Backyard Aquaponics
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Hello,

I need to build a bell siphon and an aquarium for a 50 cm (L) x 30 cm (W) x 30 cm (gravel depth) grow bed.

The parts of the system are described in this link, which I will follow after adjusting the described dimensions:

https://www.instructables.com/id/Make-a-Bell-Siphon/

So:

1) what should be the height and the diameter of the PVC pipe of the Gravel Guard?

2) what should be the height and the diameter of the PVC pipe of the Bell Dome?

3) what should be the height and the diameter of the PVC pipe of the Bell Siphon?

4) what should be the diameter of the drain pipe?

In addition:

5) Is the adapter on the top of the bell siphon, as shown in the link, really useful or necessary?

6) how much water should I put in the aquarium for that system?

7) can you suggest me a good electric pump for this system?

thanks.

Hi Esperoit,

The bell siphon is a useful device for flood and drain. The exact size of parts isn't important, rather that they are all appropriately sized in relation to each-other and in relation to the flow rate of the pump/rising water level in the GB.

I will try to answer your questions in order.

1. The top of the gravel guard should be a couple of inches above the level of your media. It's annoying when media falls in there!

2. the top of the bell dome should be a couple of centimeters above the top of the standpipe tube which sits inside it. Similarly, the tube should be a centimeter or so wider than the standpipe inside it, for me at least, this was the "next size up" in standard PVC tubing.

3. The inner siphon tube/standpipe, will determine high-water level, so should be a couple of inches below the surface of the media. 3/4 inch as in the diagram you provided will be good. Basically, just get three sections of tubing in three consecutive sizes, the widest, your media guard, should be around the width of a 1.5 lt drinking water bottle, and the narrowest, you bell siphon inner tube, should be roughly the width of the cardboard tube from a roll of aluminum foil. And the bell dome tube should be in-between the other two.

4. The drain pipe can be the same diameter as the siphon tube, or possibly slightly narrower, definitely not wider. Having the drain pipe taper towards the end can help, mine is flattened which works well.

5. The adapter at the top is possibly not necessary, but this depends on your water flow. It is a very good idea to include it as the siphoning action will be initiated much more effectively, enabling you to use lower flow rates and less power pumping water.

6. As much water as you want to. Is your system just an aquarium and a grow bed? If so you need to bare in mind the varying water level in the aquarium. Your grow bed sounds very slightly bigger than mine and my aquarium is 150 lt. In my system the variation of the water level is very small. I believe with a fish tank of 100 lt and above your system would be fine.

7. An aquarium submersible pump, like the one shown in your link. You must look at the spec of the pump, it has two key pieces of info: head height and flow rate. They often include a graph showing the pump's flow rate at varying head heights. Make sure the head height is in excess of the height you intend to pump to. If you haven't built the system yet try to keep head height low to save energy. It's generally recommended in aquaponics to turn over the fish-tank volume every hour, but the importance of this depends on your stocking density and fish species' sensitivity etc, for (understocked) aquarium systems this is probably of less significance.

I have a 7W pump which claims a flow rate of 600 lt per hour and a head height of 115 cm. I pump to a height of around 50-70 cm, to a grow-bed of approximately 50 x 20 x 20 cm, and my siphon took some tinkering, and sometimes needs fine-tuning but works well on the whole. I would recommend you buy a pump of at least the same power as mine or more, and if you haven't built your system yet, keep head height below 50 cm. Buy a pump which prioritizes head height over flow rate, some do the opposite.

Finally, with regards to point 6. The number of fish you can have is determined by the amount of wet media in your system, this is regardless of whether your aquarium is 100 lt, 500 lt or 1000 lt. You can search this ratio, it's explained in many threads here.

Hello Danny,

thanks for your reply.

1) Can you tell me if all the sizes of the instructables are correct or I have do modify some of them? In case I have to modify them, can you write a more precise size for the diameter of the a) siphon b) dome c) guard

2) More specifically, the bell siphon's height proposed in instructables is 6'' ( = 15cm) long, not 3/4''. Then, given that the gravel depth is 30cm, the high-water level will be at the middle of the gravel depth. Is this correct or do I have to use another height? You wrote that "it should be a couple of inches below the surface of the media", but this is not 15cm below a gravel depth of 30cm.

3) I know that the main application of the bell siphon is to avoid to rot the roots of the plants. So, as soon as the water reaches the high-water level, it is drained fast by the siphon. Then, if you write that the high-water level should be a couple of inches below the surface of the media I deduce that this should be (more or less) the roots depth too... is this correct?

4) how can I tune and check if the bell siphon do works, after making it? Should I remove the gravel from the tank, fill the tank and see if the siphon drains fast the water when the high-level is reached ?

Ah, yes i meant 3/4 inch tube diameter, not height.


1. In terms of the instructables diagram , the figures are good for tube diameters.

2. 30 cm is a good gravel height, 25 cm is a good bell siphon/high-water level. Less would be a waste (only wet media biofilters) and more could cause issues.

3. Yes, when planting you want at least some of the roots at a dept greater than 2 inches, so they are regularly submerged in water. However, capillary action will also bring the humidity higher than the high-water level, how much depends on the media used, expanded clay will be moist at an inch above the high-water level. Seeds can be germinated by scattering directly into grow beds thanks to moisture from capillary action.

4. I'm not sure I understand what you mean by removing gravel from tank?.. A bell siphon with no adaptor and no right angle on the drain pipe will work with a high enough flow rate. First you should build it (including adaptor and right angle), then test it. Determine the minimum flow rate needed to initiate the siphon. If you buy a pump that can provide that flow rate, your siphon will DEFINITELY work, as the water level will rise significantly faster when its full of gravel.

