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Old 02-15-2007, 09:57 PM   #1
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K in Mono potassium Phosphate (KH2P04)?

Is there a calculator for Potassium (K) in Mono potassium Phosphate (KH2P04)? The version of Chuck's Calc that I have does not compute it.

The more I read the more I think I may be deficient in potassium. What would the symptoms be for a K deficiency?

Would the best way to bring the K value to an exceptable EI level be to add Potassium Sulfate (K2SO4)? Would I need to be concerned about the SO4 levels?

Chuck's calc is suggesting that I would need to add 1.5 tsp of K2SO4 along with my .75 tsp KNO3 to get K to the appropriate level of 20ppm. This is not taking into account the very small amount (.4 grams) of KH2PO4 that I add 3x weekly. 1.5 tsp K2SO4 seems like quite a lot... I have been doing .25 tsp 3x weekly.
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Old 02-15-2007, 10:36 PM   #2
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I've never heard of any reason to be concerned about the Sulfate in K2SO4. It is a micro nutrient and should be more beneficial than the Chloride if you were adding KCl instead.

Nutrient Deficiencies

That dosing sounds right to me. The Potassium Sulfate is one of the ferts that I tend to go through faster.
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Old 02-16-2007, 07:39 AM   #3
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What is your tank size?
I am also there, trying to figure out the perfect dosing schedule...
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Old 02-16-2007, 08:19 AM   #4
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My tank is a 75 gallon, with high light (260w CF).

Edited to say: Thanks for the information & link Purrbox. At least now I don't think I am crazy for calculating that volume requirement . Also, does anyone know of a K hobby grade test kit?
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Old 02-16-2007, 08:49 AM   #5
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Potassium is one of those nutrients that is supposedly "impossible" to overdose. No test kit really required, especially if you are using EI. I dose it every other day with my Nitrates and Phosphates.

The amount of Potassium in Potassium Phosphate is very low. If the only Potassium going into your tank is from KH2PO4, then you're hardly getting any at all (less than 0.5 ppm K for every ppm PO4 you dose).

Those number aren't exact, but you get the picture.
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Old 02-16-2007, 01:29 PM   #6
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I wouldn't worry about testing for K. Like JRagg said, it is almost impossible to overdose potassium. A little extra is not going to hurt anything, and is better (in the K case) than too little.
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Old 02-16-2007, 01:29 PM   #7
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Dr. Prescott at the now defunct Aquarium Landscapes used to sell a K turbidity test kit that I tried out. It was only designed to detect levels of K above 1 ppm (basically it got cloudy if your K was above 1 ppm, otherwise it was fairly clear. This doesn't do much good when you're trying to maintain levels in the 10-20 ppm range. My best advice is to dose a total of 20 ppm of K every week, rather than trying to maintain a certain level. This is the way I dose it and my plants seem to like it
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Old 02-16-2007, 05:03 PM   #8
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This spreadsheet will calculate the K in KH2P04.

http://webpages.charter.net/zezmo/EI..._v4_public.xls
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Old 02-16-2007, 05:33 PM   #9
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Very nice Zezmo I would note that the amount of K in Mono-Potassium Phosphate is virtually inconsequential unless you are completely anal about it like Zezmo and I :P Great tool
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Old 02-16-2007, 09:43 PM   #10
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I've heard bad things about high phosphate levels. Considering K2S04 is 55.1% sulfate(which i guess is a phosphate?) would that not put the phosphates into a toxic level?

I stopped dosing K2S04 about 2 months ago while fighting a green water problem and high phosphates in tap water putting it over 20ppm with dosing. I have seen no ill effects yet.

If anyone is a member on aquaria central there is a sticky from Tom Barr about using KN03 as the sole source of K as long as you don't have high N03 levels out of the tap.

Here's a link http://www.aquariacentral.com/forums...ad.php?t=21033
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Old 02-16-2007, 10:47 PM   #11
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Phosphate and Sulfate are completely different chemicals. No way you could high levels of Phosphate from dosing K2SO4.

You are correct that if you are dosing enough KNO3 there is no need for the separate Potassium dosing. As someone with Nitrates in my tap, it's not an option for me.
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Old 02-17-2007, 12:13 AM   #12
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The highest phosphate levels that I have ever tested in my tank is somewhere between 1 & 2 PPM. I was initially dosing too much, with a gross bloom of algae. But now that I know what I am dosing and what comes in my tap water, my phophate levels are in the appropriate range. I was originally trying to figure out the volume of potassium in the KH2PO4 that I was dosing.

In terms of volume, I am thinking of using NPK ratios of 9-1-18:

9.375 - 1 - 18.75
(KNO3) - (KH2PO4) - (K2SO4)
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Old 02-17-2007, 01:03 AM   #13
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Thanks Travis for the kind words about my spreadsheet. I find it an invaluable tool for tweaking my fert routines on various tanks.

Just a note on supposed phosphate issues. I accidentally got two of my fert containers mixed up over that last couple weeks. I thought I was dosing K2SO4, but was in fact dosing KH2PO4. For 3 weeks I have been adding 1tsp of KH2PO4 at water change, and 3 tsp of 10% fleet during the week (18.03 ppm of P). This week I decided to crank up what I thought was the Potassium. Instead I accidentally cranked up the phosphate.
On Sunday after my water change, I added 2.5 tsp of KH2PO4, and 1 tsp of 10% fleet to my 72g. Thats 37.08 ppm of phosphate.
End result? nothing. Fish are fine, cherry shrimps are fine...plants...fine.... algae...no issues. In fact everything is pearling like mad as I write this. One minor effect is that the red in the E. tennelus "red" has really come on strong. Now, I did not add more phosphate on macro days this week, and I have been adding extra KNO3 and K2SO4 to help encourage the plants to uptake some of that P. Oh, and of course a valuable lesson on labeling your chems, instead of "I will just remember what this is".
None of this was intentional, but, it has further enhanced my belief that phosphate is not the villain it is often made out to be.
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Old 02-17-2007, 06:02 AM   #14
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Niiiiiiiiiiiiiiiice!

You have just proved a very good point Zez.

PO4 is not the culprit everyone would like it to be. In my opinion N is almost always what gets you. Whether too much or too little. Nice work my man
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Old 02-17-2007, 12:45 PM   #15
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That's some great information. Thanks everybody. Maybe I should start dosing KH2PO4 again to try to get some more color out if my Ludwigia Repens.

Strange that my phosphate levels went down when I stopped dosing though. I am slowy earning a distaste for flake food though wonder if that might be the culprit. Guess it doesn't matter they are down now anyway.
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