Ebb and flow systems

There are several methods to create an ebb and flow cycle in your system. One of the simplest is to purchase a programmable timer to hook up to your pump. Assuming you plumb the system such that the water flows into the grow bed from the bottom, the timer will cause the grow bed to fill when the pump is active and the water will trickle back through the pump and into your fish tank when the pump is not active. The down side is that timers can be expensive and adds a bit of technology into the mix. The up side is they are pretty darned reliable and easy to use.

One thing to note with timers is that you will need to put some sort of overflow/outflow mechanism to prevent over filling. The water needs to have a path to drain back into your fish tank at the maximum height of your grow bed so that even if the pump keeps running you will  not overflow the sides of the bed.

Bell siphons are another low tech way to implement an ebb and flow cycle. Basically all a bell siphon consists of is a small pipe that sticks up from your main outlet and is cut off just below the maximum height you want your water level. A larger pipe with holes in the bottom to allow water in is placed over the smaller pipe. When the water level reaches the top of the outflow pipe it will begin to spill over and create a suction. This suction will be maintained until the water level falls below the holes in the outer pipe and the suction is broken. The cycle then starts over again.

A couple of items of note:

Bell siphons generally work best if you "neck down" the bottom outflow pipe to a much smaller diameter pipe. The reason for this is that you need to keep the outflow pipe completely at capacity otherwise the suction will break more easily. So... if the top of the outflow is larger around than the bottom there won't be a problem keeping the smaller pipe at the bottom supplied with sufficient flow to keep it full.

Also, you need to make sure that your inflow is *less* than the capacity of your outflow pipe. If you are putting more water in than can drain out the bell siphon your grow bed will never empty so it can't complete the cycle.

In short... the bell siphon is a bit of a balancing act, but IMHO well worth the effort.

Here are some illustrations:

Ok... so some of y'all might have noticed that in the above video the pipes on the bottom of my outflow are the same diameter as the top part that controls the maximum water level. While this works, I found from trial and error after filming this that reducing the bottom part of the outflow to a considerably smaller size was much more trouble free.

So... there you have it...

Enjoy!