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PostPosted: Jan 27th, '11, 19:51 
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This has been touched on in many threads, but hear me out..

Some people here advocate that nitrates should be zero if your plants are doing their work.
Others feel the nitrates should be non-zero. More is better.. :headbang:

What do you say? :think:

I say that your nitrates should be at a steady level of between say 50 and 100ppm.
Why not zero? - IMHO, a zero reading shows that the plants ate all the nitrates that there was, and it follows that they could have had more.. Which means they are underfed. Don't know about you guys, but I want my plants to gorge themselves and eat and eat and grow FAT.

So a steady, medium level of nitrates shows that the plants are keeping up with nitrate production, (the levels are not constantly rising) and there is more than enough nitrates to go around. If nitrates start to rise, I can cut back on feeding. If the nitrates start to fall, I give more feed / and or add more fish..

Has anyone here done any scientific testing of different nitrate levels and the effect it has on plant growth? I would love to see some research that compares plant growth at say 20ppm against identical plants in an identical system with nitrates at say 150ppm..

My long term plan is to eventually decide (either through research or experimentation) on an ideal nitrate level, and then to create an electronic control system (I am an elec engineer, so this is sorta what I do) that would measure nitrate levels on the one end, and feed the fish on the other end. It will dynamically adjust feeding rates to control the nitrates to the ideal level. The system would have as an input the total weight of the fish in the tank, so it cannot overfeed the system, and the system would obviously need some sort of conversion leadtime programmed into it - basically the amount of time it expects the conversion of fish food to nitrates will take. The system will also have to keep an eye on nitrites and ammonia, because if the bio-filtration goes bust, more feed will not help.. In addition, if an HSM happens, the system will be able to perform emergency water changes in the case of catastrophic ammonia or nitrite levels. Lastly the system will also send me an HSM SMS in the case of anything newsworthy happening.

One huge problem with this is to electronically measure the nitrates, nitrites and ammonia.. There are devices that can measure these parameters, but this measurement lab is going to cost a good US$8500 on its own. Obviously if you are running a very big setup, $8500 is not that much to spend on something like this, but for me this is a backbreaker..

Does anyone know of any probe or sensor technology devices that can do nitrates/nitrites/ammonia?


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PostPosted: Jan 27th, '11, 22:01 
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Well sounds good, but I think you need to remember that aquaponics is about creating a balanced and sustainable system that mimics a natural system. And in nature, things are balanced and nitrates levels are kept to minimum levels naturally.

You sound like you are pushing for a hydroponics setup where you try to maintain a certain nitrate level for optimum production but probably at the expense of the poor fishes in the end...

There is one thing that jumps to mind that your electronic control system cannot account for... The build-up and breaking down of solids... the more you feed, the more solids need to be remove and broken down... It takes a while in a natural system for the solids to break down, hence if you keep pushing the system only from a nitrates level, your water quality may deteriorate and build-up of excess solids may become toxic... and may not even show a high enough ammonia reading for your US$8500 control system to detect... Fishes will start getting affected by the pollution in the water, and things like fin rot, ich, etc will start to come in...

And before you know it, HSM....

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PostPosted: Jan 27th, '11, 22:39 
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bassmonster wrote:
I say that your nitrates should be at a steady level of between say 50 and 100ppm.

Why???

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PostPosted: Jan 27th, '11, 23:06 
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I can see no benefit of plant growth when the nitrates are high as compared to when the nitrates are say 5-10 ppm. (Face it, if there is nitrate left, the plants have had all they need and didn't finish the rest, Does it make one grow better if you pile twice as much food on their plate even if they still only eat the same amount?) I would prefer if the nitrates in my systems stayed down below 40 since anything above that I can't tell the difference in color and it's all unreadable unless I do careful dilution tests.

And if one were to be removing solids to avoid the whole solids break down possibly overloading or clogging things and then feeding heavily to keep the nitrates high, well then I expect one would run into the too much nitrogen with not enough other stuff and have lots of weak vegetative growth and no fruiting/flowering.

In my estimation, such a project might be interesting (trying to get the electronics all working and being able to track all those things electronically and graph them on a computer) but it would not likely show any improved plant growth and definitely not to the point to balance the effort let alone the expense.

