned over more (or less) frequently.

Aeration
Though flood and drain grow beds provide all the aeration that the plants and bacteria needs, it is good to have supplemental aeration for the fish tanks even if it is not strictly needed to keep the dissolved oxygen up for the fish, the extra circulation provided by the aeration can help keep fish tanks cleaner. Also having a supplemental air pump can make it easy to hook it up for battery backup in case of power failure.
-1 cfm (cubic foot per minute) at 2 psi (pounds per square inch) for 400 gallons of fish tank.-
?aprox 18 liters per minute at 13 kPa for 1000 liters of fish tank

I agree with TCLynx’ general proposition of having plenty of air in the system.

Grow bed Depth

A relatively standard depth for grow beds is 30 cm or 12 inches. This seems to be a good minimum depth that provides plenty of dark space for bacteria, solids filtration, and root depth while still allowing for dry media on top and when using siphons, constantly flooded media at the bottom. It is possible to use shallower beds but they have greater challenges. Deeper beds are definitely functional though they provide less planting surface for the same amount of gravel. Deep beds are a good choice for those wishing to place DWC or NFT growing space after the deep grow beds.

All of the attributes TCLynx states for 300mm grow beds hold true for shallower ones, too. The challenges to which she refers are minimal and the benefits of using shallower beds (depending on the circumstances) may be significant.

Solids removal
Highly debated topic
If plenty of flood and drain media beds are used, solids removal is not needed.
However, if trying to grow lots of fish with minimal filtration, then the added complexity and labor of solids removal becomes necessary.

What does plenty of flood and drain grow beds mean? What does lots of fish mean? As I’ve already demonstrated, taking TCLynx' assertion that you can keep 3kg of fish in 50 litres of water (equal to 6kg in 100 litres) could be a potentially catastrophic prescription in itself.

As I’ve already pointed out many times, grow beds are bio-filters and heavy solids loadings will impair the performance of bio-filters.

So, we come back to the point that it is simply not possible to generalise around aquaponics.

The problem, as I see it, is that some people are unable to grasp the simple fact that aquaponics is not as simple as they would like it to be. Others understand this, but obviously feel that it is not in their interests to have people believe that aquaponics may have its own (sometimes protracted) learning path.

As someone with a broad interest in backyard food production that spans 30+ years, that realisation neither surprises nor dismays me.

I’m used to the fact that each food production discipline…..be it chickens, quail, vegetables, snails, cattle, fruit trees, sheep, goats, grains, aquaculture, rabbits, herbs, fungi, hydroponics……has its own body of associated knowledge and skills that have to be learned and mastered for successful consistent production to occur.

Let’s take poultry production as an example. If we were to take an aquaponics is easy approach to poultry production, we might say that poultry:

• produce 200 eggs per year
• take 19 days to hatch
• need to be kept at a temperature of 28 degrees C
• feed should be about 19% protein
• grow to 1.5kg in 60 days.

When we get into the detail of poultry production, we discover that:

• some species of poultry produce up to 300 eggs per year while some obscure species of geese struggle to produce 20 eggs per year.
• Chicken eggs take 21 days to hatch while those of Muscovies take 35 days.
• Day old chicks/ducklings/poults need to be kept at around 35 degrees C while adults can (depending on the circumstances) sustain anything from below freezing to 40+ degrees.
• Broiler chicks will require feed with a protein level of 22+% while laying pullets will require something like 17%.
• Broiler chickens will grow to processing age in 35 days while a goose may take six months.

If you were to apply the simplistic formula that I described earlier, you would have dead birds everywhere…..and a stinking mess to boot.

So why would we expect aquaponics to be any different?

-o0o-

[GaryD]

Hi,

For those who may be interested......you can see my latest blog post "Mythconception #7 - Grow Tank Depth".....here.

Gary

[Dufflight]

Only thing I see is one is talking Hydro and the other side is AP. Shallow may work well with both but I would think the temp would be more stable with a greater depth. Fish wise I like the more stable enviroment. There are also a lot of mtr + ones with the fish under the rafts. This way the fish keep a lot of solids from settling on the bottom. The roots I expect must be protected.

[damien little]

I can understand the reasons for growbed depth of 300mm, but I see no reason why 300mm floating raft troughs would be any better than 200mm. If the parameters are the same in each trough, ie flow rate, airation, nutriet levels etc, I would strongly doubt any difference could be seen between 2 troughs of different depths. As for temp stability etc, most rafts are polystyrene, and with the flowing water etc, I doubt the shallower ones would get any more or less temp fluctuations. I haven't seen anyopne actually claim 300mm troughs are neccessary, but I assume they have somewhere (links please)

Damo

[GaryD]

Hi,

For those who are interested.......my latest blog post....Mythconception #8 - Water Turnover......here.

Gary

[GaryD]

Hi Damien,

Here's one place it cropped up......here. It's not so much a suggestion that they must (or even should) be 300mm but rather the lack of logic that attended the reasons offered. The depth of grow tanks (like any other aspect of aquaponics is driven by the circumstances that apply rather than any formula or 'guideline.'

Incidentally, for all of the suggestions that grow beds should be 300mm deep, it's worth noting that, as far back as the 1950's, flood and drain gravel grow beds were used in hydroponics.....and, according J. Sholto Douglas (in his book Hydroponics - the Bengal System) they were 200mm to 225mm deep

Gary

[Dufflight]

But hydroponic GB's don't need to work as filters and house bacteria and a lot of them are in glass houses so don't have to deal with a lot of wind. 100mm more sounds okay to cover the difference.

The water turnover of once per hr is something I had a problem with. 55000ltr pumped every hr is a lot of water. I incorporated airlift bio filters to help with this and run a ratio of 9:1 for water to media. But on a standard system it helps cover the basic rule of keeping the beginners system running well. My system cycling took months to get to a safe area. One of the reason I left adjusting the PH down till now was the bacteria worked better and keeping the fish happy was my main goal.

[GaryD]

Hi,

Castaway fired off a somewhat shrill response to my blog post Mythconception #6 - Aquaponics is Easy when I posted it some weeks back. He seemed genuinely offended that I should utter such heresy.

I see that Murray has conceded that "It is not always easy"......so I guess Castaway can relax now that he's heard it from someone whose experience confirms that it really is not alway easy.....despite what the brochures might tell you.

Gary

[Dufflight]

Self sufficiency is not easy. I do find AP to be easy when we take the time to learn the basics. But we all tend to get caught up in the excitement. And that is where most of the problems lay. I do think AP is a key in self sufficiency, with more control over growing plants and fish. And its ability to enhance other forms of growing. Some people will always be happy with just doing AP. Others still like dirt, I'm more for both and anything in between.