Rain, plumbing issues, and peas, Oh My!

So we had a few issues with our newly filled grow bed. The Bell Siphon valve jammed closed, which resulted in the bed almost overflowing. The valve triggered just in time (no pics alas). In a separate event, last Wednesday, we noticed the bottom tank was leaking, and in response we turned off the pump to avoid the pump running dry. The next morning we turned the pump back on, alarmed that the plants seemed to have suffered considerably overnight from the lack of water. The rain over that night seemed to have done practically nothing to help the plants, and may have even harmed them (see the picture below of the abrasion on the stem). To end this post on an up note, The peas we planted a few weeks ago seem to be doing fairly well!

Current state of the grow bed

These abrasions may be related to the rain we've been having lately

Surprisingly the wind hasn't damaged the peas

Sad tomatoes

Damp earth resulting from the slow leak in the bottom tank

A few videos from the last few days

Behold

Bell siphons are a marriage of witchcraft and plumbing.

It is possible that we need a larger fish tank.

Every day I'm gravellin' - camera ran out of power before capturing Hamish's brilliant wok-spade. 

Done! (Almost)

We finally have a working garden!

Planting things in gravel was a bit of a challenge, since the roots are very fragile, but hopefully they won't mind.

I added a 12V power supply to the electrical box. The pump runs really quiet, and has pretty decent flow. Soon I'll add some electronics to turn the pump off while the bed is draining, and to monitor water levels and temperature.

This is the siphon drain system. It's a bit hard to explain, but basically when  the water reaches the top of the black pipe, the water draining out pulls the water up from the bottom until the water level drops below the slits. The outer pipe below has holes drilled in the bottom, and the other pipe laying on its side is closed on the top.


The system fills up and drains automatically using this system, it takes about 15 minutes to drain. It's pretty cool what you can do with physics!

Here's my good friend Tim helping me fill the grow bed with gravel

Feel free to leave a comment if you have any questions :)
We live in Upper Riccarton, Christchurch if you want to come over and have a look.

We have to wait a few weeks before we fill the lower tank with fish, so stay tuned!

Gravel!

Today we got a trailer load of gravel to fill the grow bed up with:

After that we put the grow bed in its final location, and added the drain pipe

We put an old tarpaulin underneath the plastic to help stop the plastic from puncturing, and to support the gravel better.

The lining of the grow bed

Water Level Prototype

After doing a bit of research, I settled on a capacitive water level probe. It uses an insulated wire that dangles into the tank, which forms one plate of a capacitor. The water forms the other plate of the capacitor, so the capacitance will vary with water height.

The capacitance only varies by a few pF, but it is measurable! The trick is to measure the time it takes for the capacitor to discharge through a 1Mohm resistor:

Here's my prototype test circuit in action, it reads digital 20 for an empty tank, and 40 for about 30cm of water. I should be able to increase the accuracy beyond that.

Aquaponics is a method by which one can eat fish poo without becoming sick