I would suggest not including the final downward angle piece on the drain-pipe in the indestructible diagram. Instead use boiling water to flatten and bend the tube downwards. This will help create the siphon action quicker and will enable you to use lower flow rates and less pump power.

5) The adapter (I believe) makes triggering the siphon action easier.

Additionally, install a ball valve at the water input to your growbed so you can control/adjust the flow. Too little flow and the siphon won't start, too much and it won't stop.

Thanks for the explanation.
So, after I have made the siphon with all the sizes we just discussed, do I only have to tune flow rate of the input water (I could use a ball valve as arbe suggested)?
Or do I have to tune/adjust the sizes of the components too?
Changing the sizes of the components would be hard, after they are made...

I think Arbe's suggestion for a ball valve is good for larger systems, but for a small-scale aquarium system it might not be effective or necessary.

Most submersible pumps come with a flow adjusters, so you can set the rate accordingly. There will be no need to adjust the tube sizes or replace any parts etc.

A couple of final adjustments can always be made if needed such as flattening the drain pipe, mine even has a small stone inside it which helps create the siphon, but I imagine that if you keep head height below 50 cm and get a pump of 7W or more none of that will be necessary.

Remember, flow rate need not be precise; as long as its fast enough to initiate the siphon and slow enough for the siphon to break it will work fine. If you build it as we have discussed this will be easy to achieve!

Thanks for all the answers.
One last question: if the bell siphon's height is 25 cm , which should be the height of the bell dome? The instructables link says that it should be 4'' higher, which means 35 cm but it seems too high for me...

4" sounds way to high. I would think 1" or even slightly less would be ok.

Thanks.

What about the holes around the tubes, instead of the cuts, as proposed in the instructable's link?

https://cdn.instructables.com/FIE/KQ6Y/ ... .LARGE.jpg

The holes are much easier for me to make, with a drill, but I wonder if they do work...

The link in your first post shows a Gravel guard and a Bell with holes that are unsuitable too small and not enough

The Gravel guard needs plenty of holes or it will restrict flow and you will have trouble getting the siphon to start and stop , and plant roots will quickly clog it up , growbed will fill and overflow water onto the ground.

Guards need regular turning to cut roots off , push down hard and turn the guard

The Bell needs large holes as well to work properly , start your holes up the bell a bit , if you cut notches on the bottom or take the holes right down to the base the bell will keep sucking up the sediment off the bottom of the growbeds and your water wont clear.

I wasn't going to chime in, but I've got some time on my hands this arvo, so for what it's worth, here goes...

(1). If the top of the siphon kit is open, then it should probs be at least about 25-30mm taller than the depth of the gravel. If you make it as per the siphon kit in the pic below, you can make the gravel guard just a few mm taller than the gravel... Nice and neat.

If you do want to make it as per the one in the pic below, the inside diameter (I.D.) of the gravel guard should be just a few mm more than the outside diameter (O.D.) of the bell pipe cap. This stops gravel or debri entering the siphon, but will still leave plenty of room for water flow between the guard and bell.

(2). The I.D. of the pipe used for the bell should be somewhere between 2x to 3x the O.D. of the standpipe. If the tolerance between these two is too narrow, or too large, it makes the siphon less reliable.

As far as the air gap between the top of the standpipe and underside of the bell cap is concerned, a well designed siphon will work with a very wide range of sizes here. However, if you make it too close it can make the siphon very unreliable. Most of my siphon kits have around a 50mm air gap.

(3). Unsure of what you're asking here.

(4). For your GB volume of 45 litres I would use 15mm PVC for the standpipe, any larger and the in-flow required into the GB to get the siphon working properly, as well as the duration of the F&D cycles, will be so rapid that the fines will never settle out and your system water will become increasingly turbid and full of organics.

Even with a 15mm standpipe you'll probably find your F&D cycles will be as frequent as 4-5 minutes with the GB in-flow tuned properly. With a 20mm (3/4") standpipe it would require around twice the in-flow and the F&D cycles rates will be halved. The standpipe in the pic below is 15mm and I recommend that for GB's of 50-200L capacity, but there is really no smaller option as far as pipe is concerned.

(5). Nope!... I've done plenty of testing of siphon kits over the years and I don't bother with the inverted reducer atop the standpipe, it's not required.

(6). A gravel:water ratio of 1:1 would normally be recommended, but with system that small you'd probs want more water. I make a single barrel system with a 45L GB capacity and 70L FT water capacity and it works well with half a dozen goldfish.

(7). Provided there isn't too much head, I'd recommend a 750Lph pump, such as the Aquapro AP750, and you'd still have plenty of flow left over to run through a spray bar, which will also help with tuning the flow to the GB without putting back pressure on the pump. Depending on the situation (ie: very little head height) you could possibly even get away with a pump as small as 550Lph, such as the Aquapro AP550 or similar (Don't know what brands you have access to over there).

Another tip, as others have mentioned, do away with the second 90 deg' elbow in the return line. To get the back pressure required for the siphon to work well, all you need is the one elbow followed by a horizontal pipe with a length about 6x the diameter of the pipe.

Also, don't have the water inlet holes/slots at the base of the bell. If you place them about an inch up from the base the siphon will shut off more reliably and you won't constantly be dragging crap from your GB back into your FT, as Terra mentioned.

As far as slots v's holes in the gravel guard is concerned. The gravel, especially expanded clay beads, can settle into the holes, blocking or reducing water flow.

Finally, the number one rule for designing/building a reliable siphon kit... Observe the K.I.S.S. principle.

P.S. That design you linked to, I don't know who they are, but I would suggest they haven't made and/or trialled many bell siphons. Take any info or advice they give with a grain of salt.
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I'm about to transition my GB to bell siphon, so I appreciate the ongoing answers to questions and guidance in this thread!

I love the top on your media guard Mr. Damage, it looks the goods

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