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PostPosted: May 24th, '18, 15:30 
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scotty435 wrote:
Can't help you as far as the kit and it's reliability. Most people don't test for potassium but someone here may have an idea for what the baseline is in their system. Plant needs for nutrients vary by plant type and life stage among other things. It's good to know that there's potassium in the system and I would think that if you have a reading it's probably OK but just having a reading doesn't really tell you if the potassium is available to the plants (I suspect a lot of it is though and it's probably existing as an ion) or if it's bound up in compounds where the plants can't access it. If it's available then the plants probably already have what they need and there is excess OR something is preventing the uptake of potassium. A lot of these tests can tell you something is present but not how much is available - it's not like hydroponics. Another thing that's different is that you're dosing with nutrients every time you feed the fish - in hydro you mix it once and let it go for a month. Hydro people may say you've got to have X amount of potassium but they aren't adding it the same way.


I just can't resist sticking my nose into this conversation because I've been struggling to understand what Scotty just said for some months now. Why can't we be a little like hydro people? If the fish are ok with their food, why not systematically add small amounts of deficient nutrients on a regular basis? And why aren't hydro people bedeviled with this, "Yeah, but is it available?" problem? :?:

Not being sarcastic or argumentative. Really hoping Scotty, or somebody can phrase it in a way that finally sinks into my thick skull. :support:


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PostPosted: May 25th, '18, 00:47 
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skilletlicker wrote:
If the fish are ok with their food, why not systematically add small amounts of deficient nutrients on a regular basis?


We do but we just have to figure it a bit differently. You see additions like this with iron and with seaweed which contains some potassium, some people alternate potassium and calcium additions when they adjust their pH but every system is a bit different so you have to figure what's needed for yours'.

Usually the chemicals that you'd add in hydroponics are pretty simple inorganic compounds and the nutrients wind up existing as ions in solution, which are relatively easy to measure with things like EC meters, and similar. In hydroponics, they carefully choose the inorganic compounds so that they don't get undesired chemical reactions. They also carefully control the pH to maintain the nutrients availability to the plants. At some point they toss the solution and start with a new batch because it's easier than trying to adjust the old one.

In AP you're building a biological system, your probably retaining and recirculating the water and you're going to get all sorts of reactions and interactions. In AP you get ions but then you also get complex organic compounds which aren't as easily measured and can't be taken up by plants without first being broken down. So lets say that your test destroys these organic compounds so that it can detect all the iron, magnesium or whatever that's in the sample - you get a result but some of that isn't actually available for use by the plants until it is broken down. Basically your plants could be starving and you'd only know it by looking at the plants, not by reading the test. Alternatively you could have a test that doesn't break down the organic molecules and doesn't detect the nutrients inside them but they are available to the plants (like a chelated iron product for example). Short of having a lab it's just easier and cheaper to watch the plants and adjust accordingly.

This website just talks about testing iron (some of this would apply to hydroponics) but it gives you an idea of how many different ways a nutrient like iron can exist and how some of the tests differ in what they detect - https://www.palintest.com/en/support/research-insight/iron-testing-which-method-use


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PostPosted: May 28th, '18, 06:19 
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Hi Ruicop,

i'm using this potassium test. Seems to work ok for me.
I have to dilute the sample because i have more than 20ppm. Usually i have around 60ppm potassium.

But there is no rule for the optimum concentration, it depends on the system. And especially on calcium and magnesium content. I think if you have too much calcium and/or magnesium it can interfere with potassium uptake.

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PostPosted: May 28th, '18, 11:00 
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Quote:
said for some months now. Why can't we be a little like hydro people? If the fish are ok with their food, why not systematically add small amounts of deficient nutrients on a regular basis? And why aren't hydro people bedeviled with this, "Yeah, but is it available?" problem? :?:



I'm no expert but I thought hydro techniques largely rely on dumping waste water when nutrients are out of balance. Then, starting over with known concentrations tailored to a particular plant and growth stage. This would be difficult with AP because of the large amounts of water needed to keep the fish. Also, hydroponics chemicals would kill fish (I think).

Sorry--just ready Scotty's post and he said this already.

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