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RDWC build guide

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#1 bigbadbillybob


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Posted 16 January 2018 - 04:04 PM

Hello, my fellow herb enthusiasts, I have decided to put up a short build guide for people considering RDWC.And in the vain hope that Duke will give me back my inventor medal lol. 

Now I have pictured 2 of my previous system builds, but unfortunately, the pigs stole them so I'm a bit limited in showing actual photos of various parts of the build.

I have built quite a few of these over the years, each one has been a learning process, and not without disaster along the way, as u do.

The systems shown will fit in a 2.4 by 1.2 tent (the 4 pot one) or a 1.2 tent (the 2 pot one)

These are NOT undercurrent systems, they are simple recirculating systems, utilising 22mm spray bars for the delivery and 40mm returns to the res. 


I have located the res outside of the tent in both systems, because this helps keep the temperature of the nutrients cooler, and reduces the work for the chiller (i'll come to that later)

So the system works by the process of pumping nutrient around the system, through  the spray bars. This nutrient solution is highly oxygenated, with high levels of dissolved oxygen produced by the falling water disturbing the surface tension (which creates DO(dissolved oxygen).


Now I'm not saying that this system is perfect or cant be improved upon, because nothing is perfect is it, its all a compromise in some way or other, before you all start slagging it off and telling me how I should have done this or that or whatever. I'm not really interested, ok?  good.......... then we shall proceed


Lets start with a list of stuff you will need to complete this build (2 pot system) The pictures are meant as a guide only as some of the stuff I describe is what I would do differently if I was to do it again


3No. really useful boxes (2 for the plants , one for the res) either 64 or 84 litre jobs (the more nutrient you have the more stable the EC and Ph will remain). this is why I use big boxes

A hole cutter for 22mm and 40mm pipework.

A number of 40 mm  tank connectors (6 in this case), plus 40mm pipework, bends and tees to suit. I use solvent weld fittings, which do not leak if done properly, unlike the push fit ones. The solvent weld fittings are also cheaper woop woop. the down side is that if you ever want to move the system or dismantle it, you will need a hacksaw lol.

A number of 22mm pipework fittings including bends, tees and pipework. 

I am not stating how many of each you use because it will depend on how you lay it out. I'm sure you are capable of working this part out for yourselves

A water pump _ I would recommend a 4000l/hr one for this size system, the 4 pot system I used a 6000l/hr one, but should have gone bigger.

A reducer from the water pump outlet to the 22mm spray bar. These can be bought off ebay as silicone reducers , just pump in the sizes, e.g 22mm to 26mmm or whatever it is.

Stainless hose clamps to suit this reducer, both ends.

various drill bits, a drill, 


A chiller- will depend on the total capacity of your system, for a 2 pot system I reckon you would be ok with a 150l chiller, I used a 300l one on the 4 pot system

Maxijet 1000l/hr pump and hose to suit the chiller.



Right, now to the construction part. we will start with the returns. these are 40mm, which are a decent compromise, you can go bigger (but they are expensive) or smaller (more likely to block with roots etc)

So take your really useful boxes and lay them in the tent where you want them to go, this is how I did it


As you can see the totes are side by side with the return pipes at the front and back of each box. Its always a good idea to set things out to make sure there is enough room for like lids to fit on (ahem), and all the pipework to fit  etc. Now once you know where its all going measure out your pipes, notiing where each one goes. I lay them out on the floor the way they will go in the tent, makes life a little easier.


The return pipes are attached to the box via the 40mm tank connector, which is solvent welded to the pipe When you drill the hole for the tank connector/ bulkhead, you want to try and get it very close to the bottom of the box,, BUT make sure you still have room  to screw on the nut. When you get the tank connectors you will see a rubber washer type thing - this goes to the outside of the box ok?

A word on solvent cement- you can get high as fuck off it so use in a well ventilated area (that's the health and safety pish out the way) Also, when using solvent cement, this is what I do to prevent bailing water out of the tent/ leaks  . Saw cut the end of the pipe, then sand off the rough end where all the scrappy bits are, and a small chamfer on the end of the pipe. (Use 100 grit sandpaper or above) Make sure nothing is sticking out from the pipe, like rough edges etc

Put the solvent cement on the end of the pipe, AND on the inside of the fitting it is getting connected to. Now stick em together, you don't get long.

When I join them together I kinda push the pipe in and give it a 1/4 turn at the same time. wipe off the excess glue (don't put it back in the glue pot)  Leave this for 15 minutes and it will be solid.

So glue all the returns together, putting it in the box, measuring trimming etc as you go, to be sure it will all FIT properly. No point glueing it all together then finding out your 10mm out on a measurement has fucked half of it up is there.

The returns are at opposite sides of the really useful box to equalise the return flow, so that the roots stay in the centre of the box. If both returns were at the same side of the box, the roots WILL migrate there and clog the returns. 

In the picture above you will see just below the spray bar Tee, the return pipes go to a tee fitting and then back to the res. If I was to do it again I would have 2 returns to the res, just in case the one was to block with root (unlikely tho it may be).


