Timed Flood and Drain

My pursuit of an energy efficient system continues.   Yesterday after about 6 months of flawless operation my bell siphon failed to drain.   This inspired me to find something simpler, less expensive and more dependable.  I remembered this conversation on AquacultureHub

By simply providing small drain holes at the bottom of the media bed a Hybrid Flood & Drain / Ebb & Flow can be created.   I have long been a proponent of Ebb & Flow due to the energy savings.

Here's how it works:
It's pretty simple.  There's a stand pipe that keeps the water from exceeding a set level about 1-1/2" below the gravel, and a weep hole (about 5/16") that drains the water out.  The pump comes on just a few times per day.  While the pump is filling the grow bed the water seeps out.  But the pump fills the tank much faster than the water leaves, so it fills.  The timer need only be set on long enough for the grow bed to fill.
In the Summer you may need to run the pump more often, but I run mine 3 times per day all year long.  The gravel stays moist and the water is aerated sufficiently for the fish.
By running the pump only a few times per day you save utility costs, and there is no siphon to fail.  I inserted a capped 1" pipe at the bottom of one of my grow beds and drilled my weep hole in it so that I could see it and this makes cleaning the hole very easy.  I can remove the cap to get inside if need be.  I've been running my timed flood and drain for several months and the hole has not clogged, but it does not hurt to inspect it once in a while. 
The timer I use is just a cheap $3.00 indoor timer with a plastic food storage container over it.  I poked a couple holes through the plastic, and plugged the timer in.  It stays nice and dry this way, and  easily accessed by removing the cover of the container.


Here are the conversations between John Burgess, aka RupertofOZ,   Glenn Martinez,  and J. Linden Rose.


System Design Considerations

Comment by J. Linden Rose on August 31, 2012 .

   Many people use gallon of fish tank to gallon of grow bed ratios. This has a minor flaw, because nutrient uptake and removal by plants is directly related solar surface area, and only indirectly related to grow bed volume assuming root development plays a large role in your particular crop. But before you can say something like 3 sq. ft. of grow bed per gallon of fish tank, you need to think about stocking density and feed conversion ratio (FCR).
   In this industry everyone is taught to sell their tilapia when they are no more than a year old. The reasoning is that when fish are small and young, the FCR is smaller, and less feed becomes more fish faster.  That's useful thinking in the aquaculture world, but lacks a certain breadth of consideration in the AP world. You might consider an aquaculture strategy that focuses on growing larger, older fish.  Remember that AP systems produce about $4 of produce for every $1 of fish in a Rakocy style system which has been optimized around fish production.  By lengthening the grow-out period for your fish, the FCR will increase, but it will also stabilize allowing you to have better control over the nutrient stream to the much more important produce side. Additionally, higher FCR means more nutrients end up in the plants than in the fish... which is where the money is. This in turn should imply that larger fish lead to larger grow beds.
   With that in mind, its probably a good idea to see your system as one that will go thru many changes when it is new. Then as your fish mature, and your nutrient stream stabilizes, you will be able to fine tune the grow bed surface area to match.
   Gravel beds, a type of fluidized bed reactor, are the oldest and most established form of modern aquaponics, and were first used in the work of Woods Hole researcher John Todd at his New Alchemy Institute, and Dr. Mark McMurtry at NC State.
   Dr. Jim Rakocy, a RAS (Recirculating Aquaculture Systems) aquaculture specialist at the University of the Virgin Islands in St. Croix, abandoned gravel beds because he wanted to work around the issue of sludge build-up. To avoid sludge issues, he developed raft culture, which in the absence of a bed reactor, required settling and degassing tanks. This system falls short of optimal for several reasons: 1) you're spending money on nutrients your plants need that you then remove from the system wasting resources 2) his floating rafts blocks most of the air-water interface for gas exchange intensifying the need to waste electrify on compensatory aeration, and 3) this system design is fish-centric, obsessed with how many fish you can cram into a barrel, when Jim's own publications showed that the aquaculture side was a minor contributor to revenues, and 4) only a very limited number of plants can tolerate having their roots immersed in water 24/7.  Typically plants with low nutrient requirements and low ability to scrub nutrients from the water.
   Tom Speraneo, is credited with the first use of tilapia in AP systems, but also is credited with cycling the water level in the gravel beds, creating enormous amounts of temporary thin water surfaces for gas exchange, and facilitating aerobic RAS waste processing. But the other interesting development was that it made the beds capable of sustaining active vermiculture, which further breaks down and decomposes the solid wastes, and restores lost nutrients instead of wastefully removing them.  This seems to have been confirmed by the systems popularized in Australia by Joel Malcolm and Murray Hullam, with Murray claiming to have systems that have run without any waste removal being necessary for over 3 years.  Similar results have occurred in Hawaii with Glenn Martinez's system.
   Using the archaic meaning of vermiculated of "worm eaten", we can call these vermiculated fluidized bed reactors, and their use should free up a great deal more nutrient from the same amount of feed input, allowing you to focus on the much more profitable produce production side of an AP system.
   With that in mind, Wilson Lennard has shown that raft cultures seem to be slightly more productive with low nutrient crops like lettuce, whereas most crops cannot be grown in rafts at all.  Since lettuce has a very fast seed to crop cycle, it can provide stead cash flow while waiting for more valuable crops to mature in the gravel beds, and with all the extra nutrients available, there's plenty of reason to have both in your system design.  This will also increase the total system volume, which is good for fish, and if you design your deep water wells with tops that are not floating on the water, you'll have greatly enhanced gas exchange surfaces.
   It would probably be a good idea to avoid NFT (Nutrient Film Technique) completely if your system includes fish production, because a thin layer of water spread out over long distances is basically a heat exchanger, which will cause diurnal temperature swings in your fish tank greatly adding to their stress levels.

