media or raft?

[Phil Treaster]

Hi, I'm starting up a system with a 150gl tank (just to start I'll add another tank if needed), my question is should I go with a media based grow bed or raft based? I've read that media based are more stable in small systems, is there some where on the big island to buy the Hydroton grow media?

Thanks for any help, Phil

[Christian James]

Use both, each has it's advantages and disadvantages but together they are fantastic.  Use cinder, red or black.

[Larry Yonashiro]

I've been running both systems for only 6 months now, but here's my take.  The media based flood and drain (ebb and flow) is faster and easier to get started, cheaper, and very stable, i.e., nitrogen cycle and water chemistry all looked good fairly quickly.  I would recommend this for the beginning/small urban aquaponics hobbyist farmer to get started.  The raft based system takes more design time and cost, more materials, more construction skills to build, and takes longer for the nitrogen cycle to establish, but I believe that it is more productive in the long run, i.e., more vegetables per square area.  There is also some discussion on this site about black versus red cinders, and the possibility of mercury content in the black.  I don't think there's anything conclusive yet.

[Phil Treaster]

Thanks for the info, I'm in construction so building the system is no problem, I plan on making my own grow beds and fiber glassing them. If I go media based I'll use Hydroton.

[Larry Yonashiro]

Good point.  I guess hydrotons would be the safe way to go.  You can get them at Ohana Greenhouse.

 

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[Chris Smith]

I use media beds as filtration for my raft systems. After growing with both methods I believe media is better for long term plants (like peppers or beans) and rafts are better for plants that are harvested in their entirety then replanted (like lettuce or bac choy).

You can get a bag of hydroton from Ohana Greenhouse for about $50. I get a cubic yard of black cinder loaded in my truck for the same $50. The black cinder is as light as hydroton and has WAY more surface area. The best thing about cinder is it is locally produced!! You can spend a small fortune on imported media or buy local.

If you would like to see some established systems a work, please come and check out our farm. We hold tours every Saturday and I can show how well integrated systems work.

http://www.coastviewaquaponics.com/

[Larry Yonashiro]

Chris, I'm in the process of incorporating a media bed in my raft system between the fish tank and my first trough, thanks to all the information that you've shared on this site.  It is built and lined, and plumbed.  I'm ready for the media - black or red cinders?  Can I get your opinion on the talk about mercury content in black cinders?  I've sent an inquiry to the folks at CTAHR, but no answer yet.  Side note: thanks also for your idea on the string hangers for vines on the troughs!  Worked out well.

Chris Smith said:

I use media beds as filtration for my raft systems. After growing with both methods I believe media is better for long term plants (like peppers or beans) and rafts are better for plants that are harvested in their entirety then replanted (like lettuce or bac choy).

You can get a bag of hydroton from Ohana Greenhouse for about $50. I get a cubic yard of black cinder loaded in my truck for the same $50. The black cinder is as light as hydroton and has WAY more surface area. The best thing about cinder is it is locally produced!! You can spend a small fortune on imported media or buy local.

If you would like to see some established systems a work, please come and check out our farm. We hold tours every Saturday and I can show how well integrated systems work.

http://www.coastviewaquaponics.com/

[Chris Smith]

Larry, I use black cinder because it is lighter than the red. Lots of it will actually float when I wash it. I am waiting on some info from the quarry. They said they have documentation on the cinder which possibly has an analysis. I was considering sending some to a lab to find exactly what is in it but do not know where send it.

[Larry Yonashiro]

Thanks, Chris.  I sent an inquiry on this to Dr. RuthEllen Klinger-Bowen who works with Clyde Tamaru at CTAHR, and can keep bugging her until I get a reply.  I wanted to know if any studies/information on this existed for Hawaii cinder, which I'm hoping will be different.  BTW, Clyde mentioned that Mari's Garden also installed an inline media bed to their raft system, but will take 5 years for it to mature (???).  He also mentioned that cinders from the Big Island is the best to use (has the most minerals) because it is the youngest island.  I did not know about the mercury claims back then.  Logic tells me that there is nothing to worry about with the black cinders because we live on it, and our drinking water filters through it.  There may be trace amounts of mercury, but within safe levels for drinking.  However, as Harold Sukhbir pointed out, there may be bio-magnification of methylmercury up the food chain.  I just want scientific verification on this from the UH.  So, I'll let you know when I get feedback.

