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PostPosted: Nov 7th, '10, 15:36 
I take the point of what you're saying Scotty....

But the minimum oxygen requirement factor would no doubt incorporate a "worse case" type scenario... including temperatures approaching, or exceeding a species upper limits...

That doesn't mean that such has been quantified within then formula for any specific species, particularly trout...

Primarily because from a aquaculture perspective... it would be assumed that you wouldn't be running a species above it's accepted temperature tolerances....

In such cases as trout... you have three options... and I've employed them all successfully...

Reduce the water temperature... reduce/stop feeding.... increase oxygenation...

All three options modify the outcome of the formula... but the base requirements for oxygenation and filtration still exist as a minimum....

As Stuart says... to go beyond a "generalised" tool... would require multiple thesis.... probably specific to each species... and varibles such as altitude and barometric pressure...


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PostPosted: Nov 7th, '10, 21:01 
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I would love to see a study done on O2 drop over time within flooded and various draning regimes relative to stocking densities.

Such a study would really nail down a number of design and operation criteria or show that it does not matter that much.
I know a lot of people say that it dosnt make any difference but in commercial production a 1% increase can mean a lot more than that in profit.

Also getting a better handle on the O2 demands of mature GBs would be a good thing. Eco fortura worked out that the O2 requirements of their bacteria was equal to half that of the fish. However that was with solids seperation and removal. GBs would need more than that for everything else that grows in them.

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PostPosted: Nov 7th, '10, 21:54 
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TCLynx wrote:
stuff deleted ...ctions pdf, it is basically telling me that I've got only 1/6th of the gravel square footage that I need and that for this to work I need to be cleaning the solids out of my gravel every 3 or so months?

So, if this tool were absolutely right, my system shouldn't be working much at all.

...stuff deleted...


one of the problems with measuring the surface area of stuff is that it depends on the length of the stick you use to measure it with.

If you have a square island that is a square mile according to a satellite map, the coast guard will say the shore line is 4 miles long. A person walking the high tide mark collecting blue barrels that have been dumped into the ocean by thoughtful cola companies might walk 50 miles to go around the squiggly line around the beach, and a micro beastie walking over the sand particles might have to cover a few thousand miles to get around the same island. The mountain ranges are pretty high when you are a micro beasty, and the high tide mark weaves in and out of those mountain ranges.

The surface area available to bacteria to colonize depends on which lens you have used as the eyepeice on your microscope rather than on a tape measure.

All other things being equal, the equation is really ((pleasant(not too wet, not too dry, not too hot, not too cold,X only knows what micro beasties like)) micro beasty real estate) : (nutrient input @ fish metabolic rate) / ((blah)*(pH + what was the question again?)) - (protein / flavour)

I think you should just rest assured that it's been proven beyond reasonable doubt that your system simply doesn't support life and you should go back to buying those yummy tomatoes and strawberries with the white plastic-like stuff inside that keeps them fresh in transport :)

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PostPosted: Nov 7th, '10, 22:14 
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Perhaps part of my problem was that the Imperial Version of the design too, seems to be an afterthought and the notes for it are still partially in metric and it isn't clear which gallons are in use. So, my low grade is for the imperial tool.

To really test my system against the metric tool would actually require quite a lot of conversions and since my beds are not rectangular a lot of estimation to figure out what the square meters of area would be. I don't think I'm going there right now.

And since the research that actually supports this tool has mostly been done on a tropical island and mostly where raft culture is the favored means. I guess we shouldn't really expect them to suddenly start testing all different depths of gravel beds and importing worms to test them. If we want that scientific data, well we probably need to fund those trials ourselves or find another university to do it.

I know that deep flood and drain gravel beds with worms work better than what the tool says but I don't have any university research to back that up. Doesn't mean it doesn't work.

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PostPosted: Nov 7th, '10, 22:17 
Indeed TCL.... and there's only been one person I know... that has said that such systems don't work.... :wink:


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PostPosted: Nov 8th, '10, 02:21 
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What about taking a tall narrow column and filling it with your medium of choice. Break it in by having it attached to your fish tank so that it can get established with the typical load of bacteria for the nitrogen cycle then disconnect it and hook it to a tank of water where you can add known amounts of ammonia or other nitrogen source. Starting with flooding all the way to the top, cycle (flood and drain) the system until all the ammonia has dissappeared - count the cycles and you should be able to quantify the conversion rate. Repeat this process with shallower flood cycles and you should end up with an idea of conversion rates for different bed depths. With some work the surface area of any given media can probably be related to the amount of water it displaces in a graduated cylinder. But for this experiment it is easiest to use roughly spherical expanded clay balls. From math we know that the formula for a sphere are
Surface area = 4πr2
Volume = 4/3πr3
This would just be an estimate because the clay balls are porous but it might be close enough. We might also be able to correct for the difference by measuring the volume of water displaced by a clay ball dropped into a small graduated cylinder and then comparing calculated volume, area, and measured volume to solve for the unknown area of the clay ball.

Any thoughts?


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PostPosted: Nov 8th, '10, 02:30 
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Waited to long to add this to the last post - You should also be able to approximate the surface area of other media based on their conversion rates.


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PostPosted: Nov 8th, '10, 03:02 
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I don't expect that anyone is really questioning the accuracy of the model's bio-filter recommendations and simply testing the ammonia conversion through a tall filter may prove interesting and provide some useful info, but, I don't think it will answer the question that is most pressing in my mind at least. Which is to do with the solids handling capacity of deeper beds.

