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K2CO3 (Potassium carbonate) Dosing

noodlesuk

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21 Jul 2020
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322
Location
Oxfordshire
From help on here and looking at deficiency charts, it looks like there is a Potassium deficiency in my tank (black edged leaves and holes). I purchased some dry salts (50g of K2CO3) and as per instructions, mixed with 500ml of water. The instructions that came with the salts suggest 1mL of solution per 100L.

I have a 20L low tech, heavily planted, which I currently dose 1mL per day of TNC complete and 1mL of Liquid Carbon. I do a 50% water change each week. So would it be best add 0.2mL (of K2CO3 solution) each week after the water change?

I tried the calculator for K2CO3, but wasn't sure what to select for "I AM CALCULATING FOR". I tried a few options, but it showed 0 for most of them, so must be doing something wrong! Thanks for any help.
 
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Bear in mind that K₂CO₃ will also increase your KH, and hence also pH. Depending on the fauna in your tank, you may need to proceed slowly.

You are currently dosing the “triple” dose of TNC Complete, as recommended by the manufacturer as an approximation of EI. However, that dose is fairly mild, and doesn’t give you a particularly rich form of EI.

It is often suggested (and I’ve done this successfully myself) that you can further double that dose (a “double-triple” dose), and this gives you a “full-fat” EI dose. I would recommend you do this rather than using K₂CO₃ which has the side-effect of changing KH and pH. There’s no way you’d get any deficiencies with the “double-triple” dose of TNC Complete.

The “double-triple” dose would get quite expensive on a larger tank, but for a 20 litre it’s fine. Of course you could switch to DIY salts (as I have), which gives you total control. You’d want potassium nitrate KNO₃, monopotassium phosphate KH₂PO₄, and potassium sulphate K₂SO₄. None of these will affect KH, and will not have an appreciable effect on pH.
 

noodlesuk

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21 Jul 2020
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322
Location
Oxfordshire
Bear in mind that K₂CO₃ will also increase your KH, and hence also pH. Depending on the fauna in your tank, you may need to proceed slowly.

You are currently dosing the “triple” dose of TNC Complete, as recommended by the manufacturer as an approximation of EI. However, that dose is fairly mild, and doesn’t give you a particularly rich form of EI.

It is often suggested (and I’ve done this successfully myself) that you can further double that dose (a “double-triple” dose), and this gives you a “full-fat” EI dose. I would recommend you do this rather than using K₂CO₃ which has the side-effect of changing KH and pH. There’s no way you’d get any deficiencies with the “double-triple” dose of TNC Complete.

The “double-triple” dose would get quite expensive on a larger tank, but for a 20 litre it’s fine. Of course you could switch to DIY salts (as I have), which gives you total control. You’d want potassium nitrate KNO₃, monopotassium phosphate KH₂PO₄, and potassium sulphate K₂SO₄. None of these will affect KH, and will not have an appreciable effect on pH.
Thanks for the very informative reply. I hadn't appreciated the knock on effect with KH and pH, but now makes sense. I'll try increasing the TNC dose to 2mL, to get the extra nutrients. Many thanks for your help.
 

dw1305

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7 Apr 2008
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nr Bath
Hi all,
I purchased some dry salts (50g of K2CO3) and as per instructions, mixed with 500ml of water. The instructions that came with the salts suggest 1mL of solution per 100L.
You need to work out how much potassium (K) (mg/L) is in 1mL of your stock solution first. Your compound is 55.77% potassium, which means that 50g contains 27.89g of potassium.

I'm going to assume you made the solution up to 500mL (weight water + K2CO3)? for the moment. If you added 50g to 500 mL? You need to use 550 as your volume.

The unit "mg/L" is the same as "ppm" and you had 27.89g in 500 mL, which is 55.77g in 1000 mL.

A thousand mL is one litre, and there are a thousand milligrams in a gram, so now we 55.77 x 1000 = 55770 and your (500g in 500mL) stock solution is 55770 ppm.

If we dose that stock solution at 1mL in 100 litre we have to go all through the powers of 10 in the opposite direction. Now we have 1mL which is a gram, and there are 1000 gram in a litre so we divide 55770 by 1000 to get back to 55.8 ppm and then we divide that by 100 (volume in litres of the tank) to give us 0.56 ppm.

So not a huge potassium (or dKH) addition. If you dosed that 1 mL in 20 litres that is (0.55 * 5) ~ 2.79 ppm K and if you dosed 5 mL in 20 litres that would be (2.79 * 5) ~ 14 ppm K.

cheers Darrel
 

Wookii

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13 Nov 2019
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2,087
Location
Nottingham
I think most people looking to add Potassium for EI purposes will use Potassium Sulphate - K2SO4, since it won’t affect alkalinity and pH like Potassium Carbonate (K2CO3) will.

Edit: Sorry, I see @Dr Mike Oxgreen has already covered that - shouldn’t skim read lol
 
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