Step-by-step building instructions to make an Undercurrent hydroponic system that works great for growing cannabis plants.
Preface
When I did my first grow with DWC, I soon realized there were some things I wanted to change on the next go around. I wanted to Scrog, and I didn’t want to have to move the plants to change water or check PH and PPM. Also, they got root rot last time, Hydroguard and changing the water once a week kept it in check, but I wanted to not have to change the water weekly either.
I started investigating different methods, and the Undercurrent, or Under Current, method really caught my eye. I liked DWC already, and Undercurrent resolved my issues for the most part. By having the control bucket be where all the water changes and adjustments were done, I was able to Scrog, and by keeping the water moving constantly, I could extend the time between full water changes.
How it works:
An Undercurrent hydro system consists of buckets or totes, connected near the bottoms by PVC, and then a pump is tied into the PVC and back to a control bucket, so it constantly keeps the water flowing. The plants are in their own totes/buckets, and the control bucket is to work out of.
Materials Checklist
Here are the materials you will need for a 4-site setup. So that’s 4 plant sites and 1 control bucket.
You have two choices for seals, Uniseals or Bulkheads. Bulkheads are more expensive and more permanent. The reason I went with Uniseals is once everything is installed with Bulkheads, you have to cut the pipe and put it in a whole new pipe and bulkhead to expand. For Uniseals, you just pull the pipe out and adjust, and then you can use the same Uniseals and pipe again.
DIY How to Build
1. The totes I used were rectangular in shape, so I offset the holes on the tote so it would circulate the water in each tote. I had the hole on the right side on the front, and the left side on the back of one, and the one it connects to was the opposite formation, hole on the left in the front and right on the back (see diagram).
The holes are 2.5” wide to use for Uniseals for a 1.5” PVC. The bottom of the hole for the PVC is 1.25” off the ground. After drilling out the holes with a hole saw (run it backward and it won’t tear the plastic), then go over it with some sandpaper just to get the roughness off and make for a clean seal.
2. Time to prep the PVC. Cut the PVC to size and glue together the pieces that need to be glued together. After gluing, I had a U-shaped piece for the end, 2 L-shaped pieces for connecting to the Control Bucket, and 2 straight pieces where the totes connected in the middle. You need to drill a hole in the middle of the U-shaped piece for a plastic adapter to be epoxied in so a hose can connect this point to the pump.
After getting the PVC prepped, it’s a good idea to rinse it thoroughly to not get PVC debris in the system when you fill it with water. You will want to round off the ends of the PVC for easier insertion in the Uniseals. Spread some dish soap/liquid soap on the PVC ends and insert into Uniseal. It takes some muscle to get in, so don’t feel bad if it’s hard to do.
3. Once you have the PVC installed, it’s time to connect the pumps. I’m using a 550 GPH water pump to circulate my water—it connects to the adapter we installed earlier to the pump, then from the pump into the control bucket. I also have a 1300 GPH air pump connected to 2 air stones per plant tote for a total of 8 air stones. The hoses for the air stones are run through holes near the top of the tote.
4. Now, for the lids, I used a 6” hole saw (run in reverse again) to make the holes. They fit the net pots perfectly. Once you have those made, it’s time to check for leaks.
5. Fill the water up to an inch below the net pots and plug in the water and air pump. Let it run and watch for leaks. I let mine run for an hour but feel free to test until you feel comfortable. I saw a drop or 2 here and there during testing but just left them, and they stopped after a bit. Pretty sure some of the Uniseal just needed time to seat fully.
6. Once the system is together and you’re satisfied there are no leaks, then it’s ready for production. I used Hydroton to surround my Rockwool cubes and support them in the net pots.
You will need to rinse the Hydroton thoroughly. It gets quite dusty in the bag. I put the Hydroton in the net pots and ran water through until it ran clear, but if you’re going to use the whole bag, just open the top and poke holes in the bottom and run water through the whole thing until clear. I let the Hydroton dry and then added my seedlings to the system the next day. I soaked the clean Hydroton in PH’d water first, then if there were long roots, I fed them through the bottom of the net pot and added Hydroton, about an inch or two on the bottom of the pot, and set the Rockwool on it and gently added more Hydroton. You want the Rockwool or whatever media you’re using to be a couple of inches below the top of the pot so that you can cover it with Hydroton as well.
7. That’s it. Once you are this far, it’s time to let the system do its work. The first time I had the water all nuted and PH’d before adding plants, but after that, I just drained the water with a pump that goes on an electric drill. Then, refilled with water and nuted and PH’d with the plants in place. It doesn’t take long for the system to mix everything together.
Parts on Amazon
Air Pump
EcoPlus 1300 GPH
Water Pump
Uniclife 80-550 GPH
Uniseals
Hydro Flow Uniseal
Hydroton
Hydroton Clay Pebbles
Air Stones
VIVOSUN Air Stones
6” Net Pots
Hydro Crunch 6″ Mesh Pots
Ventilation
iPower ventilation combo
Drill Pump for water changes
Milescraft Inc. 1314 Drill Pump
Nutes, etc.
General Hydroponics Nutrient Set
General Hydroponics Liquid KoolBloom
Botanicare Hydroguard
Disclaimer: We do not promote or undertake in illegal activities.
