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Discussion Starter · #1 ·
I have a relatively new (set up for almost 2 weeks) 120 gallon tank with Aquasoil. A few days ago my stems started showing signs of potassium deficiency (as expected for Aquasoil) so I've been dosing some Seachem Potassium I had on hand. However I'm a bit uneasy about the addition of so many sulfates over the long term.

I know ADA's Brighty K is some sort of potassium carbonate - is it potassium carbonate (K2CO3) or bicarbonate (KHCO3)? Presumably bicarbonate, being a weaker base, would be less likely to cause issues? Also, how much is the stated dose for Brighty K intended to raise K levels by?
 

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Children Boogie
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I'm not sure what's in Brighty K but there's nothing wrong with sulfur. Plants need quite a bit of it.

Check the online calculators. I also have brighty K in my calculator. It depends on your dosing method. I would target 10ppm for now. So that would be 66.80 mL or 55.6 pumps in your tank. Yikes. Buy a bag of dry ferts and save money.
 

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Discussion Starter · #3 ·
I'm definitely trying to stick to mixing my own. A 5 L bottle of Brighty K is $150. But one of the reasons I want to use either potassium carbonate or bicarbonate is because my water (remineralized RO) has very low KH. It'd be nice to supplement both potassium and kh at once.
 

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Discussion Starter · #5 · (Edited)
Use potassium BIcarbonate.
Duly noted. I've done some further digging and have found people have issues with K2CO3 like plant stunting or wild parameter swings. Presumably reagent grade should be pure enough?

Also I've seen anecdotes of livestock deaths when 'too much' KHCO3 is dosed - would this be due to hardness swings? The brighty K manual has warnings alluding to this, though the stated dose (~3.5 ppm) is higher than the doses some people have reported problems with (2 ppm).
 

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Children Boogie
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I think you're referring to k2co3. It's a very strong alkaline. I just remembered its used in making Chinese noodles & ramen.

KHco3 is only slightly basic. You can get food grade of these chemicals on Amazon. I have a bag of it.


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Discussion Starter · #7 ·
I ordered some off Amazon; it'll arrive tomorrow.

Using the Rotala Butterfly calculator, I've figured that ADA's stated dose of brighty K adds ~3.6 ppm K daily. Judging from some other calculations, this will add a bit more than 0.5 dKH. With daily dosing, do I have to worry about carbonate accumulation and KH rising, or is KH depleted through some mechanisms?
 

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I ordered some off Amazon; it'll arrive tomorrow.

Using the Rotala Butterfly calculator, I've figured that ADA's stated dose of brighty K adds ~3.6 ppm K daily. Judging from some other calculations, this will add a bit more than 0.5 dKH. With daily dosing, do I have to worry about carbonate accumulation and KH rising, or is KH depleted through some mechanisms?
Unless you think you have too much carbon in you tank, as in carbon dioxide in your water, the disassociated carbonates will be used just like CO2, the K part of the compound is the alkaline earth metal, it's what you're adding to keep your plants healthy, they both will be used.
 

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I have been using KHCO3 to raise the KH of some tanks. The substrate (Safe-T-Sorb) removes the carbonates, allowing the pH to drop.
Livestock are fine with changing levels of KH and pH, as long as it is done in small doses. I am just adding enough to raise the KH by about 2 German degrees of hardness.
 

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Discussion Starter · #10 ·
Unless you think you have too much carbon in you tank, as in carbon dioxide in your water, the disassociated carbonates will be used just like CO2, the K part of the compound is the alkaline earth metal, it's what you're adding to keep your plants healthy, they both will be used.
I do supplement CO2 but it's not extremely high - ~6 bps on a 120 gallon tank. I know some plants like Vallisneria can directly use bicarbonate, but wasn't sure if plants would still use carbonates in the presence of CO2. Do bacteria use carbonates at all? I know Aquasoil binds some carbonates but presumably this doesn't last forever...
 

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I have been using KHCO3 to raise the KH of some tanks. The substrate (Safe-T-Sorb) removes the carbonates, allowing the pH to drop.
Livestock are fine with changing levels of KH and pH, as long as it is done in small doses. I am just adding enough to raise the KH by about 2 German degrees of hardness.
Aquasoil also removes carbonates which might explain why ADA chooses to use potassium carbonate instead of K2SO4.
 

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I do supplement CO2 but it's not extremely high - ~6 bps on a 120 gallon tank. I know some plants like Vallisneria can directly use bicarbonate, but wasn't sure if plants would still use carbonates in the presence of CO2. Do bacteria use carbonates at all? I know Aquasoil binds some carbonates but presumably this doesn't last forever...
Plants will preferentially use CO2 over carbonates. Yes, bacteria will use carbonates as a carbon source but it's essentially not worth calculating. It's quite small.

Are you adding any other sources of potassium such as KNO3? The reason I ask is that 3.6 ppm of potassium per day is higher than EI. EI only reccomends 3.2 ppm of TOTAL K. That includes other sources such as KNO3 and KH2PO4.

As far as alkalinity for K2CO3 versus KHCO3 they are the same when targeting potassium. Bicarbonate (KHCO3) is twice as dilute as carbonate. The fact that K2CO3 has exaclty twice the amount of potassium makes the alkalinity equal for both when targeting potassium.

Here is the dose targeting ALL of the potassium for EI using KHCO3. Mind you, if your'e adding other sources you can reduce this dose.

To raise K 3.2 ppm in your 120 gallon tank you will need to add 3.72 gm of KHCO3, approximately 3 1/2 teaspoons

That dose will provide the following,

dKH 0.23 degrees
HCO3 5.0 ppm
K 3.2 ppm

That increase in KH should not really impact most tank inhabitants. Very sensitive creatures? Maybe.
 

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Discussion Starter · #13 ·
I'm not dosing KNO3 or KH2PO4 because of the new Aquasoil containing nitrogen and phosphorous. Several months down the line when the soil's more depleted with regard to these, I'll have added more livestock which will provide these nutrients to some degree, so even then I probably won't be dosing much.

What calculator are you using that has KHCO3? Rotala butterfly doesn't have it.
 

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I'm not dosing KNO3 or KH2PO4 because of the new Aquasoil containing nitrogen and phosphorous. Several months down the line when the soil's more depleted with regard to these, I'll have added more livestock which will provide these nutrients to some degree, so even then I probably won't be dosing much.

What calculator are you using that has KHCO3? Rotala butterfly doesn't have it.
I'm using mine, Zorfox's Planted Tank Calculator . It's only for Windows though. It has quite a few extras that Rotala does not have. In fact, I've added several other things I have yet to post yet. I suppose I need to get busy and do that lol.

Btw, remember the doses I gave are daily doses for EI. You will need water changes to prevent too much build up. If your'e not doing water changes then K2SO4 at a lower dose would be a better option IF your aquasoil is not reducing the KH enough.
 
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