Basic Media Bed Aquaponic Design

In some places I’m known for my patience in re-explaining many of the basic info needed for stable home aquaponics system design.

Things like the three major functions of media filled flood and drain grow beds (actually there are more than three functions.)
1-Media filled flood and drain grow beds provide Bio-filtration
2-Media filled flood and drain grow beds provide solids filtration
3-Media filled flood and drain grow beds provide plant support and space for growing
Now we get into the additional functions that many people might forget about.
A-Flood and drain media filled grow beds do all of the above functions without needing any additional aeration.
B-Flood and drain media filled grow beds provide a great home for composting worms.
C-Flood and drain media filled grow beds provide for mineralization of solids.
D-Flood and drain media filled grow beds don’t require net pots or separate seed starting facilities.
E-Leaves don’t foul up outdoor flood and drain media beds
F-Algae isn’t a problem in flood and drain media beds
G-Flood and drain media filled grow beds give you a place to set down your drink as you use extravagant hand gestures to explain some point during an Aquaponic gathering or system tour.

Perhaps there are other points in favor of flood and drain media filled grow beds but there are a few points on the negative side.
-Flood and drain media beds can have a huge impact on temperatures, they make very good chillers on cold nights and they are great water heaters on hot summer afternoons. (constant flood during these times might be appropriate.)
-Gravel is heavy and a pain in the back to wash/haul.
-Lighter manufactured materials are costly and still need rinsing.
-Flood and drain causes water level fluctuation or requires a sump tank or sequencing valves.
-timed pumping can be hard on pumps
-variation in sounds from pumps turning on/off or siphons kicking in/out draw attention to the noise (constant sound fades to the background most of the time.)

Still, I like the gravel beds for their ease of use once installed. If a system is properly designed (has enough grow bed to handle the fish load) the gravel beds provide for a very low maintenance system able to be left to fend for it’s own for a few days. This is important as I travel often and need something easy for the neighbor to check on. If you are going to do NFT or Raft(DWC) systems, you will need separate ways to deal with solids filtration and bio-filtration. With media beds, they take care of solids, bio, and plant space all in one.

Next primary bit of information people often need for designing their home aquaponics system. How much filtration is needed for some given amount of fish. Here is the rule of thumb I learned.
3 kg of fish in 50 liters of water with 100 liters of grow bed or 6 kg of fish per 100 liters of fish tank with 200 liters of grow bed. THAT IS THE MAX!!!!! Ok so for my poor brain I rounded that out to an easy imperial measure to remember. 1 lb of fish per 5 gallons of gravel (again that is MAX!) Now keeping in mind that you can’t really flood 100 liters of grow bed from a 50 liter fish tank and expect your 3 kg of fish to still be happy. To run this 2:1 ratio, you must have some method of dealing with water level fluctuations. That method traditionally was a sump tank, now there are more options with things like indexing valves.

Instead of using the above numbers, I now usually recommend something more like 20-25 fish per 500 liters of grow bed (assuming fish only being grown out to 500 grams) or 1 fish per cubic foot of grow bed media assuming 1 lb grow out of fish (1 cubic foot is around 7.5 gallons.)

Now I would never recommend some one try to grow a 1 lb fish in only 2.5 or even 5 gallons of fish tank. I’ve read a few places that say you can grow an eating size fish in something as small as 50 gallons, well perhaps you can with a fish as forgiving as tilapia but I like larger tanks. Very small fingerlings are fine in small tanks and I currently have over 100 small catfish in a 100 gallon tank but for grow out of large fish like catfish, my personal minimum size tank would be 300 gallons. I like a 600 gallon tank to grow out really big catfish. 300 gallons is also a good size to have more temperature stability.

