System design

[Sylvia Bernstein]

What are your thoughts on system design?  Media vs raft.  Deep media beds vs shallow.  Siphons vs timers.  Tell us your thoughts and let's get the conversation rolling

[David S.]

Component ratios and sizing are the problems I am wondering about right now. How do I know how much raft surface area I need in order to use up all the nutrients that I will be adding to the system. This is the system I am thinking about building:

Two 300 gallon fish tanks. One 300 gallon clarifier. One 55 gallon filter, and then the hydroponics system.

I have read that you need around 57 grams of fish feed/ m^2 of raft. Surely this depends upon the density you are planning on stocking your tanks at (I am planning for .25 lb/ gallon), and the volume of water in your system. I assumed that since the 57 g/ m^2 was based on a .5 lb/ gallon stocking density, I would need half the surface area, or 114 g/ m^2 of raft surface area.

Any help on sizing ratios would be helpful.

Thanks,
David

[Sylvia Bernstein]

Rebecca is our raft system guru...

[David S.]

What is your system like? Did you spend a lot of time on the design, or did you just go for it? I am prone to lots of designing. I have two books on raising fish. 1) Rebecca Nelson's Aquaponic Food Production, and 2) Timmons' Recirculating Aquaculture. The last chapter in the 2nd book is strictly about aquaponics, and was written by the woman who runs the University of the Virgin Islands commercial sized system.

I should have some drawings of my system soon, and I just picked up some used parts today.
David

[Jonathan Hanridge]

Sorry David, can't help with sizing ratios as I'm just a wannabee/lurker but curious as to why you chose a raft system over media based? I can't decide which would be easier/better and they both appear to work well so I'm at a loss for even beginning to try to make that decision. What made you go with raft?

David S. said:

Component ratios and sizing are the problems I am wondering about right now. How do I know how much raft surface area I need in order to use up all the nutrients that I will be adding to the system. This is the system I am thinking about building:

Two 300 gallon fish tanks. One 300 gallon clarifier. One 55 gallon filter, and then the hydroponics system.

I have read that you need around 57 grams of fish feed/ m^2 of raft. Surely this depends upon the density you are planning on stocking your tanks at (I am planning for .25 lb/ gallon), and the volume of water in your system. I assumed that since the 57 g/ m^2 was based on a .5 lb/ gallon stocking density, I would need half the surface area, or 114 g/ m^2 of raft surface area.

Any help on sizing ratios would be helpful.

Thanks,
David

[Jonathan Hanridge]

If I went with a media based system, what would be the best media. I imagine where I live the CHEAPEST media I could get would be cinder rock. I know from ordering it for my driveway it comes in many sizes from 3 inches all the way down to cinder sand. I imagine the smallest size is probably 1/4 to 1/2 inch (screened). This would be about the same as pea gravel, maybe slightly larger. It has much more surface area for bacteria to colonize and the inherent porosity of the rock makes it light also. A little sharp on the hands maybe. I'd have to wash it well before placing it in grow tubs. Anyone ever use this? What would be possible drawbacks?
My friend has a pool that is 18' diameter by 48' tall that she got at Wal-Mart for about $300. It's made by Intex. I called them to ask about pumps. Their biggest one is rated at 2500 GPH. The pump sits on the ground and pumps the outflow water back into the pool at about 3 1/2 ft height. It goes through a filter cartridge first but the guy said the pump would run without the filter cartridge installed. Could this work for Aquaponics. My friends pool would hold something like 5000+ gallons. I calculated at .25lb/fish per gallon you could have something like 700 full size Tilapia. Don't know how to calculate square feet of grow beds per lb. of fish (What is that, by the way?) This sounds like way to big a system and I have no desire to commercially farm produce or fish but I can't help but think that a smaller pool might work for the fish part of the equation and then could you swap out a bigger pump for the one that comes with the pool? Any ideas?

[David S.]

That is quote a post. That is a pretty big pool, and you are going to raising a lot of fish. Unless you want to spend a fair amount of money and time to make this work, I would start with a smaller pool.

