Are we dosing enough K? - The Planted Tank Forum
 
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post #1 of 6 (permalink) Old 12-14-2004, 06:11 PM Thread Starter
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Are we dosing enough K?

I posted this on the APD and thought it could be of interest here too.

I think that K uptake by plants might be higher than we think. I've been dosing it regularly through KNO3 and/or K2SO4 so that at water change I'm adding 20mg/l. And then mid-week adding 4-5mg/l. And I was *still* getting pinholes in the older leaves of Hygrophila corymbosa.

I've always wondered what the actual levels and uptake was so I finally broke down and bought a LaMotte K test kit (ok, so I'm a control freak!). I received it mid-week and I did the first test 3 days after water change and dosing (and before my usual mid-week dosing). The result: 8-10mg/l of K. Which logically means that I was at 0 when I did my water change!

I dosed 10mg/l of K at that point. 2 days later I measured 14-15mg/l of K in the tank. So an uptake of 4-5mg/l in two days.

Given that K is the nutrient that the majority of us never measure (we just dose to a certain level), could it be that more problems than we realize are due to a deficiency in K? and this causes an imbalance or uptake problem of other nutrients?

I'm aware of some discussions re excessive K inhibiting Ca uptake but I don't think this is an issue unless you have extemely soft water...

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post #2 of 6 (permalink) Old 12-14-2004, 06:18 PM
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thanks for the post. I was wondering the exact same thing. I will use your measurements as a guideline on dosing K.

Ray

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post #3 of 6 (permalink) Old 12-14-2004, 06:43 PM
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I have to agree with Laith. I read Tom Barr's recommendation on K dosing if you are on a regular KNO3 regimen and I've tried eliminating K2SO4 dosing, but still found those same pinholes on older leaves. Adding the K2SO4 on top of the KNO3 has eliminated the pinholes.
There may be instances where the K in KNO3 is enough, but I don't believe that I am one of those!

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post #4 of 6 (permalink) Old 12-14-2004, 07:15 PM
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Quote:
Originally Posted by GulfCoastAquarian
I have to agree with Laith. I read Tom Barr's recommendation on K dosing if you are on a regular KNO3 regimen and I've tried eliminating K2SO4 dosing, but still found those same pinholes on older leaves. Adding the K2SO4 on top of the KNO3 has eliminated the pinholes.
There may be instances where the K in KNO3 is enough, but I don't believe that I am one of those!
Same results for me. I am back to dosing K at 2x of NO3.

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post #5 of 6 (permalink) Old 12-15-2004, 10:03 AM
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Some folks were experiencing other problems and reducing K+ dosing, or eliminating it, apparently helped. I believe there were other things involved that added potassium, though- e.g., Seachem Equilibrium.

James
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post #6 of 6 (permalink) Old 12-29-2004, 08:36 PM
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Interesting, I have the exact same problem. I thought I dosed to 15-20ppm of K each week by assuming there was no K uptake, but it seems that my tank is chewing through the K like crazy. I now dose 30ppm of K and the problems went away.

What kind of potential problems am I looking at for the fishes by adding too much SO4?

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