Help me understand Potassium - The Planted Tank Forum
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post #1 of 42 (permalink) Old 05-29-2015, 11:59 PM Thread Starter
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Help me understand Potassium

I don't have a way to test potassium.

The basis of my question is, whether there is any guidance as to how fast Potassium is consumed in a moderately planted tank.

Here's the story:

Some time ago I had signs of potassium deficiency (pinholes in annubias) when I was adding none (only in water change), and did some math at the time, and started adding it daily at roughly the PPS-PRO rate (I thought).

Now (months later) I have some symptoms that looked like potassium toxicity, so I reran all the calculations myself (the current version of the calculator I used is broken), and found I am adding about 1.4g of potassium daily, and I think PPS-PRO calls for 1.01g daily (weights are elemental K).

But then I looked at Equilibrium. In each water change (about 80G) I add about 128gm of Equilibrium, which is (per Seachem) 19.5% potassium. If I did the math right, that means my 80G of water is at 70ppm potassium (25g K) in each water change, which was surprisingly high. In fact that seemed a bit high in general (but it's only dGH=6 as a target).

And while I am aiming for monthly water changes it's been more like every 2-3 weeks based on nitrate levels.

Here's my question: In what I would call moderately planted, no CO2, how fast does Potassium get used?

Is it possible I'm reaching toxic or damaging levels between Equilibrium and daily dosing?

I was just going to buy a kit, but didn't see a fresh water version (saltwater kits seem only good for high levels like 150+).

Is there really a chance I'm over-dosing?

Does the math seem right?

Linwood

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post #2 of 42 (permalink) Old 05-30-2015, 03:03 AM
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Potassium to me is a black box macro. I'm in same boat as you and I need to know my own levels as well.
Lamotte freshwater 0-50 ppm test kit is in the mail, but they run about $80 shipped.
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post #3 of 42 (permalink) Old 05-30-2015, 10:00 AM
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I'm about to get around to sending a water sample to a nearby lab.... $22.50 to have potassium (and the other black box solutes at the same time, Ca and Mg) done.
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post #4 of 42 (permalink) Old 05-30-2015, 02:25 PM Thread Starter
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Originally Posted by Xirxes View Post
Potassium to me is a black box macro. I'm in same boat as you and I need to know my own levels as well.
Lamotte freshwater 0-50 ppm test kit is in the mail, but they run about $80 shipped.
Where did you find one? When I look at their site I do not see a "K":

http://www.lamotte.com/en/aquarium-f...dual-test-kits

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post #5 of 42 (permalink) Old 05-30-2015, 06:33 PM
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post #6 of 42 (permalink) Old 05-30-2015, 07:41 PM Thread Starter
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Thanks, didn't look there. If you get a chance, please report back how it worked, and what you determined. And if it has an expiration date! While I hate to pay that for a test kit, it would be easier to stomach if it was good for many years.

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post #7 of 42 (permalink) Old 06-06-2015, 05:02 AM
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Since my last post, i did a 80% water change, then went 4 days with zero dosing of any kind, only to start 1.5gram of CSM+B and 1.5gram K2SO4 daily wednesday, thursday and 5gram CSM+B and 5gram K2SO4 today in 180-200gal total system.

The Lamotte Potassium test kit arrived today, and i performed my first test: 09ppm Potassium. there are a number of marks on the turbidity scale, and mine clearly fell between 8 and 10.

SO, if i did have toxic levels, the water change and plant uptake accounted for the rest.

I will dose what should be 5 ppm and test again in 1 hour for comparison.
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post #8 of 42 (permalink) Old 06-06-2015, 03:19 PM Thread Starter
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I am very interested in the rate of uptake. From what you added (if I did the math right) you added only a bit over 5ppm K, and had more than that.

I definitely have something wrong - the Wisteria which had been growing like mad is stunted and strange looking tiny leaves. Some other plants (Val, Crypts) are doing very nicely. Rotala is growing nicely but leaves are small.

I've mostly stopped adding K. I think what I'll do is start with the water change amount (Equilibrium has a LOT) then a week or so later add just a bit (equivalent of 3-4ppm/week). It's the only thing I don't have tests for, and everything else looks good.

