Backyard Aquaponics
A place to discuss aquaponics

Yes they are in Victoria.

But you get a "Aquaponics university course" and you "only" need the skill of a carpenter/cabinet maker.

Seriously what is the "CAD pump" Colle Davis invented?

"CAD" pump?

Googling on "CAD pump" comes up with just different types of "positive air displacement" type pumps.

Seems like just a custom type of geyser pump? or a combo of air lift and geyser? that just sucks out the fish poo for a limited amount of time (30 minutes)? Their "settling tank" is like Travis's barrel ponics flushing tank? but using a siphon to drain out in 30minutes?

I'm thinking some kind of pump working 24/7 is more watts/gallon efficient (?), instead of periodic pumping(?) due to the required start up energy needed for a periodic pump.

But I'm wondering which of the many types of continuos pumps are the most efficient in terms of electrical use (watts per gallon)? Just in general as a category, impeller vs airlift vs geyser? I think there was some discussion in the past?

Any thoughts?

Have any design principles emerged for DIY airlifts and DIY geysers? In terms of gallons per 12 hours?

About "their grow beds", seems like a flood in 30 minutes and drain for 11.5 hours? A syphon? Stand pipe with a hole at the bottom?

Any other interpretations of their system description?

thanks BH, pumping water takes power, solids pumps are less efficient, so an air lift will have advantages.

I would be interested to see the cycle flow rate.

It looks like they have put a lot of work into optimising there system.

1 fish per gallon and 5" deep grow beds, very lean IMO.

Lean in deed! One gallon of water per mature fish? A gut feeling says there is no room if things go wrong.

Still trying to figure out their "device" in the growled. They say the water level "triggers" to empty the bed.

Just a stand pipe with a hole at the base? A bell siphon ?Drains out in 11.5 hours?

If the bed is 200 sq feet by 5 inches that works out about 83.3 cubic feet of media.

How much water in a cubic measure of 3/4 inch gravel? 40-50-60% ?

That would be the size of their "settling tank". The amount of water their "pump" puts out in 12 hours

40%-34 gal over 12 hours, 2.0 gal per hour?
50%-41 gal , 3.4 gal per hour
60%-50 gal, 4.17 gal per hour

Can an airlift do those rates?

Can a Geyser pump do it?

If yes how much air has to be moved? At how many watts continuous?

Then there's the amount of head to deal with.

Bob H, I think you will find that volume of water in a given volume of media, such as 15-20mm gravel, works out to around 30-35% of total volume.

Thanks PLJ!

I'll have to rework my numbers. I'm thinking I'm off by more than just the proper % to use. I think I calculated cu ft to gal incorrectly.

Still looks like a very lean system and no room for problems.

Gave some thought and watched some videos about their system and other DIYers.

If I understand RupertOz statement correctly that settling tanks/clarifiers are normally used just before a DWC and NFT. That seems to make more sense. One would think the solids should go into the grow bed and let worms do what they do and solve the "solids problem".

So the clarifier/settling tank size is dependent on retention times and not the "charging volume" going into the grow bed? One thing I don't understand is if all the junk is sitting in a clarifier, wouldn't anaerobic digestion be going on, polluting the liquid going into the grow bed? Reducing dissolved O2? How much conversion of solids to liquids would actually take place?

In another video PF said the plants in their beds can survive a 24 hour failure to flood. So some water is left in the bed? How much? That would reduce the amount of water needed to be pumped in 30 minutes.

Back to the flow thru rate...

200 sq ft * 5 inches (0.4166) = 83.32 cubic feet of media

83.32 * 30% = 24.996 – 25 cubic feet of water in grow bed

25 ft3 * 7.48 = 187 gal water in grow bed

83.32 ft3 * 35 % = 29.162 - 30 cubic feet of water in grow bed

30 ft3 * 7.48 = 224.4 gal water in grow bed

(Not allowing for the usual 1 or 2 inches below the gravel to control algae)

So they are pumping somewhere around 187 to 225 gallons (worse case) in 30 minutes out of the fish tank 2 times a day? That doesn't sound right.

That doesn't allow for standing water in the bed, so the actual rate would be less? So how much water can plants sit in and therefore reduce the amount of "Charging water volume"? So one can't be really sure of their flow thru rates for that system?

That 2 times a day surge doesn't seem very energy efficient?

Can fish really do well in fluctuating levels in small tanks? Seems like the tank would need more capacity and therefore more water per fish than a constant height fish tank. Therefore the fish would be less stressed in a constant height?

Their "flow thru rate" must really be small. What is a typical flow thru rate for an NFT channel "x" inches/mm wide? Typical flow thru rate for DWC? Is their system closer to or lower than rates for NFT? Closer or lower than DWC? TCLynx had some success with just a batch of uncirculated water without supplemental air. So if DO is not a problem ( because they empty the bed and put additional air into the fish tank) then it's just a matter of how fast the plants take up the nutrients?

So like slowboat said what is their flow thru rate?

