Growing with DWC requires mixing up large amounts of nutrient water. Setting up a proper DWC nutrient mixing tank makes it much easier to refill your plant reservoirs. In my old plywood grow box I only had 1x 17 gallon DWC reservoir. I used to mix nutrients and heat water in a similar-sized container and could lift the whole thing when mixing up 10 gallon batches of water. Note: If your water is above 150 – 200 ppm you may want to look into an RO system
In my current room I run 10x 17 gallon DWC reservoirs. This requires mixing up 50-100 gallons of nutrient solution at a time.
The big DWC nutrient mixing tank resembles a re-circulating DWC (rDWC) setup where you have smaller grow totes that are all connected with a large feeding or control tank. The difference with my setup is that it is just DWC not rDWC. Recirculating DWC has it’s advantages (e.g running a chiller) but for most people I recommend DWC for the following reasons:
- Run varying nutrient levels for plants that may be in different stages of flower (e.g. one tote could be in early flower while another can be flushing).
- Prevent root rot from spreading from one tank to the next
- Cater to cultivar specific nutrient requirements
- No water pumps needed
Materials Needed
- 45 Gallon (170L) tote (or size as needed)
- Ice Maker Installation Kit
- Inline 1/4″ Carbon Filter
- 1/4″ Quick Connector Ball Valve
- Bottling Spigot
- 3/8″ Tubing
- For optional Auto Fill:
- 12V Normally closed Solenoid 1/4″ Quick Connector
- 12V Power Supply (Universal ones work well)
- Float Switch
Tools Needed
For the mixing tank I use a 45 Gallon (170L) tote. It is the perfect size for a 4 tote grow. When topping off the tanks I usually add approx 10 gallons of water per 17-gallon tote.
Running Water Line
The Ice Maker Installation Kit will include a self-piercing valve for tapping into any copper or brass water pipe. It is the perfect way to bring water to your grow room. The tube will stay under pressure and prevent pathogen growth (compared to using a garden hose)
To install, clamp the valve onto the pipe with the included bolts. I had to put the bolts in backward because my pipe ran tight against the wall. Do not forget to put the rubber gasket between the pipe and valve for a proper seal. Ensure you are tapping into your cold water line and not the hot water!
Use included compression fittings to attach the 1/4″ plastic tubing to the valve. From the valve, the tubing should go to your grow room where it attaches to an inline carbon filter. A carbon filter helps remove chlorine taste from your water, which can be carried into your final product. This chlorine taste is most noticeable when making extracts such as rosin and bubble hash. For the $20-30 price tag I always recommend using an inline carbon filter.
The picture below shows the correct installation for compression fittings. Use plastic compression rings for plastic pipe and metal rings for metal pipe.
Raise up the Mixing Tank
I prefer gravity-fed systems whenever possible. Water pumps are an additional expense,point of failure and area for microbial growth. Avoid using them whenever possible. I raised my DWC nutrient mixing tank 28″ off the ground using a 2×4 frame. The dimensions of my raising table are 28″x28″x18″
Install a Spigot
Spigots are often used in homebrewing to drain 5-gallon buckets. They are readily available on amazon and hookup to 3/8″ ID tubing. Use a step drill to drill a 1″ hole in the bottom corner of your tub.
Tilt the Tank
I built up small ramp to angle the tank towards the spigot. This makes drainage easier.
Install a shelf for storing nutrients and other bulky grow items.
Solenoid and Float Switch (optional)
Filling a 40-gallon tank takes a fairly long amount of time, 30-40 minutes with my water pressure and filter. You can omit this step if you have full size plumbing running to your grow room. I caution against using garden hoses as they tend to build up more bacteria than the 1/4″ tubing that stays under pressure.
If you occasionally partake in consuming cannabis like the doc you may be liable to forget that you have the tank filling causing a slight flood in your basement. To prevent any accidents you can install a float switch to automatically shut off the water supply using a solenoid. This can be constructed for approx $30 and is good peace of mind.
The wiring diagram above shows the basic idea. The 12V power adapter causes the solenoid to open. Always use a normally closed solenoid (NC), so that if your power goes out the valve will close automatically. The float switch determines if the flow continues or not. You should also have a water valve after the solenoid so that you can manually close the water off when leaving the system unattended.
You can see my basic design above. The float switch is attached to a bigger piece of grey pipe that slides up and down the white PVC. There is a screw on the grey pipe which I hand tighten to fix the position in place. This allows me to control how many gallons I want the water supply to shut off at.
My container is 45 gallons and was 18″ tall. This made for easy math. Every 2″ I drew a 5 gallon mark
=18 inches / (45gallons/5gallons per line)
=18 inches / 9 lines
=2 inches per line
If you do not care for being able to adjust the level of water you require, this can be done cheaper using a float valve auto shut-off, similar to what is used in the DIY humidifier tek. Just mount to the top of your RO container and click the 1/4″ tubing right in.
How to use your DWC Nutrient Mixing Tank
- Spray tank down with diluted Star-San solution to sanitize.
- Fill up the required amount of water (typically 10 gallons per tote)
- If your ground water is below 60F heat it up using an immersion heater or sous vide machine.
- Add pH down to bring your pH to 5.5
- Use Nutrient Calculator and add nutrients
- Mix well
- Siphon into individual DWC Reservoirs
