DIY Bell Siphon for Ebb and Flow Aquaponics with 75 gallon Aquarium

I had a rough week this last week, so I decided I needed to build something. So I built a bell siphon for an ebb and flow grow bed (also called Flood and Drain grow bed_ for the 75 gallon fish tank in the living room. This will allow me to grow plants using the fish water. This is pretty cool, as it means that the plants will remove the nitrate buildup which is the primary reason people need to do partial water changed in their aquariums.

My 75 gallon aquarium in the living room before I added the  aquaponics component to it.
My 75 gallon aquarium in the living room before I added the aquaponics component to it.

The whole thing will be completely automated and cost me less then $50 including buying tools and leaves me with lots of spare parts. 3 pieces of 4 foot PVC pipe with only about 6 inches cut off of each, so I have enough of this to make half a dozen more if I wanted.

A bell siphon is a passive autosiphon device that allows a continuous flow of water into a container to periodically be drained completely out of the container. This is good because it allows me to have my Eheim aquarium canister filter output into the grow bed, and the bell siphon will flush the bed regularly, aerating the plant roots.

To start, I assembled a drain out of plumbing PVC parts. This consists of a stand pipe to go inside the aquarium, 2 fittings to work as a bulkhead nipple, and an offset to route the water around the aquarium lid into the drain tube.

Showing where the tub will go.
Showing where the tub will go.

My wife let me buy the parts and take over the 75 gallon aquarium in the living room with my plants. She had it decorated really nicely, but my plant stand was evicted from its spot to make space in the baby room. They needed a place to go, and I used this as an excuse to work on the aquaponics setup.

Katie and Bella Supervising
Katie and Bella Supervising

I started fiddling with the pieces I had bought and realized that I didn’t get all the right pieces I wanted, but I had gotten enough to make it work.

The bottom half of the bulkhead and the 90 degree angle.
The bottom half of the bulkhead and the 90 degree angle. The angle will provide the offset to go around the tank lid.
A bit of glue oozing into the PVC joint.
A bit of glue oozing into the joint. This needs to be cleaned out to provide less water flow resistance.

I used an antique brace with an adjustable size bit to cut the hole in the plastic. Basically, the edge of the bit would score the plastic. It worked great, except for the plastic cracking.  I siliconed it up, but, to my great annoyance, the silicone was old and didn’t set. I had to clean it off and go get a new tube and try again.

Cracked grow bed bottom
Oohps! I cracked the bottom of the grow bed. No worries, a bit of silicone will fix it right up!

After two days of futzing with this thing, I finally got a dried silicone seal around the stand pipe and over the crack. The grow bed will sit on top of my 75 gallon aquarium so I designed the drain to offset around the aquarium lid. No drilling holes in the lid… yet…

The stand pipe drain for the ebb and flow hydroponics grow bed.
The stand pipe drain assembled and ready to seal in place with silicone

I then made the bell siphon which sets over the stand pipe. I again used my brace and a smaller bit to drill holes in the 3″ PVC pipe. This made it much easier to cut with the PVC cutters I had bought. The 3 inch was just to thick for me to cut otherwise.

PVC holes drilled with a brace and bit
Using a brace and bit to drill holes in the PVC where I will cut it to make the bell siphon.
The bottom of the bell siphon
The notches in the bottom of the bell siphon allows water to flow in easily.

A slight design flaw (um, the drain) left me with a grow bed that wouldn’t sit on the aquarium stand lid. A bit of scrounging around, and I found a plastic crate that I am using. The grow bed sits on the crate, which leaves enough room underneath for the drain to fit. It looks a little precarious, and I would like it to be the 4-5 inches lower, but it works for now.

The aquaponics ebb and flow growbed sitting on the aquarium light hood
The grow bed sitting on the aquarium light hood.
Aquarium filter filling the aquaponics ebb and flow growbed on top of the light hood
The canister filter has nearly filled the growbed. The water height is limited by the height of the stand pipe.
The bell siphon sitting on top of the stand pipe
The bell siphon sitting on top of the stand pipe. This is where the magic happens.
The bell siphon sitting on top of the stand pipe
Looking at the whole bell siphon drain.
Threaded drain gives me options in the future.
The threaded bottom allows me to potentially change how I drain this grow bed if I wanted to.


The growbed is continuously filled, and intermittently dumps into the aquarium below.

The drain in the aquarium
The water from the grow bed returns back to the aquarium here. The grow bed is still filling in this photo.
Bell Siphon draining into the aquarium
Bell Siphon draining into the aquarium. See all the water flowing out?

I placed my plants around the grow bed and the few items that where required to stay on the tank stand – family photos. I think it looks pretty good in the house! I hope to grow lettuces and herbs such as basil in it. Things that we eat regularly and are best fresh.

Indoor aquaponics setup on top of a fish tank
I only have desk lights with CFL bulbs right now. I think it looks pretty good!
Living Room Aquaponics in an aquarium
The tank looks good with the aquaponics on top!
I am pretty sure I can’t feed everybody in the photos… yet…



You can visit to see this same siphon and growbed in use on an expanded system.

