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If you are growing using Flood and Drain on a timer, how often to you cycle and for how long?  I think most of us use 15 minute interval timers, so I'm guessing that the duration of a cycle is typically 15 minutes - I know mine is.  I tend to go 30 minutes between cycles if everything is nicely balanced and only 15 minutes between if I'm overstocked with fish and need the oxygen more than the plants need the dry period - which is where I am in 2 out of 3 of my systems now.  The other data point I have is Joel at Backyard says he typically goes 15 on / 45 off with his systems. 

What do you do?  What have you found works best, and what just doesn't work?

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Kobus... I wasn't defending any particular method, and as indicated I, along with others were geniunely surprised by the performance in relation to both timed, and siphoned beds...


I'm not pushing either, or any of them... and as Murray says, and even I suggested in a post on BYAP... more time is needed, and it could well be that over time the results may change... as they appear to be...


I just don't think it's necessary to suggest a "horse" is being ridden, or that the experiment was set up to favour a particular outcome...or that I'm biased toward people that "shine up" my preferred method... I can assure you that was not, and isn't, the case...


Granted because Joel has a "vested" interest, there is some validity to the question being asked...


And nothing intended to be a criticism of Murray, yourself or anyone else that utilises one method over and above another...


Anyway, lets move on.... as you say, different people have arrived at different methods by their own choices...


Murray's point about media is an important point that needs to be part of the equation, and I think a similar point has been suggested for any further trials...

By the way... I prefer to use the term "constant flood" to describe the bed concerned in the trial...


Rather than continuous flow, which I associate with raft or raceway style DWC....

Kobus, I think when Rupe said he was surprised that the continuous flood was working so well, I believe he was actually referring to the trial at the BYAP shop.  I only say this because we both expressed that over in the BYAP Trials thread at one point or another.


What I would have expected from the systems would have been for the Timed flood and drain plants to do best with the Siphon flood and drain to be in the middle and the Constant Flood/Flow to come in last and it was really interesting that was not the case.  It is handy to note that the Constant Flood/Flow system Bio-filter was cycled up faster while the siphon system was in the middle and the timed flood and drain was lagging behind.  Start up by constant flood might be appropriate and then switch to siphon or timed flood and drain.


As to what the Constant Flood/Flow is.  I think that is different than what Murray was doing as Constant flow.  My Constant Flood beds are flooded, not just an inch or two in the bottom.  They Have a stand pipe like you might use for timed flood and drain but without the holes in he bottom.


Now I've been known to temporarily flip my stand pipes over and add more water into a system and gut the indexing valves to run constant flood to help maintain a steadier temperature during extreme conditions.  Biggest challenge there is to keep the flow out all the ports balanced but it is usually only for a week at a time.

And for anyone who repeats this experiment - and I hope many people do - I suggest triple redundancy so there are at least 3 systems running under each scenario.  that way if the pump fails on one the whole experiment isn't ruined.  Also allows you to average the results of the test beds that successfully reach the end trial to wash out possible unintended biases.  Those might be one pump being older and less powerful than another, more solids buildup in one bed over another, sun hitting the beds at different angles, a fish dying (or having offspring) partway through the trial, a disease or infestation of some kind that isn't detected.  When I used to run grow trials like this we never used fewer than 3 systems per set of test criteria.  Having the test structure, data capture methods, and results reviewed by an independent third party couldn't hurt either.  Anyone have 9 grow beds available? 

RupertofOZ said:


Murray's point about media is an important point that needs to be part of the equation, and I think a similar point has been suggested for any further trials...

I personally think that there are so many variables in this scenario that it is almost not worth trying to do this really.  To have all the systems running under statistically comparable conditions (9 if we take Sylvia up on her request) will be next to impossible.  Runt fish, runt plants, exposure to sunlight, exact amount of feed input, identical fish and plant starting densities, identical component materials........I think the first challenge would be just to build two IDENTICAL systems that behaved the same!  I have seen aquarium set ups come and go and try as you please, I have not been able to set two identical ones up ever.  Like these things will always have their own DNA or something.


Honestly, if a plant can grow in a raft (100% of the time in the water) I do not really think that we have serious issues to debate around whether this or that method of flood and drain is going to save the earth's food supply one day.  I think the differences comes in at system management level, looking at the critical biochemical factors that make the aquaponic process work.  A few days here or there where the temperature was off or the pH misbehaved or if the sun did not make it out of the clouds for a week can have even more telling effects than timed cycles, IN THEORY.  There, in nature, wetlands beat all other systems for productivity hands down and they are flooded all the time.

It has been suggested that to more accurately judge if a particular grow bed configuration is better for the plants or not, that all the grow beds need to draw from the same water source.  However that won't tell if a particular bed configuration is better as a bio-filter.  So there are dozens of trials that "could" be done when some one has the money, space, materials and time to set it up.


