Aquaponics - Ultra slow flow siphon problem

For some time now I've been working on an approach to invention and problem solving that, in my house, has become dramatically known as "The Invention Engine". It's a formalized structure to problem solving, and so far it's been working very well. It's all in my head at the moment, but at some stage I'll put it out to the world in some form. I'm testing the process again by finding a solution to triggering a siphon with an ultra slow flow.

In some recent trials, it looks like there may be some advantages to a constant flood grow beds, rather than flood and drain. This relies on having highly oxygenated water, but you should have that anyway because that's what your fish like. Some plants prefer flood and drain, but a lot seem to enjoy constant flood.

I can't help but think that one potential downside to constant flood, is that there may be areas that could  become stagnant. Flood and drain, on the other hand, pulls all the water out on each cycle, so there are no areas that miss out on turnover with new water. My fear is that it might be possible that constant flood could leave some areas to could go rotten over time.

I thought I might make a grow bed that was constant flood for most of an hour, drained once quickly, then have it repeat that pattern for ever.

Tricky.

Constant flood works by having a standpipe sticking up through the bottom of your grow bed at the height you desire the water to sit. You pump water in constantly, and it overflows into the fish tank via the standpipe.

So my solution would be to put a bell over the standpipe, but with an oversized standpipe that would be too big for the flow, so that it didn't trigger.

Now all we need to do is introduce a new, quick flow of water once every hour to trigger the siphon.

The Invention Engine first casually mentioned I should just put a second pump on a timer, and have it supply the hourly additional dump of water. I told it that a solution like that was too easy and expensive, and really needed a rethink.

I added the following parameters...

1. that it should require no additional pump
2. that it should require no electronics or timers

The Invention Engine suggested I divert a flow of water to a bucket sitting over the grow bed, put a second bell siphon in it, and have the water dump quickly to trigger the main siphon.

"OK" I  said. But how do you make a siphon that takes an hour to trigger, but still delivers a rush of water to the grow bed. A siphon with a very slow inflow can only trigger if it had a very small standpipe. Any flow that took an hour to fill a bucket, would only trigger a tiny siphon, and only deliver a tiny amount of additional water to the grow bed. A tiny additional flow would mean some very accurate calibrations to make the grow bed's main siphon trigger. In fact it might not be possible, and would definitely not be reliable.

"Make it huge" The Invention Engine replied.

"I want it small" I insisted.

"Oh" said The Invention Engine, "A small bucket that takes an hour to fill, but then dumps quickly?  That's a different question altogether".

Aquaponics - Slow leak drainage system

Rather than running a siphon, because my pump is much bigger than it needs to be, I'm going to try a slow leak system.

I'll set it up so a bell siphon will work in it if I ever add another grow bed, and my pump needs to be on all the time. But right now my pump only needs to run for around 10 minutes per hour to turn over the water, and fill the grow bed.

click to play animation if it's not already playing

A slow leak system has a standpipe with a hole in the bottom. It also has a high inflow that fills the growbed faster than the small hole in the bottom of the standpipe can drain it. This means that the growbed would overflow if not for the standpipe. The standpipe allows excess water to overflow back into the sump tank, or fish tank. The height of the standpipe sets the maximum depth of the water.

The timer is simply any digital timer with a power point. You plug in your pump, plug the timer into household power outlet, and set when, and how often you want the timer to trigger the pump.

The aims are twofold.

1. To turn over 100% of your fish tank's water every hour (for the sake of your fish)
2. to fill the growbed to its maximum height at least once per hour, and have it drain back out again before re-filling (for the sake of your plants, and the nitrifying bacteria)

In my case, I estimate I'll be running the pump for around ten or fifteen minutes per hour, but that might require some adjustment after taking some water tests. It's difficult to estimate how much water my pump will actually shift in ten minutes, because I'm not exactly sure how high it will end up having to pump. The higher it's pumping, the less water per minute it will pump.

If this turns out to not work as well as I thought it might, I can always revert to a bell siphon, by simply replacing the standpipe with one that doesn't have a hole in it, and adding a bell.

Aquaponics - Calibrating a new bell siphon

This post assumes you know something about bell siphons, and roughly how they work. It also assumes you have made one and want to get it to work. If you need a bit of an introduction to this device, it might be worth reading this post first - aquaponics - bell siphon

With anything that you are trying to calibrate, whatever it is, the most important thing to do is make sure you are changing only one thing at a time. 

