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Le rôle du siphon en aquaponie

The role of the siphon in aquaponics

In this article, we will see in detail the usefulness of the siphon in aquaponics: what it is for, how it works, how to solve problems related to its operation, etc.

What is a siphon used for?

A siphon makes it possible to obtain tides in the culture tank, this is its primary function. No siphon, no tide (note that there are different types of siphon such as the bell siphon).

Allows to have a huge supply of oxygen for the plants via the roots and also for the bacteria. This tide will therefore bring them all the necessary oxygen.

Another function of the siphon or perhaps a side effect is that it will prevent the accumulation of organic matter: dead roots, leaves... Anything that will clog your tank.

And finally, we must note a very important thing, it is that the siphon is mechanical. You absolutely must have a pump. Generally, this is already the case when it comes to an aquaponic system.

How it works?

First, you must have your bin installed. Once you have your bin, we will place the siphon. You will have a tube, which will determine the maximum height of the water, it is generally the top one. Thus, the water will rise in the tray and then flow through this tube. You will also have two 90 elbows, this will allow the water to return to the fish. Above this evacuation tube will be placed the bell. That's why it's called a bell siphon. It is thanks to this bell that we will be able to obtain a siphon. We will then add a protective cylinder to prevent the media from entering the bell or the evacuation tube. So your clay pebbles, pozzolan, etc. must stay in the grow tray and not clog the siphon.

How's it going?

The pump that is placed in the fish tank will bring the water. Little by little, the culture tray will fill up and the water will then rise. Once the water has reached the height of the discharge pipe, it will descend in this accelerated pipe and this acceleration will create a depression. It is thanks to this depression that all the water in the tank will be sucked into the drain pipe. This is called a siphon.


Some useful tips

First of all, you should know that the sizing of the siphon is empirical in terms of the width of the pipe and in relation to the size of your tank. In short, you will have to apply the double rule, that is to say that the cylinder which protects the bell will have a diameter which is twice the bell and must also be able to let your hand pass (this is important for servicing). The diameter of the bell itself will be twice the diameter of the discharge pipe. So if you have a pipe that is 3.2 cm, that will give us 6.4 for the bell and 12.8 for the protection cylinder.

Second, since this is empirical, you will set up your system and then test it empty without putting any media or plants in it. Once the siphon starts and stops, you can add your media, your clay pebbles, your pozzolan and test again before putting the plants in.

Third, for the water drainage part in the fish tank, you will need two 90 degree angles. This will allow you to correctly reprime your siphon, which is very important. You will need to set your pump flow so that there are approximately three to four tides per hour, i.e. every hour your water must have risen three or four times and fallen three or four times.

Fourthly, you must ensure that you can control the flow of water that arrives and for this, it is strongly recommended to add a valve. Often, it is easier to have a valve at the inlet of the culture tank rather than having to modify the flow rate directly on the pump.

And finally, as aquaponics is a living system, you will inevitably have roots that will clog your siphon at some point. You should therefore check regularly by putting your hand inside the protection cylinder.

The most common problems encountered with a siphon and the solutions

There are two styles of problems:

  1. The first is that the siphon does not start,
  2. The second, the siphon starts but does not stop.

Why does the siphon not start?

It is said that the siphon does not start when the water rises in the pan, comes to the top of the drain pipe, flows out, but is not sucked up. It's like you don't have any bells. The water level remains constant and therefore obviously there is no tide. The first thing to do in this case is to check that nothing is obstructing the bottom of the bell and the bell protection.

Indeed, at this level, if ever you have clay balls or sand that have come to get a little on it, or if your bottom is not completely flat, then you will have problems. It is also necessary to check the tightness of the bell and particularly the part of the top. Often these are DIY systems, so there is the main tube and over it there will be a cap. And if it is not waterproof, the bell will not be able to play its role.

Finally, if the water flow is too low, that is to say that if the tide rises very slowly when it reaches the top of the discharge pipe, it will evacuate very slowly and will not create any 'acceleration. The siphon will therefore not engage.

Second problem: the siphon starts but does not stop

This means that all the water in the tank is sucked up, but the siphon does not defuse and the water remains at the bottom. This type of problem is more painful than the first because suddenly, your roots which were in marshes will find themselves in the air.

Three reasons can be the cause:

  1. Check that the drain at the level of the fish tank is not in the water. We must not forget that we must regularly add water to our aquaponics tank because the plants sweat. So at some point, you may have added water, not been careful, and the last 90 bend in the drain pipe was left in the water. In this case, the siphon will not stop.

  2. The second thing that can give you trouble is the exhaust configuration. Let's say for example that you see that there is a first 90 bend, a tube and a second 90 bend depending on the length of the pipe depending on the dimensions of your tank. You may have siphon problems that do not stop.

  3. And finally, the last cause can be the water flow which is too high. The siphon is triggered, the tank empties, but then the pump brings so much water in relation to the evacuation speed of the siphon that the air cannot enter and the siphon does not defuse. We're going to have a siphon that doesn't stop and water that stays down. In this case, we are going to reprime the siphon by hand by lifting the bell, that is, we are going to put our hand inside the protection cylinder and then lift the bell. We are going to turn it around a little, put it back, and try to solve the problem by looking at the causes mentioned above.
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