Flood and Drain Systems are probably the most common types of aquaponics systems used by hobbyist. Human ingenuity has provided us with as many different styles of aquaponics system as can be imagined. Many are tweaks of tried and true systems created by those seeking a bit more efficiency or a boost in productivity. There is no way we can look at every possibility of the varied takes on system design. Therefore we have to stick with the basic concepts and genres.
The most basic is the flood and drain system, and at its most basic it consists of a single grow bed and a fish tank, arranged so that the water is pumped to the growbed. The grow bed is situated so that the water flows directly back into the fish tank. A simple and elegant solution.
The key is in the descriptive name of these systems; flood and drain. The goal is to build a system that alternately fills the growbed to a predetermined level with water and then empties that water back to the fish tank. Hence, flood and drain. This flood and drain cycle can be achieved in several ways. Systems have been built and successfully operated using float valves, electric timers, electro-mechanical valving systems and siphons of various sorts
Our goal is to keep things simple, so our first alternative is to employ a siphon system. Even with this decision, there are almost as many options.
A siphon in any form is perhaps the easiest means of operating a flood and drain system. It can be mounted internally to the grow bed or externally. Its name is descriptive; the entire thing consists of a loop of tubing. These are easy for the home DIY’er to construct and install. They need not be made of flexible tubing. They can be constructed from PVC just as easily with a few 90-degree fittings.
Loops siphons can be arranged to make adjusting the water level in your growbed as easy as changing the top level of the loop on your siphon. As you can see in the illustrations, almost any material can be used to construct a loop siphon, even a length of old garden hose.
There are a few cautions to be observed. If you are using clear tubing, you should keep the loop siphon out of sunlight as much as possible. Clear tubing will grow brittle and hard and eventually crack due to UV exposure. It will also grow algae which can eventually clog or impede the flow of water through the tubing, making the operation of the loop inconsistent.
One other consideration is the size of tubing selected. A good rule of thumb is to use tubing a bit larger in the inside diameter than the pipe delivering water to your growbed. The will allow the growbed to drain faster than it fills, a much-desired design feature that will be discussed in detail later.
The second option when considering siphons is a bell siphon. Bell siphons are a bit more complicated, require more parts and a higher level of buildability. They can also be harder to fine-tune so that they operate consistently and properly.
Bell Siphons consists of several parts, a guard that keeps your grow media from leaving the tank with the water, a standpipe and a siphon bell. The bell siphon operated inside the grow bed with the media surrounding it. It requires an opening in the bottom of the grows bed for the drain tube.
Building and installing bell siphons is almost a study in and of itself. There are thousands of pages of discussion, diagrams, and data about bell siphons in aquaponics systems on the web. Because of this, building and installing a bell siphon is almost as much of an art as it is a science. We will take a much more in-depth look at bell siphons, how they operate, the considerations one should make when planning one, design options, and the necessary calculations that are made before starting your build. We will devote at least one chapter to bell siphons later in this series of articles.
The great thing about bell siphons is when they are properly sized and constructed they are almost bulletproof. They do require a certain amount of maintenance and care, but they will operate consistently for long periods with very little attention.
Mechanical control systems fall into two categories, both of which depend on some interruption in the water flow to allow the grow bed to drain. Interrupting the water flow is accomplished in several ways; the most common depending on timers to start and stop the flow of water or mechanical valves to actuate the draining process.
The most common type of electrically controlled grow bed uses a timer to stop and start the pump at predetermined intervals, which allows the growbed time to drain. Timed pump systems use a standpipe with a weep hole near the bottom. The timer starts the pump, and it runs long enough for the growbed to fill to the level of the top of the standpipe. When the timer stops the pump, the water continues to drain through the weep hole at the bottom of the standpipe. The smaller size of the weep hole allows the pump to fill the growbed and then allows the water to drain slowly from the grow media.
These systems are very effective in large grow media troughs and can be effective in commercial operations. Siphons are hard to manage in large grow areas where more than one drain would be needed. Timed pump operations with multiple weep hole drains work well. Also, they are simple to build and inexpensive.
The downside to timed pump systems is that if the timer fails, the plants can be left without sufficient water and can suffer quickly. Like any mechanical device, they require attention, maintenance, and replacement.
We will take an in-depth look at timed flood and drain systems in a later article.
Mechanically controlled systems usually involve some sort of mechanical valve arrangement that either controls the flow of water into the grow bed or opens a valve to let the water drain. Either way, there are so many disadvantages that very few systems work on this kind of arrangement. Solenoid valves are notoriously maintenance-intensive, especially in a damp or humid environment. Building such a system can be expensive and involves not just running lines for water, but electrical and control lines. Not the usual DIY’er affair.
We will look at some arrangements for mechanical controls, but we won’t spend a lot of time on them. For most operators, they are just not feasible.
For the DIY’er and hobbyist, keeping things simple is your best option. That is why we advocate a flood and drain system in a media-filled bed run with a bell siphon.
In our next article, we will look at the mechanics of other systems such as raft systems and nutrient film technology systems.