So hoping to hear how fast you find K being absorbed.

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post #9 of 42 (permalink) Old 06-06-2015, 04:15 PM
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I have some fudge numbers on actual gallons because I have 240 gallons, but I have 10 bags eco complete and quite a bit of wood. That puts my estimate at 180 actual.

I put in 1 tsp k2so4, tested an hour later and reading difference is negligible.

RO water tested at zero ppm.

I have added another Tsp, and will test end of day. I would expect to measure just over 10ppm.
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post #10 of 42 (permalink) Old 06-06-2015, 04:18 PM Thread Starter
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I've got something similar (220G with "stuff"), I wish I had taken more time to figure out displaced volume, I really don't know within 30 gallons or so how much I have.

If you are adding dry, any chance it is not quickly going into solution?

What would be interesting to know is to see it get to (say) 40ppm, then add no more and see how it decreases over time, if you are minded to do such a test.

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post #11 of 42 (permalink) Old 06-07-2015, 09:15 PM
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I'm going to get to 10ppm, then let it drop for 3 days and test.

I got a result very close to 10ppm after two tsp addition before today's 45% WC.

We shall see
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post #12 of 42 (permalink) Old 06-09-2015, 07:11 AM
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Well, i was reading the measurements incorrectly, and somehow you got your wish!

I am currently at 40ppm K on the nose.

WC was last night. i will add no K2SO4, KH2PO4 or KNO3 until next Sunday's WC and test before.

I am also at 15-20ppm NO3, and 3-4ppm PO4, so i am rating all of their drops over the week without addition.

I will be adding 1 tsp CSM+B daily to keep Iron up until i can test that, when kits arrive tomorrow.
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post #13 of 42 (permalink) Old 06-09-2015, 01:20 PM Thread Starter
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I will be adding 1 tsp CSM+B daily to keep Iron up until i can test that, when kits arrive tomorrow.
In the FWIW department, I struggled a lot with iron tests. I was using Seachem's, and my first (only 6 month old) reagent was bad, would not test a standard mix. Then I found out their instructions for chelated were for EDTA and DTPA which I was using related a lot more "cooking" before it read correctly. I would suspect other kits have some issues also, so I would recommend you mix up a solution with known concentration and also test that to calibrate your expectations.

Because of this fiasco (partly of my own making for not using a test solution) I found I was ending up at about 5-10 times the iron I was targeting for a while.

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post #14 of 42 (permalink) Old 06-09-2015, 02:00 PM
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Quote:
Originally Posted by Linwood View Post
In the FWIW department, I struggled a lot with iron tests. I was using Seachem's, and my first (only 6 month old) reagent was bad, would not test a standard mix. Then I found out their instructions for chelated were for EDTA and DTPA which I was using related a lot more "cooking" before it read correctly. I would suspect other kits have some issues also, so I would recommend you mix up a solution with known concentration and also test that to calibrate your expectations.

Because of this fiasco (partly of my own making for not using a test solution) I found I was ending up at about 5-10 times the iron I was targeting for a while.
I too have seachem's test coming. I will for sure be letting it simmer for 20 minutes before reading.
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post #15 of 42 (permalink) Old 06-09-2015, 02:37 PM Thread Starter
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I too have seachem's test coming. I will for sure be letting it simmer for 20 minutes before reading.
My suggestion is mix up a known concentration of the CSM+B, e.g. to expect 0.1 ppm iron, and test it at the same time as you test your water. Wait until it reads about 0.1 before reading your water.

I found that gluconate (e.g. Seachem Iron) takes minutes, Seachem says EDTA takes 45 minutes to read, and Seachem says DTPA takes hours (on their forums, I asked there, it is not in the instructions). I use DTPA myself and just let it sit overnight.

Also, I found that the low range test cannot be used for higher ranges, it gives wildly low readings (and they acknowledged this as well). What happens is that the deeper water column does not give enough-darker readings for higher range, so when you divide by 4 it is grossly wrong. So for a completely unknown sample either run both in parallel, or run the high range first and if there's no visible color run the low.

It does work, but it is VERY easy to get completely wrong (always low for me) readings.

Linwood

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