Pumping, now this is more important that many people think. How big a pump do I need for my system? Well the simple rule here is you should aim to pump the volume of your fish tank each hour. So if you have a 300 gallon fish tank and your design will have the pump run constantly, then you need your pump to move 300 gallons per hour at whatever height you will be asking of it. (A pump with a nominal rating of 300 will probably not move 300 gallons per hour once you hook it to plumbing and expect it to lift that water two feet above the surface of the fish tank.) Most good pumps should have published curves or information that will tell you aprox how much water it will move at different head heights. Now if you are going to be doing timed pumping, you need your pump to move at least the volume of your fish tank during whatever portion of an hour you will have your pump on. So if you plan to run 15 minutes each hour, then you should get a pump that will move 4 times the volume of your fish tank at the needed head height each hour. Then when you run it for 15 minutes, you will get the circulation you need. It is always wise to allow extra flow a bit beyond what you think you will need.

Plumbing and pipe sizes. Oooooh this is a stinger
So many people start their first systems with too small of pipe and find out later they should have used larger. Yea, the bigger pipe and fittings costs more but buying both the smaller stuff and a set of the larger stuff costs even more yet. Please remember that in Aquaponics there is this stuff we call bio-slime that can clog small piping. Algae can clog piping as well. For larger pumps, I’ll connect the pump according to the pipe fittings the pump comes with. For small pumps, I now adapt up to larger pipe and I’ve found that a little tiny pump can sometimes actually move much more water than I expected. Even my ten gallon aquarium with a 20 watt pump is adapted up to 1″ and 3/4″ pipe.

Gravity drain plumbing, MAKE IT BIG!!!
Example, My big system, the pump uses 1 1/2″ pipe, about half of the flow from the pump is being sent to the fish tank (probably 30 gallons a minute) the SLO (solids lifting overflow) drain from the fish tank is 3″ sewer pipe. If I were to send all 60 gallons per minute from my pump to the fish tank, it would overflow even with the 3″ drain. I know it is a real bummer cause the really large fittings get costly but so would overflowing the system and burning up the pump when the sump runs dry. Some people will use two 2″ fittings instead which can work but keep in mind that the more pipe walls you are dealing with the more resistance. In other words, two 2″ pipes does not equal one 4″ pipe. A pump pushing water through a 1/2″ pipe can still over top a 1″ overflow. And then remember that the overflow will probably have grills or mesh over it and that can clog too (on to a next important point.)

Fish will swim through pipe.
I’ve had a 2 inch fish swim through 3/4″ piping with six elbows! I’ve had tilapia fry make it through a gravel bed to get into the sump tank where they rode through the pump to get into a different fish tank!!!! And one of them survived!! But you can’t expect them all to survive or even expect any of them to survive. Most fish find that sunning them selves on the surface of a grow bed to be very bad for their health. However, finding the fish on the grow bed is a little more pleasant than discovering one in a ball valve, or more accurately part of one in the ball valve “I wondered why that was so hard to close!” I’ve found that most fish find NOT swimming after eating to be very dangerous. I guess this will bring us to the next topic, tank covers. Most of the fish I find out of the tank get eaten by something else, like my chickens.

Fish tanks should have covers.
1-Fish tank covers keep fish in. Any fish tank that doesn’t have a huge amount of extra depth above the water line risks fish jumping out.
2-Fish tank covers keep debris out. In outdoor systems things like leaves can really clog up the works. Even with a tank cover some leaves are gonna get in but a cover will keep huge amounts of plant matter out of your fish tank and also the screens, grates, pumps, traps and plumbing.
3-Light. Shade the tank to keep excess sunlight out and avoid a major algae bloom. Pea soup can really mess with dissolved oxygen levels even to the point of killing fish. String algae can just gunk things up and create more work in pump/screen cleaning. A cover over the tank will keep light out or at least make it easy to throw extra fabric, shade cloth or a tarp over to block the light and stop the algae.
4-children and pets. Kids love to play in water but if you have children around, make sure your tank cover will keep them out unless supervised. I also recommend covers if you have ducks around or dogs/cats that might manage to get into trouble while trying to sneak a snack.
6-Since my property isn’t fenced, I’ve also added a lock to the cover on my large tank. Yea I know it will only keep honest people honest.

