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post #1 of 7 (permalink) Old 05-02-2015, 12:55 PM Thread Starter
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kno3 kh2po4

in general if nitrates are high and reduce suggested EI kno3 fert by half do I need to increase recommended kh2o4 to compensate for potassium lost at kno3? thanks,
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post #2 of 7 (permalink) Old 05-02-2015, 12:57 PM
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post #3 of 7 (permalink) Old 05-02-2015, 01:15 PM
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You was potassium sulfate not phosphate. K2S04
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post #4 of 7 (permalink) Old 05-02-2015, 02:16 PM
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Using my 10g as an example...
1/8 tsp KNO3 is recommended minus half = 1/16 tsp.
1/64 tsp of KH2PO4 is recommended.
If you wanted to get the other 1/16 tsp of KNO3 that you lost you likely would
need to up the KH2PO4 at least to 1/16 tsp.
This would be way over the recommended amount of it.
Since it is where the Phosphates come from, you don't want that.
The K2SO4 adds something that is needed and not in the KNO3 anyway.
It would be the normal substitute for KNO3.
In fact, look on here...
https://www.plantedtank.net/forums/sh...ad.php?t=21944
and see that it is added as an "optional" on the list of nutrients.
In my tank since I don't have much plants, if I do use the 1/8 tsp
that is recommended it gives me a red test result on Nitrates
when tested just before water change. So the plants haven't use
enough of it. So if I dose 1/32 tsp of KNO3 and 1/32+1/16 tsp of K2SO4
then the test just before the water change in light Orange or about 10-15 ppm
on the nitrates. That way I'm getting my full 1/8 tsp for the total.

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post #5 of 7 (permalink) Old 05-02-2015, 03:01 PM
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Quote:
Originally Posted by bsantucci View Post
You was potassium sulfate not phosphate. K2S04
In addition to the potassium sulfate I'm recommending also potassium bicarbonate - KHCO3 .

Last edited by Silver R.; 05-02-2015 at 03:02 PM. Reason: 1x typo
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post #6 of 7 (permalink) Old 05-02-2015, 03:13 PM
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Quote:
Originally Posted by bsantucci View Post
You was potassium sulfate not phosphate. K2S04
Good catch.
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post #7 of 7 (permalink) Old 05-02-2015, 03:36 PM
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Ditto:
Use K2SO4 to supply the extra potassium needed.

Potassium bicarbonate is used in small amounts if you need to raise the carbonates. While it does supply potassium, it will also raise the KH. When you use enough to raise the potassium by 14 ppm this also raises the carbonates by 1 German degree of hardness. This may be just fine in a hard water tank (increasing the KH by 1-2 degrees though the week is not a lot of change in a hard water tank), but if you keep on doing this to supply the plants with potassium, the KH is going to keep on rising until you do a water change. This will almost always raise the pH too high in a soft water tank. To correct the KH back down for a soft water tank you would use water that is lower KH than the tank, and this might cause a shift in parameters greater than the fish can handle.

KH2PO4 also has potassium, but is dosed in small amounts to supply the right amount of phosphate. If you dosed enough to supply the needed potassium you would be WAY overdosing the phosphate. You use so little KH2PO4 to supply the right level of phosphate that the potassium pretty much does not count.
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