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PostPosted: Jan 28th, '11, 00:28 
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I think his point is....When your nitrates are at zero, how do you know that you are not limiting the plants growth? Could it take more in if say you kept a residual level of nitrates and never let it get to zero?

I personally havent seen a study on this in an aquaponic system so I couldnt say (but I would like to). Like BM said, it would take setting up independent systems side by side, with the same varieties, and closley monitoring the water parameters over a grow out period. We can guess but until somebody performs a scientific study, thats all it is.

There are just too many factors to influence the results in a backyard scenerio.

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PostPosted: Jan 28th, '11, 03:11 
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I wouldn't think solids build up would be an issue with worms in the grow beds since I doubt that the system would overfeed significantly. He's not shooting to have a continually rising Nitrate level just one that is steady, albeit somewhat higher than most of us would want to run.

Here is how to make your own Nitrate probes - http://escholarship.org/uc/item/9s44v89q#page-8
Looks like this is for a lab class - probes made in class might be available. Don't everyone write the email address but if you do lets hear about what you found out. You can also buy commercially made ones for about $180 US.

Apparently you hook the probe to a pH or ion meter which might have a computer output or you can skip the pH meter and just get one of these instead - ELIT Computer Interface/Ion Analyser

You can also get ion specific electrodes for other ions like ammonium and it looks like the tips on commercial ones can be changed if you wanted to experiment some.

You can probably get what you need for less than $1000. Still a hefty chunk of change but might even manage it for way less.


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PostPosted: Jan 28th, '11, 08:32 
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The advantage of having a higher nitrate reading - if you have to stop feeding for whatever reason, there is still nitrates for the plants, and it's easier to read the higher concentrations on the chart.

Higher nitrates cause no problems, and I am continuously trying to get any sort of nitrate reading in my system lol

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PostPosted: Jan 28th, '11, 11:42 
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Even if the research was worth doing you would need to repeat it for different crops.

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PostPosted: Jan 28th, '11, 12:22 
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One of the negative comments we get about AP and hydroponics is people talking about how plants are force fed. How plants can't just draw clean water when needed, it's always filled with nutrients. This force feeding, leads to week growth, week cell structure in the plant and higher susceptibility to pest and disease attack..

How true this is I have no idea...

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PostPosted: Jan 28th, '11, 14:17 
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too much nitrogen causes excessive growth in plants, which attracks aphids, mildew and other infections.

the other concern is nitrates are toxic, they cause numerous problems with the health of the aquatic animals. just because the animals don't drop dead immediately, i.e. nitrites and ammonia, keepers think they are safe, they aren't.

anyone concerned about their food fish being constantly existing in such a poluted enviorment. how much of the nitrates are absorbed by the fishes tissues that you plan on ingesting?


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PostPosted: Jan 28th, '11, 14:20 
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Sorry "rfeiller"... but nitrates have been found to only be toxic to fish... at levels exceeding 450+ppm...

And to my knowledge... "nitrates" aren't absorbed into fish flesh.... they do however, as in plants... form the basis of protein/flesh growth....

Welcome, by the way...

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Last edited by RupertofOZ on Jan 28th, '11, 14:23, edited 1 time in total.

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PostPosted: Jan 28th, '11, 14:23 
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And our aquaponic systems usually run with zero levels of ammonia... :wink:

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PostPosted: Jan 28th, '11, 14:38 
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what fish were you refering too, in my hatcherey i found that incorrect.


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PostPosted: Jan 28th, '11, 14:54 
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The only research I've been able to find during several years of aquaculture studies... refers to "Bluegill"... at around levels of 450ppm...

Can you point to any other research??...

Normally, most aquaponic systems run with nitrate levels between 0 - 30 .... very few above that, or for any length of time...

And I'm not sure why anyone, even within the context of this post... would want to run above those levels anyway... :dontknow:

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PostPosted: Jan 28th, '11, 14:57 
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P.S ... note your mention of a "hatchery"...

I have seen research that notes detremental effects of nitrate... on egg and fry developement... at levels around 150-200ppm...

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