Next topic,
Galvanized tanks, Don’t do it!!!!!!
Metals!!!!!!!!!! They are generally not appropriate for aquaponics.
Many metals can quickly corrode in aquaponics. They can build up to toxic levels for fish in a recirculating system. Of particular importance to note are copper and zinc. Both can be particularly detrimental to some types of marine life. Galvanized tanks can leach zinc into water and it becomes more problematic the lower the pH. Copper plumbing can leach too. In our household plumbing this in not normally a problem as the water is only taking the single trip through the plumbing but in an aquaponics system the water circulates through the parts constantly and aquaponics also sometimes tends to the acidic side which can speed the process. Hence a copper coil would not be a good idea for a water heater for aquaponics. There are other metals that can be an issue (perhaps nickle from chipped bathtubs) but copper and zinc are the two that cause the most issues in Aquaponics in my reading.

Look for something that won’t affect your pH. This rules out limestone and marble since they will cause a really high pH. Also, I don’t recommend shells, my system is full of them and my pH stays at 7.6 unless I’m really overloading it. I’ve heard that Diatomite will lower pH but one might want to be careful if growing trout in such a system since it apparently also has levels of zinc that might be bad for trout at the lower pH. I like river rock of 1/2″ size. Lava rock can also be good if you can get it in the right size range but it is really difficult to get washed very clean. Some people have lately been experimenting with expanded shale but getting it in the right size is a challenge so sifting it for size may be necessary. Clay balls are great if you can afford them and your back can’t afford the lifting of gravel. I recommend using small buckets and baskets for the washing. I can do the washing so long as I don’t lift too much at any one time. Set up the washing station so you don’t have to bend over too much and it can be done without injury.

Plumbing a bypass
Don’t restrict your pump. If your pump gives more flow than you can handle, then use a bypass. Simply a T back into the same tank where the pump is located. Put the ball valve on that flow and adjust the ball valve till the flows are balanced as needed.

I hope these things help more people on their journey into Aquaponics System Design.

(Originally posted by TCLynx on Aquaponic Gardening Community on May 27, 2010)

21 comments to Basic Media Bed Aquaponic Design

  • Mohammad Panabad

    Dear Sir/Mm

    I am looking To set up an Aquaponic Farm and I need more guide line for this matter thanks a lot for your cooperation.

    best regards

  • TCLynx

    Mohammad Panabad,
    I just sent you an e-mail.

    I have added a page to the site that may provide some assistance to those seeking aquaponics help. There is a form at the bottom that will send an e-mail to me.

    Aquaponics is often very site/situation specific so knowing more about the specific situation/goals will help much in making informed recommendations.

  • […] recommend learning a bit about basic system design and reading about cycling up a system (Fishless cycling) and using the test kits before you go […]

  • mike heery

    they more i read all about aquaphonics the more complex it seems to become, i send so many videos links to kenya and nigera and uganda and i end up more confised my self and i know if i get started it seems ti will cost me a small forutne. i live in ireland the the weather is so cold and stil i do not even know what type of fish i should use. then i read all about the problems i get put off,.,.someone give me cheerful uncomplicated info plzzzzzz and iam an engineer,,..

    • TCLynx

      Aquaponics is really very simple in concept, however there can be a heck of a lot of details to hang you up and you know what they say, the devil is in the details.

      Don’t depend on a YouTube Video to teach you all you need to know about aquaponics since many YouTube videos only show you how to hook things up and they don’t necessarily come back years later to show you how things have done over time or if the system even survived through bacteria cycle up.

      Simple, put fish in a tank, pump water through a pH inert gravel bed and let it drain back to the tank, don’t use too many fish, choose fish that are appropriate to your climate, grow seasonally appropriate veggies, feed fish (but not too much) and test the water quality regularly, keep topped up with water.

      There are good books out there you can buy, or you can download the Barrel Ponics Manual or the IBC of aquaponics for free. The Backyard Aquaponics Forum is a great resource.

      Maybe one day I’ll write a book but I don’t have the time/money to do it for you at the moment.

  • r dondero sr

    i have a 20 galon fish tank how many inches of media do i need in the growbed? right now i have only 4 inches .if i add another 4 inches is that enough?

    • TCLynx

      How big is the grow bed? Only 4 cubic inches? or is that 4 inches of media depth? or is the grow bed 4 inches by 4 inches with 4 inches of media in it?