I must be missing something AGAIN. What am I missing?

Any thoughts?

Absolutely... unless the "junk" is bled off... the filter cleaned...

This is the case with all solids trapping filters.... radial flow, box/brush filters... even aquaculture filters... or the "bird netting" settling tanks utilised in most raft systems...

They all must be "cleaned" at regular intervals...


The typical recommended flow rate for NFT is 1-2L/minute.... per channel...

Thanks for the info RupertOz,

How wide is a channel? How long a channel? How many "holes"? Does the number and frequency of holes then depend upon the crop? i.e. leaf lettuce, head lettuce, other leafy "short" plants?

In your opinion are the rates 1-2 l/min, per width, per length, solely dependent upon O2 being depleted?

And/or are the nutrients in the water barely if at all depleted by the time it gets to the end? I imagine you don't want to run out of nutrients at the end of the channel?

Sorry for all the questions, just don't know the realities.

Commercial NFT channel width varies from manufacturer to manufacturer Bob....

Typically.... 100x70... 150x70... jumbo channel (tomatoes/bell peppers/brassicas)... 225x75...

Usually supplied in 6 metre lengths.... typically with 200mm spacings for leafy green crops... 20 holes/6mtr channel...

Typically 2 lengths may be "butterflied" into a 12 mtr length which is pretty standard... (sometimes longer)

For reasons of O2 depletion, nutrient depletion... and ambient heat gain... (which affects DO solubility.. and nutrient)

A lot depends on climate/heat gain.... and transpiration losses.... the flow rate of 2l/m would usually be used in high heat/transpiration situations...

The 1l/m rate is more typical for most applications/crops...

Thanks for the numbers RupertofOZ,

I'll have to make revisions in the theoretical "PF's charge volume" for algae control and some low level of standing water.

I want to spend some more time using your numbers and crunching some possibilities.

Theoretically, what if we replace PF grow bed dimensions with NFT "nutrient widths and lengths", (not the overall width of the NFT channel itself). In other words one large "NFT channel" equals the width and length of their grow bed. Then we calculate the total volume of water pumped over 11.5 hours using ideally, one liter per minute/normal NFT channel.

Another option would be to compare flow thru in a DWC.

What are reasonable flow rates and dimensions of a DWC? Is that pumping more or less than NFT pumping rates? I have no idea.

Just for arguments sake, make an assumption that the supplemental O2 that's pumped into a normal DWC is in fact satisfied by lowering the grow bed water level periodically.

I'll have to crunch the numbers later tonight. If nothing else comes out of this I'll have a better handle if I want to do NFT and or DWC in my greenhouse later.

Eventually can we ask if PF developed a true paradigm shift in media based grow bed design? They are growing stuff but how?

1.5 inches for algae control – no water

0.5 inch residual water/ static layer

so 3 inches of charge space 3/12 = .25 feet

so 200ft3 * .25 feet = 50 cubic feet


……so 50 ft3 * 30% = 15 cubic feet of “charge” water

…..5 ft3* 7.48 = 112 gal of “charge” water

112.2 gal per 30 min = 3.74 gal per minute to “charge”


50 ft3 * 35% = 17.5 ft3 of “charge” space

17.5 * 7.48 = 130.9 gallons of “charge “water

130.9 gal per 30 min = 4.363 gal per minute to “charge”



I gallon = 3.785 liters

112.2 gal= 424.677 liters of charge

130.9 gal = 495.4565 liters of charge

1 liter per minute * 60 * 11.5 = 690 liters per channel

so their flow rate is way under NFT rates?

so where are the O2 and nutrients coming from and how are they getting into the plant (assuming we are not going to worry about nutrient levels)

so I started reading up about what Rup said about temperatures etc. One thing led to another starting with;

http://www.quickgrow.com/gardening_arti ... evels.html

then

http://www.just4growers.com/stream/hydr ... onics.aspx

which led to;

http://www.ctahr.hawaii.edu/hawaii/down ... ettuce.pdf

and

http://www.instructables.com/files/orig ... 2VW4QQ.pdf

Then some how I stumbled across an article from Egypt combining DWC and NFT with interrupted flows;

http://www.acss.ws/Upload/XML/Research/485.pdf

PF doesn’t use cavities but what if they leave enough water at the bottom and the rock acts like the researchers built-in dams? The next wave of nutrients would flush out the cavities. So a new flush in a flat bed of rock would flush out the spent nutrients and O2 levels in the static layer? Sherif was able to get several hours of stopped time depending on the type of plant. So how does PF manage to stretch it out to 12 hours?

I am disappointed that the author didn’t talk about how many liters per minute was used for the continuous flow NFT. Was the NFST flow rate for 30 minutes the same as the NFT flow rate? Yes?

What do you think?

Anyone ever experiment with "ebb and flow" with a bell syphon or stand pipe?

a bit reluctant to give these guys more oxygen but I see they now promote their system as commercial, using GB's?

note they don't include the cost of the AP university course.

Crap like this makes me want to shoot myself in the face....