Murray's point about the media in his trials I'm sure is significantly linked to the fact that his Constant Flow beds were NOT Constant FLOOD/Flow.  Two very different situations.


However, any trial done, make sure that only one variable is changed at a time.  If trying to test different flood methods, one should make sure to use the same media.  If testing different media, one needs to use the same method for the trial and then this might require a separate experiment to test the different media in a different method.


I'd love to be running all these experiments for you all, I don't have the means to afford it at the moment through.

You and me both TCL... although in the very near future I should have two identical 3 bed systems within the same greenhouse...


I'll see if the client will let me experiment... need to sign the contract first though...

Much thanks for the input.  I guess I was overdoing it and thought that you were supposed to time your pump for 15 on then the bell siphon kicks in after it reaches a certain height inside the bed, but I don't think I had it right. We've put together a bell siphon, but it seems the water inflow must be fairly fast to kick the siphon on, and then it drains very rapidly therefore, the water has very little time in the media bed itself.  If you use a timer (15/45) do the beds had small drain holes that trickle empty the beds after a certain amount of time?   How long should the water ideally sit in the media beds for good absorption and conversion to nitrates??  What's your favorite/easiest way to drain your beds? 

Sylvia Bernstein said:
Hey Allisyn.  I'll jump in here and try to answer a few of your questions.  Frank lives in Australia and grows using Murray Hallam's systems from Practical Aquaponics so I'm pretty sure he is using an auto-siphon.  With media based systems you are absolutely right - you want to flood then drain your beds to draw oxygen into the planting beds (although I hear rumors that some people are having luck with continuous flow I wouldn't recommend it for someone just starting out).  This is generally done in one of two ways - with a timer on a 15 minute on and 45 minute off cycle, or with an auto-siphon (a bell siphon is the most popular design of an auto-siphon for APers).  If you use an auto-siphon you don't need a timer...and I think that is what Frank was talking about.  His pump runs continuously because the auto-siphon takes care of draining the beds.  Our company (The Aquaponic Source). is planning on launching a new Bell Siphon product in the next month or so (my husband is putting on the finishing touches now).  Alternatively you can check out Affnan's blog for great bell siphon videos and instruction (he is also a member here so you could send him a message) or Murray Hallam's Bathtub Aquaponics guide also has very good, step by step instructions for building a bell siphon (he is also a member here).  Hope this helps!

I don't like water to just "sit" in a bed ever. 

I like there to be constant flow of water through a constant flood system.

In a siphon system, I rather prefer to let the pump run continuously so the bed is re-filling as soon as the siphon kicks off and you are never left with the bed either sitting empty or full.  I don't really personally believe there is much use for siphons and timers together in the same system under most normal circumstances.

And Timed flood and drain, well I like the timing and the holes to be set up so that the bed fills or even spends a bit of time overflowing down the stand pipe before the pump turns off and then the off time should allow the bed to reach the basically drained point before the pump gets back around to that bed.  Now it should be noted that the beds drain faster at first and as the water level in the beds decreases the flow out of the bed slows to a trickle until the bed might continue trickling for hours before no more water drips out.  Anyway, The bed should have reached the "trickle" stage by the time the pump gets back to it usually.  Of course if the weather is extremely hot you might want to flood more often and disregard the drain to a trickle rule.  Most of my flood and drain beds are actually double depth though so I have water still getting lots of media contact time even while my plants are getting extra air time so to speak.


Not sure if that really answered the question.  During initial cycle up extra water/media contact time will speed cycling.  Later on one might adjust flood cycles in a timed system to balance good bio-filtration with desired plant production.

I must admit that I'm confused. One of my beds has irrigation grid pipes which i call constant drip or drip irrigation..........and this is not the same as constant flood? I do have 2-3 inches of water off the bottom in the bed. To me it's better than the F&D next to it, i think this is because of the pea gravel but that's a whole other topic.

Well when you trickle water through a bed that is like 12 inches deep but there is only an inch or two of water in the bottom of the bed, it isn't flooded and I might call in continuous flow or trickle through but NOT Continuous flood/flow.  While a continuous flood/flow bed in my book is one that is flooded to a similar depth as a flood and drain bed might be at full flood.  So in my continuous flood/flow beds the water is only an inch or so below the gravel surface (or over the gravel surface for my water plant beds.)


So while a bed might be continuous flow with only a small amount of water in the bottom of the bed (which makes it more like a modified NFT) that is different than a continuously flooded bed.

So perhaps the constant flood/flow beds should be called CFF to differentiate from other constant flow techniques. 

There seems to be so much confusion on terminology it might be best if we make an  "aquaponics definitions" page to go along with "what is aquaponics" and "rules of thumb" on the home page.

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