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Is Sulphate of Potash safe to use in aquariums?

Akmaliano

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dw1305

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Hi all,
Sulphate of Potash safe to use in aquariums in place of Potassium Sulphate
They are the same compound, K2SO4.

For historical reasons agricultural fertilisers have to state their potassium (and phosphorus compounds) as oxides, rather than elements. So "potash" is potassium oxide (K2O).

You can work out the percentage potassium (K) using the <"Periodic Table">, and the <"RAM"> of the elements, to give you the <"RMM"> of the compound.

Potassium has a RAM of 39.1, oxygen (O) = 16 and sulphur (S) = 32.1.

Potash K2O is (39.1*2) + 16 = 78.2 + 16 = 94.2 so the RMM is 94.2 and the percentage K is 78.2/94.2 = 0.83 = 83% K. When you've add 10 grams of K2O you've added 8.3g of potassium.

You can do the same for K2SO4: ~ 78.2 + 32.1 + (4*16) = 110.3 + 64 = 174.3 and the percentage K is 78.2/174.3 = 0.45 = 45% K. When you've add 10 grams of K2SO4 you've added 4.5g of potassium.

cheers Darrel
 

Akmaliano

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Thanks Darrel. As always, a very comprehensive explanation :thumbup:
so it's okay to use those horticultural grade "sulphate of potash" products to boost potassium in an aquarium then?
 

dw1305

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Hi all,
so it's okay to use those horticultural grade "sulphate of potash" products to boost potassium in an aquarium then?
Yes, they will be of very slightly lower purity than the soluble fertilisers, or food grades, of the same compound, but it makes absolutely no difference in use.

Nearly all potassium compounds are soluble, so it will go straight into solution as K+ ions (and SO4--) ions.

cheers Darrel
 

Akmaliano

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Hi all,Yes, they will be of very slightly lower purity than the soluble fertilisers, or food grades, of the same compound, but it makes absolutely no difference in use.

Nearly all potassium compounds are soluble, so it will go straight into solution as K+ ions (and SO4--) ions.

cheers Darrel

Excellent, thanks Darrel
 

Akmaliano

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Hi Darrel - one more question. Which days should I be dosing the potash? With Macros or Micros?
Also, which days to dose Magnesium (Epsom salts)?

Many thanks
ak
 

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Dose both potassium sulphate and magnesium sulphate on the alternate days to the micros, as these salts are macro salts.

What are you using to supply nitrate, if not dosing potassium nitrate ?
 

Akmaliano

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Dose both potassium sulphate and magnesium sulphate on the alternate days to the micros, as these salts are macro salts.

What are you using to supply nitrate, if not dosing potassium nitrate ?

Thanks Ian. I am dosing potassium nitrate via the ususal Macro solution but have been adding more potassium lately.
Is it better to divide the dose of potassium sulphate and magnesium sulphate across 3 days or can I just add the whole lot post-water change?

many thanks
 

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Better to add small doses alternate daily, as the macro will react with the micro neutralising the effects of them both.

Are you sure you are adding sufficient nitrate, if only dosing smaller (?) doses of potassium nitrate ?

I have never heard of anyone ever really having potassium deficiency, but much more common is nitrate deficiency.
 

Akmaliano

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Are you sure you are adding sufficient nitrate, if only dosing smaller (?) doses of potassium nitrate ?.

I'm dosing KNO3 as per APF's guidance, and even slightly more: 9-10tsp per 1000ml water (APF says 4tsp per 500ml). Do I still need to add extra nitrate then?
 

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Do I still need to add extra nitrate then?
Not really. Why are you dosing potassium sulphate then ?

APF's guidance is a fine start. Dose more if you have a large plant mass, dose less if less plants.
 

Akmaliano

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Not really. Why are you dosing potassium sulphate then ?
I was getting pinholes on lower leaves especially on the Ludwigia Repens and thought I should dose more K which I'm adding as potassium sulphate dry salt
 

ian_m

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I was getting pinholes on lower leaves especially on the Ludwigia Repens and thought I should dose more K which I'm adding as potassium sulphate dry salt
As you are dosing EI I doubt it is potassium deficiency.

Most plant "mechanical issues" are either fish nibbling or poor CO2. How big is your tank, how big is your filter etc.

Though dosing potassium sulphate should do no harm.
 

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I'm running a Roma 240. I have considered the flow but with an FX4 + Fluval 306 + Hydor 3200 I have been inclined to discount that factor especially given that I can notice pretty good (at times quite strong) swaying of plants.

I know that I have Mg issues which in turn have led to Iron issues. I'm attaching a pic of how my ludwigia looked like a couple of weeks ago.
 

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ian_m

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I'm attaching a pic of how my ludwigia looked like a couple of weeks ago.
Obvious from pics, too much light for CO2 levels. Simple. Easy fix, sort CO2 levels or lower light levels.

If dosing EI correctly (with weekly water changes) you will not have nutrient deficiency issues, therefore must be CO2 levels or the light levels supplied. Job done.
 

Akmaliano

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Thanks for your feedback Ian. My drop checker is bright green/almost yellow, so I guess I need to turn down the lights a bit.

Which is more important for light: intensity or duration?
 

ian_m

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Light intensity probably.

Try putting the drop checker amongst the plants that are having issues and see what it says.

A pH profile using a meter is also handy in that a drop of 1pH from CO2 on till lights on as about 30ppm CO2.
 

Akmaliano

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My DC is in opposite corner to the outtake of the 306 from which co2 come out, and about 5 inches above substrate.
The hydor powerhead is next to the 306 outtake pushing the water well into the centre of the tank.
Overall I'm pretty sure that the co2 is sufficient and being moved around.
The lights come on as follows:
- roma 240's stock light (not very powerful) 13.30-21.30
- fresh & plant 2.0 59w at 100% intensity 14.00-20.45
Is this too much light?
 
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