Backyard Aquaponics
A place to discuss aquaponics

Hey Guys,
I'm new at the aquaponics thing, and have been studying, have made an attempt at creating a two barrel system using a bell siphon, and have encouraged a couple others to do the same. The same basic question seems to arise:

"What is the benefit of a siphon vice a continuous flow system?"

Can anyone answer this? Why use a siphon, whynot just allow continuous flow between the fish and the grow beds?

I would appreciate the elimination of this point of ignorance in my aquaponics education! ('Cause I know there are a lot more points I also need to deal with! )

Thanks,
Tony

For this - siphon and standpipe are placed together.

The siphon drains the water from the bed very quickly, drawing a lot of air into the media, and making the bacteria + plants happy.

A siphon system can have water pumped to it on and off, lowering the amount of time a pump is required to be on. However a siphon system will usually have a larger pump to compensate.

I use both types, and there is no real difference in plant growth, however the stocking densities are way higher for a siphon/standpipe system - a lot more gravel gets in contact with the water, a lot more often.

Continuous flow doesn't wet all the media, it allows deposits of solids to build up in the bed while the water just flows around it, and it requires extensive grid work over the beds to try and spread the water flow..

I vote for a flood and drain method where ever possible..

+1 - my cont flow system will be modified to allow more sump capacity, to allow the beds to become flood and drain. Soon

So to attempt to quantify (and geek out)...

Siphons are better than continuous flow because they allow the effluent from the fish tank to make better contact with more growing medium and for a longer period of time, and therefore more contact with conversion bacteria thereby cleaning the water more effectively than a continuous flow system and allowing for a greater fish density.

Further more, upon "flushing" air is pulled into the grow medium aeroating the growing medium and therefore the roots of the plants- which profit from this, and the energetic elimination of the water from the grow bins oxygenates the water more effectively allowing for a higher density of fish. Is this correct?

So if the above is a better way to do it and adds very little in the way of cost why do it any other way? What is the benefit of siphon over any other way? And I only say "continuous flow" out of ignorance. There may be many other methods in which I am unaware.

And it looks like others have managed to answer your question while my internet dropped out. I'll post this anyway even though it looks like you got the idea.

The reason for adding an auto-siphon into a system with a continuously running pump is to make the bed flood and drain (or ebb and flow if you like.)

I will attempt to address a few different ways this question could be taken since auto-siphons are commonly used in systems with the pump continuously running. I'm thinking your question is more about flood and drain vs trickle feed. I will share with you other ways to flood and drain if the siphons are giving you trouble.

If you hate siphons as some people do, you can make flood and drain happen using a timer to turn on and off the pump at the appropriate intervals and have a slower drain so that the bed will fill up while the pump is on and then slowly drain while the pump is off.

The benefits of flood and drain are numerous. When you flood most of the gravel in a bed, it gets evenly wet allowing more of the surface area to be colonized by the bio-filter bacteria and when the bed drains it allows air down into the bed to keep things aerobic. Flood and drain also works pretty well to disperse solids throughout the bed. It only requires a single inlet into the bed and therefore avoids much of the clogging issues associated with dispersion grids over the beds.
So the quick list of flood and drain media bed benefits:
1-good bio-filtration
2-good solids filtration
3-good aeration for bacteria
4-good aeration for plant roots
5-less clogging issues

If you are wondering why you can't have the water just trickle into the beds and flow directly out or keep the beds continually flooded and trickling through the overflow. Well you can but here are the issues you many have to contend with.
If you are just trickling the flow through the gravel leaving the bed essentially empty of water. You won't get the full benefit of the gravel surface area for bio-filtration or solids filtration. Most of the gravel will stay dry and only the areas getting water trickled over them will do any filtration. This method will work just fine for growing plants at least where the plant has access to the trickle (till it clogs up) but it won't give you much bio-filtration. The other issue with this method is to disperse the trickle of water through out the bed better you might make a grid with small holes. These small holes will get clogged with fish poo or food quite quickly and need lots of tending. Also where the water comes out of the grid, you will likely have solids building up on the gravel. This can work but be ware that the bio filter will be very minimal and therefore a very, very small amount of fish can be supported. (This method might be called trickle feed and be kinda akin to hydroponics drip feed systems or modified NFT with media.)

If you like the idea of a continually flooded bed, the main issue will be aeration. Yes all the gravel may be getting wet but it never gets air so the bio-filter may stall out on this one too and the plants are more likely to suffer root rot. Some people have managed to make this work at least sort of but unless you have lots of air stones installed under the gravel, you may have more trouble with the bio-filtration that you like.

Flood and drain just seems to me the easiest/cheapest/most elegant way to cope with all these issues all in one grow bed.

