I've learned first hand and read that the most unreliable, but seemingly necessary piece of equipment in most systems is the water pump. If you want something reliable, you are going to have to spend money and be prepared to maintain the pump and nutrient delivery system. Too much work for a potentially catastrophic failure if you ask me.
I found inspiration in an instructable that I can't seem to find any more. I'm sure it was called "The World's Simplest Flood and Drain System". I would like to apologize to anyone else that I do not mention or refer to due to my incompetence, but if you see any similarities please do provide links in the comments as I do not claim to have many original thoughts.
The air pump has become a staple component in most systems for various reasons. Moving water with air makes complete sense to me while solving several issues and being cheap, reliable and easily serviceable. Pump maintenance is algae free and time will tell just how reliable.
Next, the system had to be sort of "free",so this meant parts that are common, cheap or reclaimed. Enter my friends, the pop bottle the milk bag and their goofy sidekick Aluminized Bopet (chip bag to most).
Step 1: What You'll Need
1/4 inch air tubing as required
3 ea 2L pop bottles or more as desired
1 ea pop bottle cap(reservoir cap)
2 ea Sunlight dish detergent bottle caps or pop bottle caps(planter drain)
3/8 inch inner dia. vinyl tubing as required (approx 2 ft)
1 ea 3/8 inch nylon plumbing TEE adaptor
1 x 3 length of wood or equivalent planter support
Growing medium (I use pea gravel)
Milk Bag optional
Chip bags as required
1 ea elastic (aka rubber) band
7/32, 3/8, and 1 1/4 inch drill bits (that's 1 and 1/4 inch)
Hot melt glue gun.......maybe
Step 2: Reservoir Lid
Cut ends of 1/4 inch and 3/8 inch tubing on an angle for easier feeding through the undersized holes.
Feed approx. 12 inches of the 3/8 inch tubing and a small amount of the 1/4 inch tubing through lid as shown.
Screw cap onto one of the bottles.
Step 3: Planter
Remove the "slidey valve thingy" from the detergent bottle cap, revealing the nipple over which we will slide the 3/8 inch tubing (not easy). The cap just happens to be perfect for this and fits securely over the 1 inch pop bottle threads.
Alternatively, any bottle with a nipple cap can be used as the planter itself as long as the tubing can provide a seal over the nipple or the tubing can be fed through an undersized hole in a cap w/o a nipple, also shown.
Step 4: Planter Support
I will leave the supporting structure construction up to your imagination as my skills are very limited and I do not want this to become a lesson on "How NOT to Build a Shelf". The simple structure that I built is very visible in the photo.
Step 5: Removable Planter Bag - Optional But Handy
Fill with medium and place in finished unit.
Handy for transplanting or system maintenance. It is also MUCH easier to see the water level due to the air space around the bag.
Step 6: Assembly
Connect air tube to aquarium air pump.
Fill reservoir through planters, if desired or by simply unscrewing cap and removing the reservoir bottle for maintenance. Do not overfill reservoir, it will be plenty once the plants are added.
At this point it should be fully assembled and ready to test. Test by turning on air pump and check for air or water leaks. Fill any leaks with hot melt glue.
Step 7: Operation
My timer is set to 2 minutes, but I let it run longer in the video to show what happens when the reservoir empties.
No check valve is required as it can't siphon through the air pump AS LONG AS the reservoir is not overfilled.
There is no overflow protection for the planters so a maximum level of nutrient will need to be established once filled with growing medium. This can easily be marked on the reservoir with the elastic band. Min/max levels should both be established this way. Cannot be seen well in video, but there's a max limit.
Put reservoir and planters in inverted chip bags to prevent algae growth. Double up if necessary. It works great. See DWC unit in finished system photo, but that's another story.
Due to the simple operation and modularity (if that's a word) of this system, it can easily be modified or expanded upon with ease to suit your space or container needs. PSI and volume are your main restrictions.
I apologize for the poor lighting in the video, but I have removed the bag so you can see the progress. Prepare to be bored! Especially by the last minute, forgot to edit that out, sorry.