Potassium test kits and dosing levels? - The Planted Tank Forum
  • 2 Post By kevmo911
  • 2 Post By Virc003
  • 2 Post By Little Soprano
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post #1 of 7 (permalink) Old 01-03-2016, 07:52 AM Thread Starter
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Potassium test kits and dosing levels?

I'm curious to see what my potassium levels are in this tank, but the only kit I can find is the Red Sea one. Even though this is marketed as a SW kit will it work for FW? I've used the calcium API test on my FW tank with no problem, and since this is a titration kit as well will it still be accurate?

Also I did a little math, and my dosing & livestock puts my nitrates at 30ppm (tested is right), phosphates at a little under 5ppm (tad high but stems haven't started growing OK with this number, tested also at around 5ppm), and with some math and the old petalphile calc, I am getting only 11.57ppm of potassium.

What is the right ratio for this? This is copied from the barre report:
EI target ranges from this forum for high-light CO2 injected tanks-

CO2 range 25-35 ppm
NO3 range 10-30 ppm
K+ range 10-30 ppm
PO4 range 1.0-2.0 ppm
Fe 0.2-0.5ppm or higher
GH range 1-2 degrees "extra" 17-40 ppm or higher

So if I were to aim for the 10-30 ppm range for potassium, which fertilizer would you dose more of? K2SO4 right? Is there any harm in adding more with the added SO4?

My anubias are showing potassium deficiency-pinholes on the older plants' old growth.

Added this is my annual water report; it's actually pretty nice tap water for plants-pH is a consistent 7.6:

Last edited by Little Soprano; 01-03-2016 at 08:11 AM. Reason: added
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post #2 of 7 (permalink) Old 01-04-2016, 04:11 AM
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I would also like to know if there is a freshwater potassium test kit.
I have been searching, but a little skeptical on what to buy.
I hope someone has some good information we can use
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post #3 of 7 (permalink) Old 01-08-2016, 03:03 AM
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Does anyone have an idea on testing potassium?
Thank you
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post #4 of 7 (permalink) Old 01-08-2016, 03:20 AM
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With potassium, as with nitrates and phosphates, you'd have to try really, really hard to add enough to do any damage to your plants or fish. Macros aren't an issue. It's perfectly safe to dose standard EI doses and beyond. If you think you may have an issue with potassium deficiency, you can generally increase all macros with no danger. If it doesn't do the trick, you have another issue, and you can drop macro dosing back down to standard levels after a couple weeks. That said, if you want to increase potassium specifically, you can add K2SO4 to the mix of KNO3 and KH2PO4, without reducing the application of the other two. Again, however, drop it back down to normal if there's no positive results within a couple weeks.

The only current argument regarding overdosing EI involves micros, which is a whole different story.

Just make sure that if you're doing EI dosing, you're including the 50% water changes weekly. If you're not doing that, you're not using EI dosing.

But, I've never used a potassium test kit, and I'm not sure API (which is the most common brand of test kits we use) makes one.
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post #5 of 7 (permalink) Old 01-08-2016, 04:02 AM
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If I remember correctly, I looked into this sometime in the kast year and found freshwater and saltwater tests will give different results. Furthermore freshwater K tests ended up being too expensive. The 'cheap' kits I found were above $100 for a hand full of tests. For kits with any reliability the price was $300+ for the same number of tests.

I want to say my source came from a barreport thread but I honestly can't say for sure.
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post #6 of 7 (permalink) Old 01-08-2016, 06:14 PM
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Thanks for the answers.
I guess the perfectionist in me wants to be as spot on with my dosing as possible
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post #7 of 7 (permalink) Old 01-11-2016, 05:42 PM Thread Starter
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Well I know they make SW, but they are actually reasonably priced. Its a shame they are so expensive for FW.

Right now in my 120 I'm dosing:
1-1/2 tsp of KNO3
1/2 tsp of KH2PO4
1 tsp of K2SO4-was dosing 1/2 tsp per EI recommendations

The s. repens seems to be a potassium hog by the looks of it. It's leaves are starting to get darker again and my pinholes aren't showing up anymore, but the s.repens looks like it wants MORE. Which is crazy, but I figure I'll give it another week or two (to get my CO2 up to proper levels), and then mess with levels again.

I do do a 50% W.C. per week.

I do a very reduced micro dosage however. Tuesday and Saturday are 1/2 tsp of plantex, Thursday is 14ml of Seachem Aquavitro Iron, no other micros. So Plantex is only twice a week vs 3.

I've also been dosing at night instead, so I can't forget. I do it when I get home from work (work 4-2:30am), so about 3:30 am. So Monday's dose is done on Sunday night, Tuesday on Monday, etc.
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Last edited by Little Soprano; 01-11-2016 at 06:18 PM. Reason: added
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