The picture above also shows the spray bars, the 22mm pipe inside the box which delivers the nutrients to the tote.

Drill the holes for these as high up the sides of the box as possible, you want as much fall from the water as possible. This one is drilled just below the top lip. 

These are done in a similar fashion to the returns, but it is easier to drill the holes for the nutrient to spray from before you glue the lot together. I use a small drill bit for the holes, and for this system, if I remember I had something like 4 holes on each  long side and 2 on the short sides. I had these holes drilled in such a way to spray the water around the base of the net pot, about an inch or 2 away from the actual pot itself, but its not really critical where the holes go, as long as the water can splash on the surface, creating DO.  The spray bars go to a TEE which goes to a single pipe from the water pump. A word of advice  - the pump outlet has a reducer attached, and then it goes to the 22mm pipe. You will see that this pipe goes through the side of the res. there is a reason for this, which is - if somehow the pipe detaches from the reducer, it will not go flying out of the way allowing the fountain from the res to flood the room, as the side hole will keep the pipe in place.

See pic below. Again if I was doing this again I would have the pump closer to the tent side of the box.




On the subject of dissolved oxygen, you can also add an airstone or 2 to this system. You don't really NEED to, but they help by creating yet more oxygen to the rootzone, like I did in the above system.


so that's the spray bars and returns done, you are nearly there. 

For the net pots you need to make some holes in the lids. I use 200mm net pots, and to make the hole I devised a cunning plan, baldrick would be proud of. here is how its done.

Mark the centre of the box lid, drill very small pilot hole, then get a piece of timber, and put a drywall screw through one end, so the tip of the screw ids protruding by about 3-5mm. then  measure out 95mm and put another screw through the same amount. Put one screw in the pilot hole you drilled, and then turn the wood through 360 degrees scoring a perfect circle into the plastic. Then you just keep on scoring round and round till you eventually go through the lid , or it gets so thin you can cut it with a Stanley.


Also when this is done insulate the boxes if possible, ive used Kingspan in the top pics, or even the silver reflective bubble wrap stuff for the lids is better than nothing, DO it.


chillers - you WILL need one

Chillers have a separate pump- a maxijet 1000l/hr job from the res to the chiller, and the warer will naturally return from the chiller to the res, , if you can try and get the return to make the water fall back to the res - more DO - you know it makes sense.


Pop in your net pot, fill with hydroton and grow big fuck of trees.

My first run in the 2 pot system produced 700grams from two (whisper it ) autos


Mission accomplished. If I think of anything else I will add it. 


Mon the water

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#2 Anonymiss


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Posted 16 January 2018 - 05:03 PM

I'm sure it's all very interesting but, it's pretty much invisible on the light skin...


Attached Files

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#3 bigbadbillybob


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Posted 16 January 2018 - 05:07 PM

There we go, its green now.

Another thing you might want to incorporate into the design is an ovefflow pipe (I didn't bother)

This should be located near the top of the box and should run back to the res. This will be used if , say the roots blocked the outlet pipes (not very likely to block both of them , but some people e are a bit para about stuff like floods, so if you want to, then add one.

You might sleep better


I did drill one in this system, but never used it, or fitted any pipework return.Its in the centre of the box, between the spray bars. I was gonna put a 22mm pipe from one tote to the next and so on then one from the first totoe back to the res, if that makes sense?

Don't know if you can tell from the pics, but I used rubber grommets where they spray bars go thru the box, to prevent vibration and possible leaks.
I spent ages looking for ones the right size, I remember that............


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#4 bigbadbillybob


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Posted 17 January 2018 - 01:52 PM

my latest system,, mid build, more to follow.


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#5 fairy



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Posted 18 January 2018 - 02:57 PM

nice one BBB good info that for building one ,, instead of the mark up of an Alien system lol..





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#6 bigbadbillybob


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Posted 18 January 2018 - 07:49 PM

yeah Fairy. 

The Alien system is a bit different in that its a true undercurrent system with the nutriens being pulled through the root zone by a pump, where this one is just spray bars allowing gravity to return the nutes to the res.


I used both (alien and DIY) and to be perfectly honest, there was zero difference in plant development etc.

Plain old bubblers work just as well too, but you cant regulate the res temps so easy because you cant hook em up to a chiller.


Saying that, I was offered fairly cheap, an Alien XL RDWC system , which has been modified with the big diffusers in every pot - Norres diffusers.

They create a Jacuzzi in the totes, here have a look 

Cant get link to copy and paste, but if you look up youpube Alien Xl with Norres diffuser in every pot upgrade, you will see what I'm babbling on about. I did think about it..........


but  when I did my first 2 pot system I used hose with a Y piece on the end, waterfalling into the tote, as opposed to spraying, and it too worked just as well, but its good to experiment, you know.....just iin case I'm missing a trick lol.


we never stop learning mate


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#7 fairy



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Posted 19 January 2018 - 07:28 AM

very good mate... i will look that up later...


spray bars right i get ya good idea..


never ever stop learning a constant learning hobby....

