Backyard Aquaponics
A place to discuss aquaponics

Chappo where are you?

No disputing the fact that "flow and drain in a growbed is much more efficient as it exposes huge surfaces of thin layers of water to equal surfaces of air. Growbeds are in fact huge trickling filters".

It's just that the sheer surface area required for sufficient growbeds to provide the filtration capacity to meet those sort of stocking densities will be huge...

And the capital investment required to set them up, plumb them and house them .... correspondingly large...

Then there's the labour required to plant/harvest them etc...

None of which is insurmountable.... but all factors that Jazz needs to consider... and weigh....

It may be that it is cheaper to run the facility, basically as a recirc aquaculture system...

With (dare I say it) solids removal etc... and perhaps just use the remnant water for NFT production....

On the question of flow Frank... there must surely be a point at which the energy expended by the fish stock constantly "swimming" against a flow exceeds that available to their optimum growth.....

And you can't (well I suppose you could ) cascade the volume of (Hoover dam) water into a recirc system.....

Most such systems are housed/enclosed.... to do all this you'd need acres and acres of space.... in which case you just might as well farm in ponds and be done with it...

And to compare it to schooling fish in ponds or the sea isn't comparative.... we're talking highly stocked, relatively (in comparison) small volumes water ... confined withing a small area.....

They just can't spread out if the wish too....

I hear you Frank.... but I'm just telling you that the industry has recognised that there is a finite point at which, no matter what the flow rate (with the possible exception of unlimited water supplied open ended raceways), it just isn't possible to provide sufficient oxygen beyond certain densities....

And you still haven't factored in the increased nitrogen load by continuous pumping of natural air into a limited confined, albeit recirculating body of highly stocked water...

And that holds true even for Tilapia farming... a fish that can be held at ridiculous densities....

I'm not making it up Frank.... it's what the entire industry, by consensus, experimentation over many years... and monumental failures.... have arrived at...

Go show them they're wrong.... build a better system.... you'll make a motza...

P.S. .. I didn't "omit" anything... I quoted a section from an article for the benifit of Jazz...

I have no personal investment in this... I don't farm Tilapia....

fell into my own trap here:
small sized pumps that have an efficiency of over 15 % have eluded me so far too
that is because centrifugal pumps are designed for much higher heads than what we need (3 bar = 30 m = 30 times too much)
what we need is positive displacement pumps or small propeller pumps

that it is possible to reach this kind of efficiency is shown here:
http://www.bombas-ideal.com/admincatalogos/7.pdf
but their smallest one is 7.5 kW

a typical high pressure pump will have efficiencies of over 80%

I have enhanced my excel calculation sheet (and corrected a bug) taking all this into account
also added data and comparisons on DO demands
will post V3 tonight

frank

Out by a factor of 1,000 Rupe - 15,000m3 = 15,000,000 litres! [back on the first page]

Seems to make it a fairly low stocking density [2,500kg/15,000,000l]? Something fishy with them numbers

you should probably also define efficiency

i suspect you're talking about mechanical efficiency as in X% of the rotational energy being converted into flow. you also need to compound the electrical efficiency into that.

Eg 80% (shaft power to flow) x 80% (electrical to mechanical)

there is no confusion about the word efficiency: it is the relation between energy input versus energy output
but I do agree that all stages of transformation must be taken into account as you rightly point out: the efficiency of the motor is equally important as the efficiency of the pump
I have integrated that in V3 of my spreadsheet (amongst other improvements)

With regards to that, Steve,
as we are no longer allowed to edit our posts,
could you as administrator add a line to my foremost post on
http://backyardaquaponics.com/forum/vie ... et#p149492
stating (preferably in bold red):
"WARNING ! don't download this spreadsheet unless you have checked further in this thread if there isn't a newer version
and regularly come back to look for updates."
that would be really helpful

frank

I have a CHIFT PIST system. I had ammonia issues with only 152 fish in a 300 gallon tank. Now that is with me running a pump cycle every 60 minuets; 15 min on per cycle at ~400 gallons total flow to 700 gallons of tanks. So I would say pump more often than I am.

Oh, and that problem was only recently as temps are falling. I never had a problem during the summer, but then my fish are 5 or 6 inches long now too.

a lot of confusion is caused by not only not using the same system (metric vs imperial) which is minor as it can be recalculated
but also by not using the same definitions
TMHO we should agree on standardizing:

fish well being is determined not only by the space allowed to them, but even more by the water quality supplied to them

so may I suggest (in metric):
tank space fish density to be be expressed as biomass per volume = kg/m³, (not as number and/or size of fish per volume, unless a table would allow to recalculate this to biomass in kg per volume)
more important to fish health is relative fish density, which is defined by the extra factor of recirculation: i.e. biomass per volume per hourly recirculation rate rate so that becomes kg/m³/hr

as explained there is from the fishes well being point of view a big difference between 10 kg/m³ at 1 recirculation per hour and 10 kg/m³ at 2 recirculations per hour as the amount of filtered aerated water mostly is more determining for their health than the space they live in.

biofilter capacity is to be calculated less with regards to fish density than with regards to feed rate per day (g/kg fish/day):
for the same biofilter capacity (in m³)
you may have a high density fish tank, if you don't feed them you will have little nitrification problems
if you have low density but overfeed you will have big nitrification problems

growbed volume (in m³) is determined by both biofiltration needs (for nitrification) and plant space needs for nutrients elimination
nutrients elimination is determined by nutrient needs of plants
growbed surface (in m²) is determined by plant size, planting number, planting distance and nutrient needs of plants

feed rate needs per day (g/kg fish/day) are determined by species and conversion rate (which is relative to the growth stadium of the fish)

what am I forgetting?
(I should have added "estimated" or "average" to most of these definitions as this is not exact mathematics and factors like temperature and light also come into play )

TMHO only with these data can the REAL max stocking density for Tilapia (or any other species) in AP be determined

frank