If the siphons are getting you down (which they can be a real pain in the tush in half barrels) you can effect flood and drain easy enough using a simple timer on the pump. Just make sure the bed has an overflow installed so the pump running longer than in takes to flood the bed won't cause it to overflow or hopefully not even wet the top of the gravel. Make the drain slow enough that the pump can fill the bed in say 15 minutes to a half hour but still fast enough that the bed will drain while the pump is off for say half an hour to an hour and a half. This can also save you a bit on electricity since the pump won't be running all the time. You probably will still want an air pump running for the fish though.

Hi Tony:

I think you should be calling it flood and drain, because there are two ways to get flood and drain - one with a timer and a standpipe, and the other with a (usually) continuous pump and auto-siphons (although OBO mentions you can use timers with siphons so that they aren't running all the time either).

The benefits of a continuous pump and siphon over a timer and standpipe are that the siphon will automatically flood and drain the bed tuned to the pump rate - the timers usually have very coarse increments (15 mins usually) and you can end up running the pump longer than necessary to flood the bed. I use sump pumps from Sears and have to bypass a ton of their flow and do not really need 15 minutes to flood my puny bed. The timer turning the pump on and off many many times can wear out the pump sooner. That said I use both, they are both valid ways of getting flood and drain but siphons might be a bit inappropriate in certain situations, for example if you do not have enough vertical fall to get the siphon going or if the bed is very large and it would be difficult to size a pump that could flow to the big bed fast enough to cause the water to rise fast enough to start a siphon reliably.

It might be more energy efficient to use a timer and turn the pump on and off than to have a pump sized to get a large bed's siphon going and running that pump continuously. For example the continuous pump I'm running is about 40 watts and the sump pump I'm running is over 100 watts. I have the timer set to not pump as often at night, it is set to pump more often during the warmest part of the day.

this has been covered many times before

viewtopic.php?f=1&t=97&hilit=+continuous+flow
viewtopic.php?f=1&t=135&hilit=+continuous+flow
viewtopic.php?f=1&t=3603&hilit=+continuous+flow
viewtopic.php?f=1&t=2861&hilit=+continuous+flow
viewtopic.php?f=1&t=2505&hilit=+continuous+flow
viewtopic.php?f=3&t=2251&hilit=+continuous+flow
viewtopic.php?f=1&t=2100&hilit=+continuous+flow
viewtopic.php?f=1&t=889&hilit=+continuous+flow
viewtopic.php?f=1&t=349&hilit=+continuous+flow

and that's just a few

I think all of TCL's informative posts should go into 1 page, and all new Ap'ers should be forced to read them before signing up. You have a way with the written word

I suppose it is just that when I learn something, I like to know the why of it so I assume that others would want to know why as well. It usually also saves the next couple standard questions that follow.

Sad part is, it is challenging to get people to read the top section of the forum before jumping in. I personally would rather answer questions up front though than try to help people who have already built in some particular way other than flood and drain who are then struggling to cycle with fish!

The benefits of flood and drain are clear, however they seem to be a bit tricky in terms of the size of sump and tank.

Ideally I'd like a system with one or two growbeds, because it's much simpler to manage and requires less plumbing. I find it difficult to work out what size sump to have and how to manage water levels so that my fish are too stressed.

I'm using coco husks and want to keep doing so because they are a sustainable material. They are also light weight, cheap and absorbent. Because they hold so much water I think that continuous flow with auto siphons may leave the roots a bit wet? A timer and stand pipe system could be better, however it seems I would need a really huge sump or risk stressing my fish with fluctuating water levels. Any ideas?

I would have said that a continuous pump Chift Pist system was the way to go...

But as you're using the coco-husks, which retain water so well.... then I don't think you've any real option but to go with a timer based scenario...

Might all depend on just how quickly you beds (husks) dry out in your temps... but you can always either adjust the timer.... and/or incorporate siphons for quick "drain" and flood more often if required...

I've already set up the auto syphons, so changing to the timer system is tricky.
The coco husks are in large chunks, so there's still a lot of gaps for air. Do you think it's too wet? The plants look fine so far, but it's early days.

When I tried coco-coir.. yes... but I don't have the temperatures that you have, which will dry the beds so much quicker....

Incorporating a timer into your existing auto-siphon system isn't a problem.... the auto-siphons will only kick in when they need to....

i.e rather than maybe siphoning 3-4 times/hour when you run continuously... you might only fill the beds and initiate the siphons 1-2 times per hour... depending on timer settings...

The thing to watch for will be whether or not you're getting enough oxygenation back into your tank....

You could keep your oxygenation up to the tank... and limit the number of times your growbeds flood and then siphon drain....

By cutting in a return just above the pump.... diverting most of the flow back to the fish tank...

Keeps the oxygen up.... takeing longer to flood and drain the beds.... and run the pump continuously ...

But then you're back to how "wet" they stay for how long.... and whether or not (given temp) this is too long...

As you're basically setup this way anyway... why not just run the system as is... but reduce the flow to the growbeds by cutting in a return line...

You can always replumb it (or incorporate a ball valve) and change to a timer later...