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PostPosted: Nov 9th, '18, 05:59 
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Hi all,

I am done,
4 weeks calculation, google and every day a new result.. Anyone know the magic?

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This is my best (guess) outcome, but I am sure I missed the point somewhere

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Thanks for help

Will


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PostPosted: Nov 9th, '18, 12:06 
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That's a gravel volume of nearly 6,200L per GB, so my first question, before trying to figure out bell siphon sizing, would be: Why do you want the gravel beds so deep?...

300mm will do the job. It will halve the cost of your gravel bill, require bell siphons half the size, and consequently half the water flow (read as pump size/electricity costs).

Which leads me to my next question: Why such a large FT water volume?...

The total gravel volume (at 600mm GB depth) for the 12 gravel beds, is about 74,000L. With a 50mm dry layer it gives a total wet gravel volume of about 67,000L. With a safe Wet gravel:Fish ratio of 25L:1 (for edible fish to 500gm each), that gives a fish stocking capacity of about 2,680. Even with a generous 30L of water per fish, you could easily get away with about 80,000L of FT water volume.

Plus, I'm assuming the remaining 17 GB's are going to be DWC, so you really need to take the water volume of those into account. At the widely recommended 300mm water depth, it would be 3,090L ea, or about 52,500L. Add that to an 80,000L FT water volume and you have 132,500L, so a Wet Gravel:Water ratio of around 0.6:1, which is getting down into the lower end of where you would want it to be.

I can understand running deeper GB’s to give more bio-filtration per sqm, so the ability to run more fish and allow for the extra nutrient requirements of the DWC beds, but IMO, at some point it’s probably easier, cheaper and more desirable, especially in a system of this scale, to run 300mm deep gravel beds and achieve the extra biofiltration required through a tank or two of K1 media. This is how many commercial system are operated.

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PostPosted: Nov 10th, '18, 07:14 
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I imagine that the water will struggle to flow through the media to the giant siphon of such a large bed. The siphon would break through lack of flow before the bed was anywhere near empty. Especially when you get some roots in the media slowing the water flow further.

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PostPosted: Nov 10th, '18, 18:52 
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Hi,

I'm no expert in big systems, but i think this is a very bad idea to do so many large gravel filled growbeds.
Do you consider the time it will take when you will have to clean them ? (don't believe those who say media bed don't need cleaning).
Have you seen large commercial aquaponic farms ? They all use DWC with floating rafts. There is a reason for this...

You could do a few media beds, and a lot of DWC. And by the way +1 to Mr Damage stating that the FT is way too large.

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PostPosted: Nov 10th, '18, 22:22 
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Thanks for reply,

My thinking about this depth was creating more surface for bacteria,
River Gravel 20 - 25mm is very cheap here in Thailand and 6 cbm would be not exceeding 200 bucks per fill.

Got a mate from the water supply and he has always hand on Truck loads of 250 mm 2nd hand pipes. My Idea was perforate them laying them in and make sure there is a void space at the bottom for a boosts the flow rate.
These pipes would work also transport the compost worm crap on the bottom to the siphon before it becomes a solid layer of silt.


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