The pump does not have to be submerged?
The water pump can either be submerged or it has the adaptor to be able to connect an intake hose and output hose instead. I have mine set up this way, I didn’t what the the submerged pump heating my reservoir at all.
It’s an inline pump
How many gallons of water did you use? Asking because amount of ph and nutes and nutes ml per gallon mix
In the beginning it was 25 gallons, now during full water changes it comes out around 20 gallons.
DUDE!!! Thank you for this very thorough writup on an RDWC.
I pretty much had an idea of how but you point right to the proper gromets and pumps and even have a nice little drawing that is pretty helpful actually.
Thanks a bunch for this and hopefully this winter we will see if I can run the DWC here.
-Pheno’s Garden Update
What did u use for a controller
Cheee! Yessah my bradah,mahaloz from nanakuli.i going give this a run come winter time
Aloha from da west side me’le farmer
I bought a water farm 8 pack and basically want to make some modifications to make it similar to your setup ..do you think it possible ? Also, do you have any issues with high water temp?
I still don’t understand the pump set up, out side the header. Also I’ve been told the uniseals leak.
Do you have any flow problems with the undercurrent as like how you offset the tubing from the outside for intrance and it’s on the inside when you exit…also having 2 exhaust for your control bucket….as companies like current culture have 1 exhaust for control with a tee fitting instead of two thankyou…
Couple questions. As your plants drink the water do you just keep topping up with just water if you feed once a week?
When you do a water change out are you draining the whole system or just the control tank?
How do you size your pump for your build
And how often do you do a water change out
i tried uniseals and bulkheads and they both leak…what am i doing wrong
Use a 2 3/8″ hole saw for 1 1/2″ uniseals the actual outside diameter if the uniseal is 2 1/2″ but that 1/8″ provides extra pressure to prevent leaks, i do something kind of like this except i just use 2 5 gal pails with pvc connecting them at the bottom with airstones in the bucket rhe plant is sitting on.
Also make sure the pipe ends are beveled and smooth and that the holes cut out of the buckets are also smooth and free of burrs and rough edges, it doesnt take much at all to cut and rip the uniseal and even a slight abrasion will produce a leak, lastly use some soap and water to lubricate the pipe and uniseal to reduce the chances if stretching the hole in the bucket when trying to put the pipe through it.
Change out neuts every 7 to 10 days if you arent able to find the sweet spot with ph and ppm balance, if you are able to find the sweet spot as your neut solution levels drop your ppm and ph numbers will remain unchanged (+ or – 0.2 on your ph reading and + or – 10 to 20 on your ppm reading isnt considered as a “fluctuation”/changed) then you can let the solution run down until droplets from the air bubbles poping on the serface no longer reach the tops of the exposed roots. This can be difficult to figure out as its different from plant to plant but it saves on nuets big time and also promotes root growth by making the roots think they need to look for more water as the solution goes down and more and more of the roots are no longer submerged
Thank you
I’m only doing 2 buckets, should I still use a 1300 GPH airpump? Each only has 1 large airstone that you recommend.
Unless there’s something I’m not seeing…. that’s not scrog… that’s just letting the stems grow straight up through a screen. If it were scrog you would have trained the stems to grow horizontally under the screen, allowing only flowers to come up above the mesh.
Would you share the parameters you are using?
How would I set up for 8 bucket system
How often do you do water changes? MY PLAN is to tether two 42 gallon cans together as reservoirs which would be 80 gallons, give or take..but if water changes are weekly or bi-weekly, should I use a smaller reservoir?
I have made a similar system but used 5 gallon circular buckets instead of the rectangular totes. Using 1.5 inch pcv with Uniseal by drilling 2.5 inch hole, I am experiencing some pretty bad leakage. Some have told me to use a 2 3/8 hole saw instead of 2.5 inch. I wanted to see if anyone else had a similar problem and what they did to stop leaking. Has anyone used silicone or something to seal between the Uniseal and bucket and the lvc and Uniseal?
Hello I’m confused by what do you mean a U shaped piece at the end where I drill a hole in.. what type of U shape piece do you mean?
It’s just a t connecting the two end buckets, the center of T goes to water pump, then back to res
if you dont understand , maybe you should not be building one…
Have you had any problems with un even water level on the buckets,
I put together a four 5 gal undercurrent rdwc when the pump is off everything is leveled once the pump is on the first bucket to receive water from the reservoir is usually higher then the next three buckets, and the fourth bucket just before the reservoir is the lowest.
Try adjusting the pressure of your pump … you might need more or less pressure to even it out
Thanks for the complete guide! I’m basing my 2 bucket + control build on this. I’ve grown before on DWC with amazing results but not full confortable with the feeding I did (got yellow leaves).
I’ve got one question; ¿How do you calculate how much to feed the plants? I’ve used AN before and it seems that full strength tends to burn out my plants.
Known this is coupe of month out, had same prod with water levels on buckets at end, slowing pump didn’t help, only way I sorted it was more connecting pipes just lower than the water level only connecting the buckets, not to the res, when then pump lowers the water level in the last bucket, extra water coming from the new top pipes equals out the water levels