I am not sure what your cinder block is made of, but I would be careful with that if it is made with concrete. A lot of cement in concrete now contains fly ash, which is a waste product from burning coal. As you might imagine, it contains a lot of heavy metals. The concrete is a stable form with which to store fly ash, but I don't know if I would eat something that was grown in it if I had another choice. Other cheap forms of media are packing pellets made of styrafoam, coarse sponges (such as the ones used for cleaning), or just crushed gravel.


The ratio of weight of food/ area of grow bed depends on what type of hydroponics system you are going to be using. I used the 0.25 lb of fish/ gallon of water because it is a good level for beginners that are using a raft system (myself included). I still don't really know how to size a hydroponics raft. If you are raising fish at 0.5 lb/ gallon, then the ratio is somewhere between 60 to 100 grams of fish food/ (day*m^2 of raft). Lets say you plan on having 750 lb of fish in your 5000 gallon tank, then you would need to feed them around 1.5% of their body weight per day for them to grow, which means you are feeding them 11.25 lb of fish feed per day when they are fully grown. That's a lot of food.

According to my calculations, I need a flow rate of about 10 gpm (600 gph) when my tank is fully stocked, which is based on a loading rate of 2 kg/(Liters*min). If your fish tank is 8.33 times larger than mine (5000 gallons/ 600 gallons), and you are using the same loading rate, then you would need a pump that pumps 4,800 gph.

Loading rate - (L) is fish mass per unit of flowing water (kg/Lpm)

I would also check the math on the size of your pool.

Volume = pi()*18^2*3.5/4= 890.6 ft^3 , this leaves you 6" of freeboard. If you convert this to gallons, assuming 1 gallon= 0.1333 ft^3, then your pool is actually about 6,700 gallons.

Here are some good websites for aquaponics.

Good luck,
David

http://attra.ncat.org/new_pubs/attra-pub/aquaponic.html?id=Texas
http://affnan-aquaponics.blogspot.com/
http://srac.tamu.edu/ - This website has some great free technical information on aquaculture

[Emma Lysyk]

Jonathan,

I would heed David's warning about the rock material. Fish are severely sensitive to lots of metals including lead, nickel, and copper. You might try checking to see if there's a hydroponics shop near you, otherwise I know Sea of Green ships (unless you want to drive into Phoenix). Another medium would be aquarium gravel. I saw at a Lowe's here bags of river rock for about $5, but you would need to wash them thoroughly without soap and make sure they aren't chemically treated.

One of the ladies at Petsmart has suggested that I rinse them clean, then soak them in a chlorine bleach and water solution (1 capfull per gallon). Then drain the solution, fill the container back up with water and treat with water conditioner to remove the chlorine and rinse again.

Another option is Perlite. I wouldn't use Miracle Gro's version since it has ammonia phosphate and ammonia nitrate added to it, but maybe a hardware store nearby has some. It's a puffed volcanic glass. Vermiculite works the same way. I would try for an organic one.

I've settled for Hydroton that I got from Sea of Green. It was $35 for a 50 liter bag, which is much cheaper than aquarium gravel, and I didn't have to stress out over whether or not the rocks would have something on them that would hurt my fish.

As for growing space, I've heard 1 square foot per half inch of fish works, and you don't want any more inches of fish that you have gallons of water. The exception of this is for large fish, where you get to start calculating their width, too.

I'd start with a smaller pool - no bigger than a large bathtub - for your first system.

You're welcome to peruse my saved bookmarks here: http://delicious.com/emacartoon/aquaponics but, specifically, you might like this blog: http://athoughtadrift.com/gemmell/category/aquaponics/

[Jonathan Hanridge]

1. What was your rationale for going with a raft system for your Grow Beds rather than a Media based system (i.e why did you choose a raft system)?

