Backyard Aquaponics
A place to discuss aquaponics

Deep Water Culture (hereafter referred to as DWC) is pretty much Floating Raft Culture. But with larger plants, and more rootspace to grow.

As with any hydro type system, there are many variants...

My interest in DWC sprung up when I realised the additional buffer it could provide an Aquaponic system by having large volumes of water in with the plants side. And this being exchanged with the fish water. This would effectively make a highly stocked tank safer as the actual water volume was more than that of the tank.

ie: 200 litres tank stocked at 4 kg per 100 litres = 8 kg fish. This should support 10 buckets nicely. Maybe even more

10 x 5 gallon bucket planters will hold a further 17 litres of water each. Total system volume of water is 370 litres.

As you see, this has got to be good for your fish.

But what about the bio-filter?

Most of the bio filtration is attached to the plants root systems. These get huge. A net pot (larger the better within reason) holds some medium to assist in 'anchoring' the plants.

Bear in mind the above figure of fish is to support 10 fully developed fruiting plants. Due to the nature of DWC bio-filtration being mainly located in root systems it is better to add two more planters. Rotate the crop keeping 10 of the planters full at all times and eat your fish as they outgrow your planting space.

Harvesting constantly produces more fruit but also benefits the filtration as the plants will feed more to produce more.

OK, I have things to do for a wee while.

Will be back soon with system parts, parameters, problems, and quirks we can look at.

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The bigger boys made me do it.

This will be a very valuable discussion.

DWC water level in the planters does not change.

Here is the singlemost cause of root rot and crop failure in DWC I have seen. Why? - Water roots can turn into air roots - but air roots cannot turn into water roots.

What this means is that if your water level dropped in your planters, water roots would begin transforming to air roots within minutes. When the water gets 'topped up' again - the air roots drown.

Another note on this point.

Your plant will want room for a layer of air roots as well.

Planters need to be designed keeping both of these points firmly in mind.

The exit point of the water is level with the line between air and water roots. Air root zone should be 65-70mm deep. This means your exit point should be centred at 65-70mm below the top of your planter.

Here is one way to do this.

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The bigger boys made me do it.

Alternately you can exit water from other points on the planter provided the plumbing is completely sealed and comes back up to the correct level before returning to your fish.

The above picture also allows for good water flow with water circulating down and around the planter before exiting.

Waterflow is crucial for DWC

Water brings air and without it your plants would soon drown. A typical changeover for 10-12 planters is 10 - 12 times per hour.

It is the volume in your buckets, not your fish tank, that calculates the recirculation rate.

So to get a pump for 10-12 DWC Aqua tomatoes.

Approx 200 litres times 12 times per hour.

note: A bit too much flow is better than not enough.

A 2400 litre per hour pump. But Wait!

Always remember your pump loses capacity when it must perform at height AND you want a Venturi Nozzle for aeration taking further power away from your flow.

Add 20% for your aeration. - 2400 lph plus 20% = 2880 lph pump.

In this instance I would be looking for a pump that performed at 3000 lph at the head required.

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The bigger boys made me do it.

Can you post a picture of a venturi nozzle AA. I have seen diagrams, but would like to see what materials are used.

Thanks.

AA - after much searching I found where u posted the diagram of the funnel sort of return with venturi to be used with waterfall into fish tank. This won't really be suitable for the DWC buckets will it. To create the venturi do I just need to reduce the width of the water pipe a bit at the point of entry into the bucket and then provide a vertical pipe off that for the air to come in. How do I make sure that water does not spirt out that pipe due to pressure build up?

I don't have a camera I borrow one sometimes.

It is extremely simple but one of those things, once you get it - TWIG!

A small hose is fitted to the side of a larger hose. The larger hose is your pumps inlet is the easiest way to ensure it wont spurt. The pressure of the water being pumped pulls air in through the small hose.

You could make one using

a T join of the large hose size (size of pump outlet)
a reducer from the T join size to your air hose size.

ie

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The bigger boys made me do it.

Thanks AA - what stops the water from wanting to go up the small pipe as weel - particularly if you have decent pressure (or god borbid, you get some sort of obstruction. Do people use 1 way valves to stop this?

You could I guess. Water will follow the path of least resistance. If the main flow has an exit, and the air intake is higher than the exit of the flow, there should be no spurt. Test it.

A venturi plumbed between your pumps intake hole and pump is dynamite in filling your water with air. Take the outlet hose off once you get one sorted and see, massive aeration.

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The bigger boys made me do it.

Okay AA - so you would probably only have 1 venturi to service the whole lot, not 1 on each offshoot pipe going to each bucket.

AA, having it on the inlet side soundls like an easy way to guard against water sputing out, but might play havoc with the impeller, sore of like cavitation...........

trick is to have very fast flow down the large pipe and very small hose (pipe) as the venturi, sometimes the tip is also cut at a 45 degree facing opposite to the water flow. many venturi have a venturi "throat" AA you would be better than me explaining this, maybe a pic, but i think it would be impractcal to go that far with pvc, and its probably not needed.

AA sounds like he has the hands on experience, i'm just regurgitaiong theory.

The theory goes that a faster flow has less pressure and vice versa, picture a 20mm pipe joined to a 10mm pipe joined to another 20mm pipe.

if you could T into each pipe and measure the pressure you would see that at the 10mm pipe the pressure would drop (because the velocity increases) and then go back to (almost) the original pressure at the next 20mm pipe.

trick is to have the flow velocity fast enough to actually suck in air from the atomsphere. its the system that spa baths use to create the bubbles.
And the system that the oldend days fly spray pump thingy used, incredibly fast air velocity over 1/16 inch tube sitting in the flyspray liquid, pressure drop was sufficient to actually suck the liquid up.

ratio of air inlet hose to water flow hose to water velocity is the key, but i have no actual data.

Oh, and technically the flow velocity is greatest right at the centre of a pipe, so if you can insert the small tube to that point is should give you the best effect. (going back to first year instumentation here, flow module........stretching my memory )

(just posted this incase anyone was as much of a freak as me for NEEDING to know how things work )

Steve

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The only tool you need is a paperclip

Plumbing between intake hole and pump is not really practical for me as I have a submersible pump which has the intake in the pump. Could plumb it soon after the pump though and therefor have the air intake pipe over the tank, just in case the water decided to go out that pipe.

Will rig one up sometime soon. To see it is working, will I expect bbubles coming in the water coming out the end?

Yep, just like a spa jet with bubbles

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The bigger boys made me do it.

Re Venturi,

BERNOULLI'S PRINCIPLE

See Venturi explained

Maybe this link will help understand a venturi

Mojo

venturies are helpfull, but in no way manditory.

if anyone wants to experiment with dwc, besides using the raft mathod, ya could take a 5 gal bucket, drill a hoot load of small (3-4mm) holes in the bottom, put an airstone in the bottom, net pot in the lid, and submerge the bucket in a fish tank.

the roots will grow out of the net pot into the bucket, and the bucket will protect the roots from hungry fishes.

water lavel is set at 1" (26mm) above the net pot until the roots grow out, then the bucket is raised (dropping the water level in the bucket) to 1" (26mm) below the net pot.