A Compact Shelf Size No-Leak Ebb & Flow System

I like ebb and flow systems, but I wish they were more compact. So I set out to design an ebb and flow system that would fit comfortably on a shelf. I began with two Sterlite 10-gallon totes. Each is 25-3/4” x 18-3/8” x 7-1/8”. I determined to stack them and use the  bottom as the reservoir and the top, filled with LECA, for growing. I wanted them easy to take apart and clean and essentially free from leaks. 

 

The theory of operation in this type of ebb and flow is that the timer turns on a small pump that fills the growing tray through a connector that has a grill protecting it from clay pebbles dropping in. An adjustable riser is set to the desired nutrient depth. Nutrient is pumped up and continuously overflows through the riser and returns to the reservoir. At the end of the timed flood period, the pump stops, and most of the nutrient drains back passively through the pump. A small quantity of nutrient remains, but that is on no consequence. It may actually protect the roots in the event of a pump failure that is not discovered promptly.

In the lid of the lower tote, the reservoir, I made a 2-inch hole in the lid near one end. 

This would be to inspect and service nutrient. The top, then, could sit back far enough to clear this port. I leveled it using 1” Styrofoam.

In the growing tray, I mounted a set of common ebb and flow fixtures, a riser to set depth and a fill and drain connection. These pass through the bottom of the tank. The pump was connected directly to the drain and fill connector with ½” vinyl tubing which fit both the connector and the pump discharge. When held aloft, the pump hangs below the growing tray.

First, I drilled the holes for the ebb & flow kit. 

Then I set the growing tray in place on the reservoir lid and marked the center of the ebb & flow kit holes. 

I installed the kit.

I then made two holes in the reservoir lid. A large hole to accept the pump. And a smaller hole where the overflow riser would drain back into the reservoir. 

I used a 25 watt pump rated at about 500 GPH. This pump did not have such high flow that it could get ahead of the depth riser. If it had, other steps would have been required to limit the flow, but it turned out that the fact that these magnetic drive pumps are capable of very little pressure worked to my advantage. The increasing back-pressure of the nutrient filling the grow tray progressively slowed the flow with the pump intake adjustment near minimum until it was circulating fresh nutrient but draining the overflow just about as I wished.

In my larger ebb and flow trays, I had used an 800GPH pump moving nutrient up from the floor, and I had to use a ball valve to prevent the flow from overrunning the riser and flooding out of the tray.

Some shimming with the foam was required to allow the pump to rest on the bottom of the reservoir and to level the growing tray.

 Depending on your pump size, the tubing may have to be adjusted for length. When level, there were foam shims at front and back between the grow tray and the reservoir. 

 

One nice feature is that, because the reservoir lid is recessed, any leaks at the riser and fill connectors will just collect in the lid and drain back through the service port. The service port is made lightproof using a 2” net cup with a clone collar. The fit is loose enough that leaks can drain into it. The pump power cord can just run under the edge of the lid. So, there are no holes in the body of the reservoir. There have not been any leaks, but because of this arrangement, they cannot escape the reservoir lid.

 I filled the grow tray with LECA just beyond the point where the depth riser would be draining the overflow. 

A test run with water showed that it maintained that depth during the fifteen-minute flood period. 

 

I then added another layer of LECA. This layer is above the flood and stays dry and therefore does not grow algae. 

 

I added nutrient and set the timer to flood for fifteen minutes every three hours. I have learned that beyond three hours, LECA begins to dry, and I want it to retain moisture to protect roots. I left it to cycle that night. The next day, I adjusted pH and planted shallots in one tray and mixed day neutral onions in another. The third will be an experiment in carrots, using Parisienne/Nantes carrots which are ball shaped and hopefully will not be so sensitive to the medium characteristics that caused regular carrots to twist into knots. 

 

The finished unit is about 34” x 18” and about 15” tall. That brings the tops to a good working height under the lights, which supplement the natural light in the greenhouse with its heavily matted clear panels.