2. Cinder ROCK, not cinder block, not a byproduct, ancient pyroclastic extruded basalt ejected from volcanoes. No cement, not manmade. Found this online to help you understand:

Lava Rock (Cinder rock) is a lightweight decorative rock popular in today’s natural landscapes seeking low maintenance. The vibrant colors complement and help contrast landscaping elements such as shrubs, grasses and flowers. Being lightweight, Lava Rock is easy to apply. It’s durability offers a lasting alternative to beauty bark yet Lava Rock can help maintain soil humidity without attracting insects.

Lava Rock was “created in Nature’s own furnace . . . spewed forth in a magnificent display of red boulders, sand and gravel deep within the earth. This rare product comes to us in a way that man has not been able to duplicate.” According to mineralogists at Oregon State University, Lava Rock resulted when steam rose through a volcanic cinder pit after an eruption. Enough silica dissolved in it to deposit opal on the surface of large bubbles that formed before the cinders solidified. Non-precious opal is made of silica, oxygen and water. The ovaline formed before the eruption and is surrounded by the later forming cinder material.

Mineral Content

Nitrate Nitrogen.................................4.0 p.p.m.
Phosphorus........................................6.0 p.p.m.
Potassium.........................................59.0 p.p.m.
Zinc.........................................................6 p.p.m.
Iron..................................................10.0+ p.p.m.
Copper...............................................5.5+ p.p.m.
Magnesium.......................................2.0+ p.p.m.
Boron.................................................10.0 p.p.m.
Sulfate.................................................7.0 p.p.m.
Organic Material...........................................5%
PH.........................................................8.2 Units
Calcium..................................1.3 Meq/100 gm*
Manganese...........................0.6 Meq/100 gm*
Sodium...................................0.1 Meq/100 gm*
Cation Exchange Capacity..3.2 Meq/100 gm*
* Milli-Equivalent per 100 grams


Looks like pH is too high. Don't know how they got this figure. I can get 15 cubic yards of 3/8 inch to 1/8 inch delivered to my door for $206.74. The extra can be spread on my driveway and entrance roads. I will wash it good and then test a bunch in a 5 gallon bucket with a ph test kit over a few days to see what I get.

3. Don't have a pool, just used friends as example, decided also that was too big! Is loading rate same for a media based ebb and flow system?

4. Pump GPH rating is for a specified height also. Flow decreases rapidly as you raise head and pump has to work harder too. What is most durable, longest lasting pump, ideally high volume, low energy usage and low price. Dang, that whole gravity thing really gets in the way here!

[Emma Lysyk]

Weird, I've never heard of lava rock being referred to as cinder rock. That should work fine, actually. Just make sure you rinse it well :) The listed pH is of the rock itself, so its dust might raise the pH a little, but most rocks are basic as opposed to acidic, and should be fine.

I still don't understand the ratios for GPH to pump height, but I know my 30 - 50 GPH went about a foot above the water, and my Eco 132 should go about 3.2 feet. I got the dinky one from Lowe's for about $20, and my low-power Eco 132 from Sea of Green (www.sea-of-green.com/eco-plus-water-pumps.html) for $11.48. The page I linked has a chart of their capabilities.

I went with a growing medium instead of rafts, so I can't help you there.

[David S.]

I have never heard of lava rock being refered to as cinder rock either. It should work well. It has a good surface area to volume ratio. It seemed expesive when I looked at it at a landscaping supply center, however I have not done much shopping for media yet.

I am impressed that the sea of green website has performance curves for their pumps. To use those graphs you need to know how much energy loss their is in between where you are taking the water from and where the water is going to, which, as Jonathan said, depends on how much water you want to pump and what you are pumping it through. The name of the graph you need to properly use those pump performance curves are called system performance curves. It is basically a plot of how much energy your design will lose based on how much water you are pumping. You plot both of those graphs on the same plot, and their intersection defines how much water your pump will move and how high that water will go.

Jonathan - I have no idea what the "most durable, longest lasting pump, ideally high volume, low energy usage and low price" pump is. lol! That is a lot of criteria, but they are the right ones.

