How To Build A Floating Raft Deep Water Culture (DWC) System
In this article, we will walk you through how we built a table top floating raft deep water culture (DWC) system using re-purposed plywood, insulation foam, pondliner, and styrofoam boards on a steel table made from angular bars and steel mesh. Half of the table is set up for circulating Ebb & Flow (Flood & Drain), while the other half is simple Kratky.
For hydroponics growers that have started with Kratky using styrofoam ice chests and have had great success, you quickly realize the limitations of a Kratky system. Scalability of reservoir is a major issue facing Kratky enthusiasts.
The key to a successful floating raft DWC system is to insulate the water reservoir as best as possible to keep water temperature as cool as possible. Also, keep in mind that oxygen should also be available for the plant roots.
We had some left over 3/4″ plywood laying around which we’ve re-purposed as a perimeter frame for our table. The span of the table was close to level, so we did not have to worry about differences in elevation. We settled on cutting the plywood into 4″ inch planks.
To attach the planks to our steel table top, we bore holes and used metal screws. Then we used wood screws to keep the planks firmly attached to each other.
Keeping the water cool is extremely important for an optimal grow system. We had some left over rolls of 10mm double sided insulation material used for roofing that we used as a floor and sidewall insulation. Normally you can use 1″ (or less) styrofoam board but we had some spare parts to up-cycle and re-use.
A simple hot glue gun is an effective adhesive to fix the insulation material onto the sidewalls.
Styrofoam boards normally come in 4ft x 8ft and are easy to customize based on your frame dimensions. Draw the grid lines corresponding to your hole spacing plan. This ensures uniformity and looks better all around. Our hole spacing is 6″ x 6″ inches (center to center).
Using a 2″ hole saw, point the hole saw mandrel to the intersection points of your grid lines. Since our hole saw is only an inch long, we first had to punch a pilot hole through each intersection, then use the hole saw to drill the preliminary hole. Always remember to drill in reverse to get a cleaner cut through the board.
Thereafter, turn the board around and locate the hole and run the hole saw drill through it to get a nice clean 2″ inch hole. Need a hole saw set? Buy it here
We installed a water inlet fixture using 20mm polypipe and 20mm valves & fittings through a 3/4″ hole in the styrofoam board. This is placed downstream from the main filter after the pump to not allow sediments to carry into the water reservoir. The pump is connected to our Smart Socket Switch, which is set on automatic timer to achieve the Ebb & Flow (Flood & Drain) effect.
Now the easiest part of the job is to place seedlings into 2″ net pots. There are many different 2″ net pots, but we tend to like the higher quality ones because they are thicker, more durable, and have a wide lip for better support. Whatever your preference of grow media is, whether cocopeat, vermicast, rockwool, or foam, it will only take a day or two for the roots to settle into its new grow environment.
Filling up the reservoir with the right pH level is important to start the crop cycle. Our table holds about 594L (9.75m x 1.2m x 2″) of water with a 150L waterdrum below for circulation and it took 25mL Phosphoric Acid to drop from 7.8pH to 6.2pH. Make sure to use a quality pH tester that offers reliable readings.
To set your baseline, record the pH, PPM, water temp, and outdoor temp & relative humidity. Log these values into a spreadsheet and take readings daily to monitor fluctuations and observe for any trends that impact your plant growth.