Comment by Glenn Martinez on September 1, 2012

   First, most of us have fallen into a trap of running our aquaponic (AP) systems 24 hours a day. Think again....perhaps it should be shut down at night, drain the bio-filter (cinder beds) and let the system rest at night. Keep pumping the AIR to the fish, but stop running the water thru the vii-filter and float beds. This saves energy. It also allows the fish water to build up ammonia that will then be sent the bio-filter beds. Very quickly the bio-filter will convert the ammonia to nitrates.

   As long as you do not let the ammonia build up in the fish tank, you are okay. It is recommended drain the bio-filter bed when it is not circulating, as leaving water stilling in the bio-filter, seems to deplete the oxygen (everything is composting) and kills the worms and oxygen loving bacteria....

   The worms in our AP systems (cinder beds) eat the fish solids, breaking them down. Most important to keep in mind that our siphon system is NOT inside the bio-filter, but removed and located in an container that will drain the vii-filter "drip dry" at each flush. All of our bio-filter beds are "double tray" or false bottom, to allow drip dry draining. The drained bio-filter bed will NOT dry out over night and the plants do not suffer.

   To drain the bio-filter beds at night, place a small hole in the stand pipe of the bell siphon or install a small drain tube to drain the bio-filter bed when the water stops coming in for any reason , like a power failure.

For balanced nutrition, add vermicast or compost tea. That will supply all the micro and macro nutrients you need to grow NUTRITIOUS food, kala etc.

Food for thought.

Glenn, Olomana Gardens, Hawaii

Comment by John Burgess on October 17, 2012

   "To drain the bio-filter beds at night, place a small hole in the stand pipe of the bell siphon or install a small drain tube to drain the bio-filter bed when the water stops coming in for any reason , like a power failure."

Just run a standard overflow standpipe... and timer... flood & drain configuration... ditch the siphons altogether...

   Part of such a configuration... is the (generally) two small (6mm) holes at the base of the standpipe.. to allow the grow bed to "drain" during the timer off period...

   And utilising a timer based F&D... means it's simple as... to turn the beds off or limit/extend the F&D cycles.. during the night... or as a response to climatic variables...