How to Build an Undercurrent Hydroponic System

Step-by-step building instructions for how to make an Undercurrent Hydroponic System that works great for growing cannabis plants.


Getting Started

When growing cannabis utilizing the Deep Water Culture (DWC) method, one soon realizes some things will likely need to change on the next go around.

You might wish to ScrOG – or Screen of Green and do not want to move the plants to change water or check PH and PPM. Or you may have faced root rot last time, while Hydroguard and changing the water once a week will keep it in check, you do not want to have to change the water weekly either.

After investigating different Hydroponic methods, the Undercurrent method stands out above the other alternatives. Having used DWC already, this method resolves all of these issues for the most part.

The Under Current Hydroponic System utilizes a control bucket where all the water changes and adjustments take place.

Because the plants can remain stationary, the ability to ScrOG comes into focus, and by keeping the water moving, the risk of root rot is reduced and extend the time between full water changes.

How it works:

An Undercurrent hydro system consists of a bucket 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, this is for a 4-site setup. So that’s 4 plant sites and 1 control bucket.

  1. 5 buckets or totes
  2. 10 Uniseals or bulkheads (extras are good just in case)
  3. 1 10’ PVC pipe 1 ½” ( smaller PVC or tubing can be used but run the risk of the roots clogging them)
  4. Air pump and air stones. 2 per plant site are ideal, but 1 will do fine.
  5. Water pump
  6. Hoses, hose clamps, and fittings to attach to PVC.
  7. Drill bit
  8. PVC glue
  9. Net pots 
  10. Hydroton or grow stones

Step 1.

The totes used were rectangular in shape so offset the holes on the tote so it would circulate the water in each tote. Have 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.

Step 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.

Step 3.

Once you have the PVC installed it’s time to connect the pumps. Using a water pump to circulate the water, it connects to the adapter installed earlier to the pump, then from the pump into the control bucket. Also, have an air pump connected to 1 or 2 air stones per plant tote for a total of 4 to 8 air stones. The hoses for the air stones are run through holes near the top of the tote.

Step 4.

Now for the lids, using a 6” hole saw drill, run in reverse again and make the holes. They fit the net pots perfectly. Once you have those made it’s time to check for leaks.

Step 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.

Step 6.

Once the system is together and you’re satisfied there are no leaks then it’s ready for production, use Hydroton to surround the Rockwool cubes and support them in the net pots.

You will need to rinse the Hydroton thoroughly, it gets quite dusty in the bag. 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.

Let the Hydroton dry then added the seedlings to the system the next day. Soak the clean Hydroton in PH’d water first, then, if there were long roots feed them through the bottom of the net pot and add 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 use to be a couple of inches below the top of the pot so you can cover it with Hydroton as well.

Step 7.

That’s it, once you are this far it’s time to let the system do its work. 

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