      How many fish are you going to have in your system?
      Will your system have a sump tank?

      If you are simply pumping from your fish tank up to the media bed and having the media bed flood and drain back to the fish tank, you can only really have about 20 gallons of grow bed total to keep the fish tank from fluctuating too much, it will fluctuate if you do flood and drain.

      Only 4″ of media depth is a bit shallow for larger plants, what sort of plants do you want to grow? How deep is the bed? 12 inch deep grow beds are often recommended since it gives you lots of filtration while providing plenty of space for plant roots. Many people manage systems with shallower media beds but you have to be careful of large plant roots clogging the beds.

      I’m working on a book that might be of interest
      Aquaponics in a Nutshell

  • r dondero sr

    thanks for your answer i have 4 inches depth of grow bed media in a 19 gallon tote.if i add another 4 inches of depth is that suffecient,? also does the water need to drain dry or can some still lay in bottom like maybe 1/8 of a inch?only way i could get it real dry is poke some small holes to drain into fish tank. i don t have a sump tank only the fish tank and grow bed. i have it set so it pumps about 5 gallons into grow bed,from 20 gallon fish tank, i dont want to stress the fish

    • TCLynx

      Hum, so is 8″ of media enough? Hard for me to say since I don’t know how heavily you will be feeding the fish or how many fish (as in I don’t know how much filtration you NEED.) But as long as you are not growing corn, tomatoes and bananas in the tote, you will probably be ok with the shallow grow bed media depth. Just make sure you keep your flood height well below the top of the media (you want the top of your media to stay dry for the most part.)

      It is fine to have a little water remain in the bottom of the grow bed between flood cycles.

  • r dondero sr

    ok when i get more grow media i will adjust to keep top portion dry thank you

  • r dondero sr

    what does the timer flood cycle need to be set at? one hour? 1/2 hr?

    is it ok to turn syatem off at night? or must it stay on 24/7?

    • TCLynx

      The exact time for the flood cycle isn’t critical, the plants just need to be watered enough to stay moist and the bacteria just need to be watered often enough to stay moist.
      What is more important is that you need to run the pump enough to circulate enough water through the filtration (the gravel and the bacteria in the gravel) to keep the water quality good for the fish.
      If your system has very few fish for the tank volume and if you have supplemental aeration on over night or the weather is very cool, then turning the system off at night might be ok. I would advise doing some water tests first thing in the morning before turning the system back on to check and make sure ammonia isn’t building up in the fish tank in the time you are leaving it off. If you do get an ammonia reading higher than what it normally is when the pump is running (which shouldn’t be more than a trace if the system is properly balanced) then you need to run the pump more often.

      The rule of thumb is to circulate the volume of your fish tank each hour. So if you had say a 300 gallon fish tank and a pump that can only move 300 gallons per hour at the height of your grow beds, then you really should be running the pump all the time. If you are running a system where you will only run the pump for 15 minutes each hour, then you should get a pump that will move 300 gallons in 15 minutes at the height of your grow beds.
      The standard that many people use is to run the pump for 15 minutes each hour but that is mainly because there are timers out there with 15 minute increments. I have systems where I flood each bed for 10 minutes every two hours (but those are complex systems with 12 beds and automated valves and indexing valves so the pump is running constantly while the water all goes where I want it to.)

      And if you hate siphons and your pump is small so you can’t be turning it off and still get enough flow, then just leave the pump on 24/7 and run the beds constant flow/constant flood As long as the water level is below the top of the gravel so the surface stays dry, most plants like it just fine and so does the bacteria.

  • r dondero sr

    how deep must i plant roots? is two inches ok?or deeper? earlier you said not to allow water to reach top 2 inches i m confused

    • TCLynx

      Ok, the important things with media filled grow beds is you want the very top surface of the gravel to remain dry. How far below the surface of the gravel you can or should flood to will depend some on the particular gavel or media you use. Some media will wick moisture up quite far while others don’t wick much at all. Now if you are transplanting seedlings, dig down far enough so the roots will get some water when the bed floods. If you are planting small seeds, you might need to temporarily adjust your flood height so that the seeds will get enough moisture to germinate, once the seedlings are a bit bigger you can adjust your flood level back to normal.