It's possible to make a bell siphon work with all kinds of different approaches, but in its simplest form the standpipe drops straight down from the grow bed, and the water flow isn't interfered with in any way

By having your standpipe drop straight down into air the only thing you can change is the flow into your siphon. The easiest way to do that is to put a tap on the inflow to your grow bed, or a tap that diverts some water away from the pipe going to your grow bed, and dumps it straight back into your fish tank. Plastic taps cost about $2. Don't use a brass or galvanised iron one or anything metal because it might poison your fish.

Turn the single outlet from your pump into two by adding a T-junction between the pump and the grow bed.

Make one of your two new outlets go up a bit higher than the other. This one is your excess overflow, and needs to be diverted back to your fish tank. The reason we make it go up a bit higher than the other is so that it becomes the lest preferred way for the water to travel. Water hates traveling uphill, so it will prefer to go into the lower pipe with the tap attached. Only when the tap is turned off a bit will water flow through the higher pipe, and overflow back into the fish tank.

The other outlet gets the tap, and continues on to the grow bed.

before you start...

- make sure your breather pipe is 2cm away from the bottom of your grow bed.

- make sure the breather pipe is breathing fresh air when the water is low enough. Its possible, if the breather is a narrow enough pipe, and is hard against the siphon, to form a meniscus so that it sucks water even when it is above the level of the water. Check that the breather pipe is sucking air when it should be sucking air.

- make sure the water can flow through your media screen fast enough. If you have a screen made with holes drilled in it and there are not enough holes at the bottom, the flow through the media screen can reduce as the tide goes out. This can make for false stops. When the siphon stops, the sudden small amount of water that flows back out of the bell can create a localized increase in water depth. This can reseal the breather, and also kick off the siphon again if it hadn't completely stopped.

Steps in tuning your bell siphon might be (for a tap that is at the end of the pipe to the grow bed)...

1. turn on the tap to a midway position.

2. wait until the water gets to the top of the bell where it should trigger.

3. if it doesn't trigger turn up the tap and go back to step 2. If it does trigger wait until it empties.

4. if the siphon doesn't stop when the grow bed is empty turn the tap down a bit until it does.

5. wait until it fills and see if it triggers properly at the top. If it does, watch it cycle way too many times, drink beer and bang on about it to your friends (I recommend a glass bell siphon to this end). If it doesn't, adjust the tap so the flow is reduced a tiny bit and repeat.

The object here is to adjust the flow in ever smaller amounts until you narrow in on the correct flow. Once achieved, the flow should start within a few seconds of the first flow of water from the standpipe, and should stop quite suddenly. It will probably take 4 or 5 cycles to adjust.

If you still cant get it to operate, there is a fair chance your pump and siphon don't match. Try adding an inner sleeve to the standpipe to reduce its diameter.

Trouble shooting siphons

Any air in a bell siphon should just exit down the standpipe as the water rises and the pressure inside the bell increases. If it doesn't, then there is a fair chance the exit pipe isn't draining freely. With air in the bell, it's possible that your bell might float, and not trigger.

Some people say its a good thing to have some water in the exit pipe, but after a stack of experiments, I found that even though having some water in the pipe often fixes a problem siphon, a bell siphon will be much more reliable if you have a clear, straight down exit that is flowing into just ambient air pressure. That is, dump from your standpipe into fresh air, then catch the water in a drain to take back to your sump, or just drop it straight down into your fish tank if that's your arrangement. At the very least, make sure your drain is running downhill all the way to the end. It makes it a lot easier to get the flow right if your are only dealing with one variable.

The more simple your system is, the more reliable it will be.

Getting your flow right is a much better solution than adjusting your drain by putting bends in it, adding uphill sections, or submerging the end. All of these things can get a siphon to work that otherwise might not, but dumping to ambient air pressure, and adjusting the flow until it works, will make for a very reliable siphon because this makes for only one variable, and with a tap, you have total control over that one variable.

Keep your system simple, and it will reward you with reliability.

Aquaponics - Puddle flange

Who would have thought there was a need to call something a "puddle flange"? It turns out there is such a need. In fact, I just bought one.

