Aquaponics - Loop siphon

Loop siphons are an interesting beast, so I'm going to have a look at them.

I am currently using either a plastic cup scrunched into the gap that I made too small for a proper siphon, or a small glass jar as a bell in my strawberry grow bed. The strawberries are suffering a bit and they don't look as healthy as the strawberry plants I put in the dirt.

We cant have that.

One of the problems with the scrunched plastic cup and small glass jar,was that they make the water level too low for the strawberry plants. What I needed was a normal every day siphon.

I suspect that people tend toward either bell siphons or loop siphons based on which one they got to work first. Now, I know bell siphons are better, but I don't know why I think that, so I built a proper loop siphon.

One that works.

I started with this pile of junk and leftovers from other projects.

A pile of junk is always a good place to start.

And I made this.

I didn't work.

In fact it's kind of difficult to see in this picture, because there really isn't anything that looks like a loop.

The reason I made it like this is because black poly pipe doesn't like to bend.

I suspect I could have made it work by messing about with the flow for a bit longer, but I thought I should make something a bit more conventional because it was, after all, for a blog post.

So I made one that looked like this instead.

Much better.

And it also worked perfectly the first time without any adjustment

It's still not quite conventional because it looks like this from the top.

Which isn't very loopy.

Anyway, it seems to be quite reliable, and I can see no reason why I wouldn't use another one in some future build.


for some reason it isn't as interesting as a bell siphon. For one thing it doesn't make any interesting noises. That could be a plus.


It takes 13 and a half minutes to complete a full flood and drain cycle.

When the grow bed is full, it begins at a trickle and stays that way for a round a minute.

This is the view looking down the media guard when the grow bed is full.

After around a minute it triggers convincingly and starts to empty the bed faster than the water is being pumped into the bed (the pump is run continuously).

Then when the grow bed's water level reaches the height of the outlet pipe, it gulps and burps a few times as it sucks in air and then stops after a minute or so of trying.

This is roughly at the 6 and a half minute mark, so half way through the cycle.

One frequent question is "How long should the flood and drain cycle be?", and after lots of reading and personal experiment, I can confidently say it doesn't matter.

But that's not entirely true.

You don't want your media to dry out, because the plants will die. And as far as over watering goes, you don't want plants that don't like to be too wet (I found strawberries and capsicum plants fall into this category).

So as a guide, I'd say anything between ten minutes and an hour and a half should be ok. aim for something in the middle, and don't care if you are a bit off.

As for loop siphons, a few things to remember are...

* don't make your loop too big because the pipe needs to seal with water to become a siphon, and a long gentle curve seems to work better. The longer it is, the less it will trigger in a nice decicive way. It will probably still work, but if your loop siphon is making lots of false starts it might need the loop to be tightened a bit. Mine loop is around 20cm in diameter, which is about as tight as garden hose likes to be bent.

*There is a range of flow at which a siphon will both trigger, and also stop. To make a siphon easy to calibrate, just add a tap to the water going into the grow bed. If it doesn't start, you need more flow. (or reduce the diameter of the loop tube), it it doesn't stop, you need less flow (or increase the size of the loop tube's diameter).

*Remember that if you have more than one grow bed, any adjustment to how much water you direct into one grow bed, will probably effect how much is going to the other.

To get around this you can put a tap on a T junction so that, rather than the tap adjusting how much water goes into the grow bed directly, it adjusts how much water you divert back to the container where the pump is.

This is a good idea for any style of siphon if you have more than one grow bed.

The water that goes back to the sum just adds aeration to the water, so it isn't wasted.

Another use for the diverted water might be to feed a constant flood growbed, where the amount of water can vary without concern.

*It seems that the siphon triggers more decisively when the exit end is pointing straight down. The direction or angle of the entry end of the loop didn't seem to make any difference in my experiments.

My 500ml jug took 11.3 second to fill at the hose bringing water to the grow bed, and 5.1 seconds to fill at the pipe draining water out of the grow bed.

My siphon's loop is made from 12mm (internal) garden hose.

I don't think there is a lot of difference between a bell siphon, and a loop siphon. In future, I'll be using whichever one I feel like making at the time.

The only disadvantage I can think of is that if you were making a very large diameter on, the loop might be difficult to make because big pipe tends to be thick pipe, and think pipe doesn't like to bend. You could probably scale the loop up to any size, but the loop might take up a lot of space. A Bell siphon can be scaled up to any size and not take up a lot of space.

Advantages include that with a loop siphon, you can adjust your water depth in a grow bed simply by repositioning your loop a little higher (the top of the loop sets the grow bed water height), and a loop siphon is probably a bit cheaper to make.

120 Things in 20 years changed it's mind about loop siphons in aquaponics.


  1. What about a U bend siphon made with PVC pipe? Any differences to a loop siphon?

  2. I'm not really sure what you have in mind, but all siphons effectively work the same way. But keep in mind, the second photo shows one that didn't work but that looks very similar in design as the one that does.

    But like I said. They all work the same.

    Unless you email that guy who successfully challenged the dictionary definition that's been used for the word "siphon" for the last hundred years.

    Then you will be just left scratching your head in wonder as you discover discover that academics aren't always. Sometimes they can see something's wrong, but have no idea what's right.

  3. One good thing about PVC is that you can easily test it to see if it works. It's just so easy to work with.

  4. This comment has been removed by a blog administrator.

  5. Sorry op... your shit's a fraud so it had to go

    for better spamming, try not starting all your posts with...

    "Aquaponics is a method by which you grow plants and nurture aquatic animals together in a system that "

    Mix it up a little.


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