As far as comparing raft grow beds to media filled grow beds, here is what Dr. James E. Rakocy has to say about them: Bad: 1) subject to clogging, 2) roots of plants are left in system after harvest. 3) Cleaning gravel is difficult. 4) Very heavy
Good: 1) No need for a seperate filter. 2) Easy to build with. 3) Can provide some nutrients to plants

Raft Hydroponics
Bad: 1) Plant roots are more susceptible to harmful organisms associated with aquaculture. ie: fish fry, snails. 2) Solids must be removed before raft system
Good: 1) Avoids clogging 2) Minimizes algae growth by shading water. 3) Rafts (just styrafoam) are easily moved and cleaned. 4) Ligth weight when compared to rocks.

That is a summary from Recirculating Aquaculture, by MB Timmons and HM Ebeling.
I have not decided which system I am going to go with, although after putting together that list I am inclined to go with a raft system.

David

[Jonathan Hanridge]

Another plus for Raft: you could raise Giant Malaysian River Prawns under the rafts. They don't eat the plant roots and they look really cool!

David S. said:

I have never heard of lava rock being refered to as cinder rock either. It should work well. It has a good surface area to volume ratio. It seemed expesive when I looked at it at a landscaping supply center, however I have not done much shopping for media yet.

I am impressed that the sea of green website has performance curves for their pumps. To use those graphs you need to know how much energy loss their is in between where you are taking the water from and where the water is going to, which, as Jonathan said, depends on how much water you want to pump and what you are pumping it through. The name of the graph you need to properly use those pump performance curves are called system performance curves. It is basically a plot of how much energy your design will lose based on how much water you are pumping. You plot both of those graphs on the same plot, and their intersection defines how much water your pump will move and how high that water will go.

Jonathan - I have no idea what the "most durable, longest lasting pump, ideally high volume, low energy usage and low price" pump is. lol! That is a lot of criteria, but they are the right ones.

As far as comparing raft grow beds to media filled grow beds, here is what Dr. James E. Rakocy has to say about them: Bad: 1) subject to clogging, 2) roots of plants are left in system after harvest. 3) Cleaning gravel is difficult. 4) Very heavy
Good: 1) No need for a seperate filter. 2) Easy to build with. 3) Can provide some nutrients to plants

Raft Hydroponics
Bad: 1) Plant roots are more susceptible to harmful organisms associated with aquaculture. ie: fish fry, snails. 2) Solids must be removed before raft system
Good: 1) Avoids clogging 2) Minimizes algae growth by shading water. 3) Rafts (just styrafoam) are easily moved and cleaned. 4) Ligth weight when compared to rocks.

That is a summary from Recirculating Aquaculture, by MB Timmons and HM Ebeling.
I have not decided which system I am going to go with, although after putting together that list I am inclined to go with a raft system.

David

[Sylvia Bernstein]

hey guys, I wanted to jump in here and offer another vantage point on raft vs. media, if I may. Over the past 5 days I've had the privilege of having long conversations with both Dr. Rakocy (an interview for Backyard Aquaponics magazine) and Travis Hughey, the Barellponics guru. Dr. Rakocy's focus was exclusively on developing commercial growing systems that could optimize both fish production and plant production. He is actually amazed that home-based aquaponics is taking off like it is, but definitely agrees that media based systems are the better way to go for a hobbyist. Rafts are more complex to set up (need clarifiers, etc.) and operate (daily cleaning), and they are limited in what you can grow - not really designed for long term crops (think tomatoes here) or subterranians (carrots, onions). But they are great for producing load of fish because you remove the solids...but the solids are needed to provide the more complex micronutrients needed by longer term plants. Contrary to some opinion, you do not need to clean out media based systems. Joel Malcom ov Backyard aquaponics has never cleaned out his, and it has been running over 6 years. Travis Hughey says that he occassionally cleans out his, but mainly because he lives in a remote, wooded, Southern area and worries about extra critters getting in there (snails, bird poop, etc). What most do is if they see a solids buildup they just throw in some redworms and let them go to town. The problem in this very, very young community of aquaponics is that most all of the academic research has been done on creating commercial systems (guess who pays for research grants...) and it just doesn't always apply to the needs of a hobby grower. My 2 cents....hope this helps.