A flange is normally a thing that flares out from the size of a pipe, to something at right angles to that pipe.  It allows you to connect it to another flange with bolts.

Puddle flange

A puddle flange is a PVC something, that flares out from the size of a pipe, and connects to a puddle.

It turns out, the thing you have in your shower around the drain is a puddle flange.

I found one that has a hole in it that perfectly fits a 50mm PVC pipe.





I'll stick a 50mm pipe into the hole to act as a standpipe, and silicone the puddle flange into the hole that's in the bottom of my new grow bed.

Because I bought a pump with expansion of my system in mind, it's too powerful to need to run it 24/7. I'll be putting my pump on a timer, and running it for perhaps 10 minutes per hour. This means I will probably settle on using a slow leak approach rather than bell siphon approach to drain my grow bed.

The slow leak approach will involve putting a hole in the bottom of the standpipe, just up from the bottom, so that in time all the water will drain out. The standpipe is there as an emergency overflow pipe.

If for some reason the water fails to drain out of the grow bed, on the next cycle, the grow bed might overflow. With a standpipe as an emergency overflow, the grow bed might remain flooded, but the water will overflow back into the sump.

I'll drill a small hole in the standpipe to start and see how long it takes to empty the grow bed. If I need to, I can then drill larger and larger holes, until the grow bed drains over the space of about an hour.

I'll also be setting the drain up so that if at some stage I need to change the system to a bell siphon based one, all I'll have to do is replace the standpipe, and add a bell.

Aquaponics - Bell siphon

The bell siphon was a clever thing for someone to design, and as such you feel a bit of that "clever" rub off onto you when you make one. I made one, and feel a slight increase in my cleverness.

There isn't that much to a bell siphon, but what little there is tends to be very important.

A bell siphon consists of ...

- a standpipe (the bit that goes through the bottom of your grow bed)
- a bell (the bit that sits over the standpipe)

A bell siphon can also have...

- a siphon breaking air tube
- water inlet holes
- a media screen (cut off soft drink bottle with holes)


The bell sits over the standpipe.
The siphon breaking air tube is a tube that goes from the uppermost chamber formed by the bell, to a point around 1.5 cm above the bottom of the grow bed. If you dont have the tube, its possible for the siphon to continue draining the grow bed as the water is being pumped in. That is, when the siphon should have stopped and the bed should be filling again, it is possible that water will just keep flowing out at the same speed that its flowing in. By allowing a small stream of air into the top chamber you can break the siphons ability to continue suction when the water gets low enough to expose the pipe. When the bed is full and the siphon starts, this tube doesn't really do anything because its sucking water not air.  But as soon as the bottom of this tube is exposed to air, it brings the siphon action to an abrupt halt allowing the cycle to start again.

A bell siphon also has some cutouts to allow the water to flow in unrestricted. These can be cut outs or a series of holes drilled near the base.I used cutouts.

Make the standpipe not too tall (so water doesnt get blocked by the bell sitting right on top of it) and also wide enough to allow enough water to drain through it. The standpipe needs to have a diameter large enough to allow the water to drain faster than the pump is pumping water in. A large diameter standpipe is important, but dont go too large. If the standpipe is too wide the water will be able to run down on only one side and never form the seal required to start the siphon. If this happens the water will just flow out at the same rate the pump is pumping it in. To get the siphon to start, reduce the size of the standpipe or increase the flow rate of the pump until it's flow fills the tube.

Some things that will cause your bell siphon to fail are...

- air bubbles in the hose running back to your fish tank. (keep it free of kinks and always sloping down - the return hose should drain until it is completely empty at the end of each cycle)
- too small a diameter of standpipe for the flow (or too much pump flow)
- too large a diameter of standpipe(or not enough pump flow)
- gravel getting into your siphon (make a media screen)
- water entering your standpipe too much from one side (cut your standpipe so that its level to help get a rush of water all at once when the water level gets high enough - this helps fill the tube and start the siphon)
- having too small a gap at the top between your standpipe and the bell (make your bell taller)
- restricting the flow within the bell because there is not enough gap for water to travel up the bell (make your bell wider)

Even though aquaponics is a fascinating subject, when you make a bell auto-siphon those around you will tire of your company quickly. Try to include other topics of conversation when meeting friends. Other people wont find your auto-siphon as interesting to watch as you will.

[link from the future on calibrating a new bell siphon]