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#8 bigbadbillybob


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Posted 23 January 2018 - 11:02 AM

here is a bit more detail on certain parts of the system, which may help you decide on your shopping list.



Ah yes we all love a good old pump don't we (stop sniggering at the back) .Nothing is better than pumping 24hrs a day.

The pump is the heart of your system, and getting it right is crucial for your success with these systems.

There are various factors to consider when choosing a pump, including the total volume of water/nutrient in your system, so lets start there shall we?

If you have a 2 pot system and res as shown above (84 litre totes, but with approximately 50 litres of nutrient in them.- This depends on what size net pots you have used as they are different depths), lets say we have 150 lirtres total in the system.

For this size system I would say that you need a minimum of a 2000litre per hour pump............BUT...........more the merrier in my opinion.  Although it is possible to over oxygenate a solution, the chances of doing so without pressurised injection of O2 is minimal, so the more the merrier.

I originally used a 2800l/hr pump in this system, which was more than adequate, but if you want better penetration (of the  water you perverts), I would personally go for a 4000l/hr pump in this system.


WIth the 4 pot one, I would simply double the pump output, to 6000 litres per hour. Again I used 6000l/hr pump which was fine.

A word of warning with pumps tho- Make sure you read up the manufacturers bumph on power consumption, as these suckers run 24/7.

I was poised on the "Buy it now" for a 9000litre/hr Hailea HX8890 pump, until I spotted that this one uses 250 watts , what the fuck , that's a veg light worth of leccy, on constant every hour -no thanks.


After a bit more research I found a Hailea Eco s 10,000 litre/ hr pump which only draws 135 watts, which is still a bloody lot (but half the consumption of the 9000 litre one) 


SHOP AROUND ! And check Specs. 


You can also consider DC pumps, which are more expensive to buy, but only draw about 40-60 watts.

Also consider what type of pump you want, a submersible one or one that sits outside the res and pumps the nutrients -in  line.

I only have dealt with submersible ones when doing DIY systems, and when I had the alien system, the inline one was submersed in the header pot, so I cant comment on how pumps perform outside the res ( a lot louder I would presume).


Another factor to consider when choosing a pump is the "head" that the pump can , er pump. This will give you an idea of how powerful the pump is, which will be important for the sprayers.

typically a 3000l/hr pump has a head of 2.5 metres. this means that if the pump was submersed with the outlet above water, the water coming out of it would reach 2. metres from the floor/pump.before the flow stopped.

a 4000 litre/hr one would do 2.8 metres

a 9000 litre one would do over 5 metres, which would make a nice fountain in your room if the reducer came off, so secure all of the hoses and pipes with stainless hose clamps. 

Maximum Flow

This happens at the level of the water surface and is the flow with no pipe attached to the pump. Probably the best practical situation that closely resembles reality is when all you need the pump for is simply circulating the water. In other words there is no lift required and no significant length of pipe attached to the pump

The energy from a pump's motor is shared between flow (actually mass) of water and the height (head) to which it must be pumped. In a real pond situation it becomes a bit more complicated because when water flows through a pipe, or via a "T" piece, "Y" piece bend, fountain nozzle, or through a valve etc some energy is required to overcome friction losses in these different parts of the system.

Because the pump's motor (energy output) is fixed it means that the water flow is reduced for any specific height  (head) pumped, plus any flow restrictions (total number of bends).
Important factors for pump performance.

Use widest diameter pipe you can. Realistically 22mm is about as big as you want to go
Use shortest possible pipe length
Do not kink the pipe (a big problem with thin walledplastic pipe)
Do not use valves, T pieces, Y pieces, sharp bends etc in your pipework if you can avoid it.
Prevent build-up of algae inside the pipe by using NON-transparent piping.
When you use stepped connectors cut off the smaller diameter steps.
To totally and accurately specify a pump you need to know 3 things

(1). Volume of water flow required at the end of the line.

(2). Height to which this flow must be pumped - more for an idea of the pressure you will  get at the spray bar outlets

(3). Head (or friction loss) loss due to restrictions in pipe and fittings. Take into account any bends in your pipework. You will see that I tried to keep mine as straight as possible to ptrevent losing any pump efficiency

would be required. I would always always advise if in any doubt , then select the next size up You can always use a little extra flow, but impossible to gain flow from any given pump. 

Pump prefilters. I always use pumps which have prefilters on them, usually located under a plastic cover at the pump intake side.

​VERY IMPORTANT - Clean these out regularly, they will clog up with fine root hairs which migrate through the system.

I clean mine out with every res change. These are a sponge type construction, and would be an ideal habitat for pathogens etc, so make sure you do it.

​I just rinse mine out with chlorinated tap water, from the inside out, then just pop it back in place.


​I will do air pumps tomorrow, so stay tuned my precious water babies lol

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#9 fairy



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Posted 23 January 2018 - 02:27 PM

oi oi BBB good info there mate for the DIY RDWC


plenty of the "Carry On" jokes in there too :D

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#10 bigbadbillybob


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Posted 23 January 2018 - 07:47 PM

Cant beat a few of the old double entendres eh?

Its like being back in the 70's.

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