[Larry Yonashiro]

Clyde is still waiting for test results for mercury and selenium on a fish from Mari's Garden (Fred Lau) which has a black cinder (from the Big Island) grow bed in line with his raft system.  As he mentions below, volcanoes are a major source of mercury (so its presence will show up in a lab test), but not in a harmful form for humans.  He also confirms the dangers of bio-magnification of methylmercury up the food chain, and also mentions an ongoing debate on the benefits of selenium which supposedly nullifies the effect of methylmercury in fish.

Selenium and mercury

 

From: Clyde Tamaru <[e-mail]>
Date: Wed, Jun 29, 2011 at 6:56 AM
Subject: Re: Fwd: Mercury in Lava Rocks
To: RuthEllen Klinger-Bowen <[e-mail]>

Hi RuthEllen and was wondering when this was going to rise to the top again.... I have the samples in the freezer waiting to be analyzed for both mercury and selenium that needs to be done soon. The tilapia are from Fred's place so from systems that are using the cinder bed. However, have to point out that the mercury in the cinder is the elemental mercury that does not pose any harm to humans. In fact it is the same form of mercury that are used in dental fillings. Ask someone if they have silver fillings in their teeth and that contains more than just silver. That's right it also contains mercury albeit in a form that does not do harm. Volanoes are a natural source of mercury and hence it will be in the cinder but in a form that will not do us any harm......

The one that is a problem is the methylated or methylmercury that is made after the microbes work on the elemental form. THis is the one that bioaccumulates in the tissue of organisms and travels up the food chain. That is why large or fish that have an extended life history are the ones that have higher amounts. However, it should also be pointed out that there is a lot of dispute that even those amounts are not harmful to humans and there is a website that explains this a bit more.

C:\Documents and Settings\Clyde Tamaru\My Documents\NOAA Seafood Safety 2010 Mercury Selenium Proposal\Selenium Mercury's Magnet.mht

The folks who are following this closely in Hawaii have also indicated that you have to take into account the amount of selenium in the fish as this element counter acts what methyl mercury does.. Hope this helps and will have data to share shortly. However, have to say that I am sure that it will not be a concern...

Clyde S. Tamaru
Aquaculture Specialist
College of Tropical Agriculture and Human Resources
Department of Molecular Biosciences and Bioengineering
1955 East-West Road, Ag. Science 218
Honolulu, HI 96822
Phone: [phone]
email: [e-mail]

[Phil Treaster]

I see that you wash it, do you all so screen out the fine dust so it does not get into the fish tank, if so what size screen do you use? I'm almost  finished building my first bed, I may line it with food grade catchment water tank liner instead of fiberglass, what do you think?  Thanks for all your help, Phil

Chris Smith said:

Larry, I use black cinder because it is lighter than the red. Lots of it will actually float when I wash it. I am waiting on some info from the quarry. They said they have documentation on the cinder which possibly has an analysis. I was considering sending some to a lab to find exactly what is in it but do not know where send it.

[Chris Smith]

Great info Larry. I look foreword to the test results.

Phil,I screen wash my cinder. I use a 1/4 mesh with lets the small rock, sand and silt out of the bigger rock. I use the large rock directly in the gravel beds. I like to leave a little grit on the big rock for the worms to use in their stomachs. I re-screen the small stuff with window screen to remove the small rock from the sand and silt. I use the small rock for seeding and I grow carrots in the leftover sand.

[Chris Smith]

Hey Larry, is there any test results on the tilapia from Fred's yet??