I think the draw down of aeration into flood and drain beds actually handles solids in more than just the top few inches of media. I know I've heard many proponents of deeper gravel beds note improved solids handling with the deeper beds but this has mostly been just observational and without any side by side controlled experiments done. I know I don't currently have the space or money to set up two side by side systems with equal amounts of media only one with deep beds and the other with shallow beds to compare. It also takes a far longer time to really judge the solids handing capacity since problems are rarely evident on that score through the first season unless stocking is way beyond reason.

Hum, so how to test such a thing on a smaller scale than a whole system?
Anyone have any ideas about how best to compare different depths and how they handle solids?

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PostPosted: Nov 8th, '10, 04:56 
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No reason you couldn't run your system water through a pair of pipes filled with media before it goes into a grow bed. One inflow at the top of each pipe and two outflows for each - the normal outflow would exit above the bottom using a loop siphon and the test outflow would be directly from the bottom.

When you've run it long enough just drain out the test outflow into a container and follow the following procedure for determining Total Suspended solids

http://www.ecy.wa.gov/programs/wq/plant ... /4tss.html.

You'd need an very accurate balance and it would be better if you had more columns but this would give you a ballpark estimate.

My guess is we wouldn't care about Total Dissolved Solids which would include salts but this can be tested with a conductivity meter if desired.

OR

Both TDS and TSS could be done by a lab for about ten dollars each. The samples would need to be transported properly for the test to be valid.


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PostPosted: Nov 8th, '10, 05:47 
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Scotty, I don't think it is the dissolved stuff that is the problem people tend to focus on for the solids in the grow beds. The "problem" that most people focus on about media filled grow beds is the idea that they require being cleaned out because of an excessive build up of solids.

Here is a quote from the PDF that goes with the tool.

Quote:
Whilst the model does output a size for the media bed to meet all the mineralisation requirements of
the solid fish waste produced, it is also highly recommended that a media bed maintenance approach
be used for your home system, especially when fish densities above 5 kg/m3 are employed. Media
bed maintenance consists of cleaning the media by gently washing it in system water to remove any
accumulated solids. This should be done once every 3 – 6 months, depending on the fish stocking
density; higher densities should have more regular cleaning. Using system water allows you to
maintain the bacteria on the surface of the media without affecting it. Do not use any chemicals
or detergents to clean your media. This cleaning operation can often be performed by using a
“gravel vacuum”, which allows cleaning without removal of the media from the bed.


I'm wondering how one might be able to test for a dangerous build up of solids so one could a-be able to monitor that and react before it gets to a "dangerous point" and b-have a test that would be useful when running experiments to see what depth of bed takes care of mineralization best without risks of anaerobic areas. The argument against deep beds being that the lower portions will become anaerobic as solids build up.

The only grow beds I've had problems with clogging were actually more a root clogging problem or with the really badly clogged one it was less than 10 gallons, shallow and getting all the flow from a rather large gunky fish tank (duckweed pee ponics.)

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PostPosted: Nov 8th, '10, 12:48 
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You're right I didn't understand what you were after. In my opinion growbeds don't really need cleaning very often, if ever, when you have worms in a flood and drain system because the media is rinsed with every cycle (my experience is limited to 2 years without cleaning) and the worms handle the big stuff.

I don't see any obvious way of getting an early warning. You could use a pipette or tube to take water samples from the bottom of your system just to see if it is anaerobic. From the sound of it you aren't having any issues with this anyway

I would sure love to have a DO meter to measure the mg/l of DO in a heavily loaded system as water -
1. exits the pipe to the growbed.
2. reaches the bottom of the growbed beneath the pipe.
3. reaches the other side on the bottom of the growbed. If there is any O2 left here you probably don't have a mineralization problem.

Even if the bed is anaerobic couldn't a person just aerate the water going into the growbed or put bubblers down in the growbed? I would think this would end any issues.


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PostPosted: Nov 8th, '10, 13:30 
With proper stocking rates... and more particularly, the right amount of growbed filtration capacity and oxygenation for the number of fish and feed rate....

The grow beds, with worms.... just wont develop "anaerobic" zones... or require cleaning....

And DO measurements of flood & drain systems have been shown to provide adequate levels of oxygenation by design.... although we recommend adding supplementary aeration....

The tool has underlying values for DO incorporated into the formula...

Use the tool to size your system design, and stock accordingly.... and in conjunction with worms in your grow bed...

You wont have a problem.... and that's what we've been on about for years...


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PostPosted: Nov 8th, '10, 13:54 
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So if you have less surface area than the tool calls for but more depth yet you have worms in the bed you should be ok as long as it's flood and drain. The notes (except for the worm part)for the tool would indicate this at least, even if the model doesn't really let you stretch your growbed down instead of out.


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PostPosted: Nov 8th, '10, 15:03 
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I dont think we need to worry too much about surface area of the media becuase even the UVI sytem with no gravel had enough surface area for nitrification. Surface area is a concern in AQ becuase they are trying to minimise the size of bio filters.

The surface area that is important for a balanced system is the growing area. The volume of the gbs is important so that there is enough space to retain/store the solids and provide a habitat for the beasties that eat them.

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PostPosted: Nov 8th, '10, 15:09 
scotty435 wrote:
So if you have less surface area than the tool calls for but more depth yet you have worms in the bed you should be ok as long as it's flood and drain. The notes (except for the worm part)for the tool would indicate this at least, even if the model doesn't really let you stretch your growbed down instead of out.

Experience of many members would seem to confirm that Scotty....


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