Testing for K - The Planted Tank Forum
 
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post #1 of 5 (permalink) Old 08-09-2011, 12:01 AM Thread Starter
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Testing for K

Does anyone (besides me) test for potassium? What test do you use and What are your results?

I use the LaMotte tetraphenyl borate test modified so I can read the results in my Spec 20. (I know I am round and brown when it comes to testing). I try for 10 -20 ppm using this test.

If you play with chemicals you should know some chemisty.
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post #2 of 5 (permalink) Old 08-09-2011, 02:54 PM
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It's such an important nutrient but needed in such small amounts that I don't test and rarely add K only due to seeing a lack of K in plant leaves. But it sounds like a nice test kit!


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post #3 of 5 (permalink) Old 08-09-2011, 04:12 PM
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I did years ago.

A couple fo companies use to make test kits similar to Lamotte. Hanna makes a decent colorimeter, but you need to run standards to make sure the reagents they supply are correct(often they where off).

We also just did dilutions with dosing a known volume of water to estimate the K+, most do this since K+ is never critical typically unless limiting, which is 2ppm or less in most cases. 1-=20ppm is fine, but so is 30-50 or 100 + even.

Erik's winning AGA tank had well over 100ppm K+.

In the mid late 1990's even till around 2003, folks went wild with K+, but......there's also no need to lard it up that heavily and dosing it within say 10-30ppm is not difficult without a test kit.

K+ demand relative NO3 is roughly 1:4. So if you dose KNO3, unless you are supplying 75% or more N from fish waste or another source, it's unlikely you will ever experience K+ limitation.

That said, 1:1 K: NO3 seems common and there's no issues.
Uptake is lower/less than N generally but easier to track/account for than N.




Regards,
Tom Barr
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post #4 of 5 (permalink) Old 08-09-2011, 10:33 PM Thread Starter
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Quote:
Originally Posted by plantbrain View Post
I did years ago.

A couple fo companies use to make test kits similar to Lamotte. Hanna makes a decent colorimeter, but you need to run standards to make sure the reagents they supply are correct(often they where off).

We also just did dilutions with dosing a known volume of water to estimate the K+, most do this since K+ is never critical typically unless limiting, which is 2ppm or less in most cases. 1-=20ppm is fine, but so is 30-50 or 100 + even.

Erik's winning AGA tank had well over 100ppm K+.

In the mid late 1990's even till around 2003, folks went wild with K+, but......there's also no need to lard it up that heavily and dosing it within say 10-30ppm is not difficult without a test kit.

K+ demand relative NO3 is roughly 1:4. So if you dose KNO3, unless you are supplying 75% or more N from fish waste or another source, it's unlikely you will ever experience K+ limitation.

That said, 1:1 K: NO3 seems common and there's no issues.
Uptake is lower/less than N generally but easier to track/account for than N.
Actually, in three years, I've never had a problem with K. I've been testing to see if the old theory "Holes in your plants mean low K. I've never had low K but have had lots of problems with "holes in my plants." In every case the holes were caused by fish predation.

In fact, the absolutest biggest problem I've ever experienced (beside rapid plant growth) was fish predation. When you have rapid fast growing and very tender plants it is surprising what fish will take up vegetarian diets.

If you play with chemicals you should know some chemisty.
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post #5 of 5 (permalink) Old 08-09-2011, 11:33 PM
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Originally Posted by ray-the-pilot View Post
Actually, in three years, I've never had a problem with K. I've been testing to see if the old theory "Holes in your plants mean low K. I've never had low K but have had lots of problems with "holes in my plants." In every case the holes were caused by fish predation.

In fact, the absolutest biggest problem I've ever experienced (beside rapid plant growth) was fish predation. When you have rapid fast growing and very tender plants it is surprising what fish will take up vegetarian diets.
I agree, I've never been able to verify that claim myself either.
You could use Ca(NO3)2 in place of KNO3 to do this and test.
That should along with using say Fleet enema for PO4....be able to drive the K+ down fairly low.
Hopefully the tap is K+ free or you use RO.
I've never done it though.

Tasty tender leaves? That's what I'd eat, not the old tough yellow 1/2 dead ones, they have less nutritional value.

Older leaves have more periphyton however, which many species like to nibble on.

IME, poor CO2 causes most of holes etc.
Plants cannibalize themselves to keep growing at the tip in hopes of making it to the surface where there is ample CO2/light. It's a worth while sacrifice.




Regards,
Tom Barr
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