The Grow Beds

The grow beds are assembled from 2 x 12 pressure treated boards framed into boxes 23" x 23" with a 3/4" pressure treated plywood base.  A single 1-1/2" hole is bored through the bottom for the bell siphon to drain through.  I found a threaded PVC bulkhead fitting that I used to plumb through the drain hole.

 Standard Bulkhead fittings (shown as a test fit).  These were installed after the liner was installed.

Each of the grow beds are lined with the same pond liner that we used for the pond.  It is simply folded neatly down inside of the grow bed box and stapled into place.

I used standard pond liner from Loews.  I cut sections from the larger sheet ahead of time shown below.

Next I neatly tucked and folded the liner into the box (holding it in place with a brick)

 Folding is an art.  Practice this a lot before final stapling

Finished Box ready for a bulkhead fitting

We used bell siphons to drain the beds.  They seemed like a simple method.  These are the basic dimensions of the PVC piles that I cut to make the bell siphons.  

1. The smallest one is the stand pipe.
2. The middle one is the bell siphon.
3. The large one is the gravel guard.

We had to trim the stand pipe to the finish length in order to set the water depth of the grow beds.  Also some fine tuning will need to be done after you have established your flow rate into the grow beds.  In my case (and everyone will be different) I needed to wrap a couple layers of tape around the top of the stand pipe (to make the diameter a little larger) so that the bed would flush properly as the ratio between the Stand Pipe diameter and the inside diameter of the bell siphon is critical for proper function.

Here the grow beds are being installed on top of the heavy duty frame that I built.  These beds will be very heavy and need adequate support.

 Above:  Shows the 6" diameter drain pipe dumping into the pond

Below:  Shows the Grow beds filled with Pea Stone.  There is a lot of conflicting information regarding the type of media to use.  We chose the pea stone for cost and convenience.  So far its working very well but we did have a bit of a pH problem.  Read on to see how that was solved.

Above is a schematic of the water flow

prior to putting the stone into the grow beds, Lorraine washed all of the stone to get the dirt off.  We did not want to muddy up the pond after all of our hard work.

The next photos show the drain system.  The drain pipes need to step down in diameter and need a change in direction in order to create some back pressure for the bell siphons.

They then drain into a large 4" pipe that will handle the flow if all of the beds drain at the same time.

The pump that we used is a 850 gallons per hour unit that we found on-line.  it feeds the single pipe running up the back corner of the green house and flows water into a 4" pipe that we use in a Hydroponic fashion.  The water then drains out the far end of the hydroponic pipe down into a manifold where 5 separate outlets fill the grow beds.  There is a bypass on the end of the manifold so that we can throttle the flow rate.

I read somewhere that you only should have one pump.

"One Life - One God - One Pump"

 In the picture below, you can see the large drain pipe dumping back into the pond.

We used 3/8" pea stone for the grow beds due to the low cost.  The system was designed to handle the weight and all of the stone needed to be washed off prior to filling the grow beds.  We ran into a small problem while we were waiting for the system to balance.  The pH remained high (8.0 to 8.5), we did some research and discovered two things.

1. The pH of our tap water is 8.1
2. The pea gravel is leaching out a bit of limestone.  Not a lot, but a little.

We did a test where you pour some white vinegar into a glass of pea stone and see if it fizzes (or bubbles).  When we did this we noticed a very small amount of bubbles forming on the stones but not a fizz.

To lower the pH we started the system on a regiment of Muriatic Acid.  We picked up a 1 gallon container at a Box store.  You cannot make rapid changes to the system of the fish might die so we began adding 2 table spoons per day (diluted in a cup of water).  We did this for three weeks and the pH has dropped to 7.7 and the plants have begun to look better and grow more rapidly.