Join the Conversation


  1. Creuzer! Your YouTube vids and your blog helped me very very much!

    Now, I have been building a few prototypes of my own. Thanks for the great examples. Your depiction of the needed parts and how to assemble them made the thing much less intimidating. Your blog and Afnan’s blog are the two most informative I believe:

    I find that equilibrium is a problem, as you also noted and battled with. There are a few things about equilibrium I discovered with this application of the Bell Siphon:

    1) the small electric pumps commonly used for small aquaponics applications aren’t well regulated. The flow is easily and often reduced due to the pump’s heating up, age of the pump, or continuous operation of the pump affecting its efficiency.

    2) Getting small amounts of debris caught in the system, air in the system, and fungal or algal growth in the system or anything that restricts the flow even a little.

    3) Depending on both the size of the standpipe, size (volume) of the bell, volume of the outlet, and size (and type) of the air bleed/siphon cut-off.

    Equilibrium can happen at the beginning of the cycle or at the end of the cycle: A) Equilibrium happens while the sump is full and the Bell Siphon’s attempting to achieve full siphon, the partial siphon equalizes with the pump’s flow; B) Equilibrium happens at the end of the cycle when the sump is nearly empty and due to atmospheric pressure being reduced, flow is reduced to the point which it equalizes with the pump flow.

    In the first case, ‘A’ the stand pipe is too large or needs a venturi (like a small insert of plastic tubing in the stand pipe) to reduce flow (or increase velocity – as in the venturi) so that the outer “bell” will flood and allow the full siphon to begin, which will in turn drain the sump.

    In the second case, ‘B’ the stand pipe’s outlet volume is too small (or needs an extension to create more fluid momentum) which won’t allow the sump to drain to the point at which the surface tension of the water will be overcome by air pressure and the bell can be fully purged with air – cutting off the siphon’s flow.

    I noted that the flow capacity of the pump must be tuned to both the volume of the stand pipe, the volume of the bell and the air bleed cut-off. Too much flow and while it’s easy to establish the siphon (A) it’s more difficult to break the siphon (B). Too little flow, and although the siphon will break easily, due to the pre-siphoning effect the bell won’t flood to the point needed to establish full siphon velocity. The variability of the flow of the small capacity aquarium pumps is a huge problem. I suspect that some kind of flow regulator might really be the only way to get a system to work on a long term basis. Otherwise a system will work only with periodic adjustment and maintenance – constant tinkering. It’s going to work for a few days, a few weeks, a few months, then suddenly here you are left with equilibrium and no more ebb and flow.

    For a flow regulator to work, the pump must be of greater capacity than the bell siphon requires, probably at least 50% greater capacity. I’d guess it’d be safer with 100-200% more flow capacity than you require though. I’ve seen a few setups online with flow diverters or ball valves used to regulate outputs, but if the pump’s flow variates the way I’ve noticed that they do, a diverter will probably end up creating equilibrium problems too. I’m even wondering if the bell siphon is a good idea for a small, low maintenance system. It’s elegant and compact and simple in design, that’s obvious. It fits naturally into a sump or grow bed. It’s relatively easy to adjust. Undeniably it is really, really elegant. But – it’s really, really easy to end up with unexpected and undesired equilibrium states that leave your system with no ebb and flow.

    There are only two other (siphon) alternatives I’ve seen: A) The loop style autosiphon – which has really only one part, the looped hose; B) The “FLOUT” (a FLOating OUTlet Dosing System) which could be rigged with some hose and a small plastic flask with a hole cut in it. Both of these aren’t as elegant or compact as a bell siphon, but they are simpler to construct and adjust. I’ve seen many examples of the loop autosiphon, but almost noone’s using the flout. A flout is basically a bottle with an air hole in one end and a siphon hose in the other end. Here’s a diagram:

    I managed to make a small prototype from a vitamin pill bottle and some rubber tubing. I’ve gotten it to start and stop siphoning. I’m thinking of trying it on a larger scale, perhaps with a juice bottle. Also it needs much more room than a bell siphon or hose loop auto siphon – maybe even its own sump or at least a cleared section of sump in the grow bed. It’s definitely not as simple as just a hose loop. The thing I’m interested in experimenting with is how tolerant is it with varied pump flows? I’m surmising that it is virtually impossible for it to achieve equilibrium – once it’s set up right. That of course remains to be seen.

    Thanks again so very much for your blog and good luck with your mini aquaponics garden.

  2. To fix your problem with the bell siphon. Ether get a more powerful pump or add a u bend to the exit tube. That will add the extra pressure to start the siphon correctly.

  3. Hey dude,

    This is very cool! You’ve made a completely reverse approach to AP. Many people I know build the AP system from the ground up often with veges the central motivator. Very nice!

    On another note, are your fish looking happy nowadays?


    1. The fish I have in that tank now are all quite happy it appears, but they are fairly new to me.

      I’d since moved, and the AP system in in my basement (The local police took notice of that!). It doesn’t get the attention it had when it was in the living room, but It was really nice to have a fresh salad during last years big blizzard!

      1. Thats the problem, police have no right to take notice, I think this country is getting out of hand with this fear and police interference, Nice system though, you should look up Murray Hallam

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