      If you have a very porous media like hydroton, lava rock or growstones, then you probably won’t have the water flood as close to the surface but those media do tend to wick water up higher and there fore the roots above the flood level may still get some moisture. However, when planting seedlings, I would still make sure to plant them deep enough that at least some of their roots will be in water when it floods. If that means you need to plant so that some of the roots are down 4 or more inches, then plant that deep. If the seedlings are way to small to reach the flood level without being buried, then perhaps you need to temporarily adjust your flood height till the plants grow a bit.

  • r dondero sr

    thank you

  • I have a hydroponic 5 gallon bucket system that works quite well. I want to eliminate having to mix the nutrients. Can I water the buckets on a timer system rather than flooding. I can fill my present pump tank from the fish tank via float valve. Then the drain pipe from the buckets will go to a filter tank then pumped back to fish tank.

    • TCLynx

      As long as your hydroponic system isn’t going to cause problems chemically for your fish tank. I would personally want to make sure that all chemical fertilizers were well rinsed out of any hydroponics system and media very well before I would want to circulate my fish system water through it.

      The important part of converting a hydroponics system to use with Aquaponics is that you need to have plenty of bio-filteration so that the fish wastes can be converted to the plant usable nutrients and that you are circulating your fish water enough through this filtration to keep it healthy enough for your fish. You also need to make sure that things you use on/around your plants are totally fish safe (not all organic pesticides are fish safe) And if you use any aquarium medications, you need to make sure they will be safe for your food systems.

      Now as to watering buckets on a timer, as long as the reservoir/filter tank is big enough to handle the water level fluctuations that should be ok but I can’t make any guarantees since just a couple sentences about pumping from one tank and pumping from another and float valves doesn’t really tell me if you might be setting yourself up for an overflow or being pumped dry somewhere.

  • I have 2 fish tanks that I keep perch & catfish in. My current hydroponic system consist of 10 5 gallon buckets filled with perlite. I pump from the nutrient tank to irrigate from the top with 1/4 inch tubing on a designated timer setup. There is less than 2 inches of water in the buckets. It then flows back to the nutrient tank to recycle again. My question is if nutrients in the fish water will work as well as the commercial nutrients. I have on intention in this setup of pumping this back into the fish tank. I can replace the water I take from the fish tank with new well water. I don’t know if fish tank water measures the same as commercial nutrient water on the testing meter. I just want to take advantage of my fish water & not go through the mixing & monitoring of the commercial nutrients. If I decide to go larger scale, I would follow your advice to do so. thank you for your time & input.

    • TCLynx

      Fish tank water will NOT measure anything like commercial hydroponic nutrients. Commercial hydroponic nutrients are usually measured with some sort of EC meter which measures the electrical conductivity of the nutrient salts to estimate nutrient strength. Aquaponic nutrients are very different (more organic and not necessarily made up of salts that will measure on an EC meter anything like the levels one is used to for hydroponics) and most people use a freshwater aquarium test kit to measure the Nitrate levels of the fish tank water.

      I’m not saying that you can’t use your fish tank water for your hydroponics BUT it is not going to be the same, getting the right balance of nutrients is trickier and I’m not sure you can really expect to do it run to waste by simply taking your fish water and running it to the hydroponics and then topping up the fish tank water all the time. Might be possible but I don’t have a simply YES/NO answer for you since there are far too many parameters to figure out (what nutrients are in your source water, what sort of nutrient levels are in your fish system, what sort of filtration, what sort of fish feed, how much fish feed, what supplements would be required etc) from just a paragraph comment.

  • Narayan Kutty

    I am from India, in India Aquaponics is not that popular.I went for my first aquaponic system successfully.I have one question that
    can I use old/used roof tiles pieces 8-16mm size insted of Gravel.Roof tiles are made out of CLAY and available plentiful.It retains
    lots of water when it is wet.Please give your valuable advice’s.
    Thank you Sir,

    • TCLynx

      Provided there is nothing coating or used in the making of the roof tiles that would be toxic to fish or people then they would probably make a good media.

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