Potassium sulfate and EI dosing - The Planted Tank Forum
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post #1 of 5 (permalink) Old 12-17-2018, 10:04 AM Thread Starter
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Potassium sulfate and EI dosing

Greetings Everyone,

I'm going to be starting my first planted tank in the next few weeks, and one of the things I'm trying to figure out is the fertilizer. I spent many years successfully keeping reef aquaria, and the whole idea of adding nutrients to the water is a bit crazy to me.

I have decided to go with the EI dosing strategy. I prefer to dose using pre-made liquid solutions, so I did some searching online and I found the EI calculator at www.aquariumcalculators.com. This is a great calculator, but it seems to ignore potassium sulfate for the macro nutrient solution. In the comments section, Nigel (perhaps the creator of the calculator?) states that potassium sulfate is not needed.

If potassium sulfate is not needed, then why is it included in all of the EI packages for sale? Assuming it is needed, does anyone know the weight ratio between potassium sulfate and the other components of the macro solution are? For example, if my formula indicates 74 g of potassium nitrate and 20 g of mono potassium phosphate, how much potassium sulfate should I add?

Thanks everyone in advance for your help.

Cheers
TMQ
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post #2 of 5 (permalink) Old 12-17-2018, 02:00 PM
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Check these out. Dosing Instructions


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post #3 of 5 (permalink) Old 12-17-2018, 02:38 PM
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I really like the Rotala Butterfly calculator myself - https://rotalabutterfly.com/nutrient-calculator.php . It will calculate just about any compound you might use, as well as most brand name pre made solutions. And in addition to EI, you can calculate the result of a dose, or dose to target ppm. That is very useful. It also has an option for creating your own solutions. So if you ever decide you want to try making your own to save money, it makes that easy as well.


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post #4 of 5 (permalink) Old 12-17-2018, 05:20 PM
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Quote:
Originally Posted by Mighty Quinn View Post
Greetings Everyone,

I'm going to be starting my first planted tank in the next few weeks, and one of the things I'm trying to figure out is the fertilizer. I spent many years successfully keeping reef aquaria, and the whole idea of adding nutrients to the water is a bit crazy to me.

I have decided to go with the EI dosing strategy. I prefer to dose using pre-made liquid solutions, so I did some searching online and I found the EI calculator at www.aquariumcalculators.com. This is a great calculator, but it seems to ignore potassium sulfate for the macro nutrient solution. In the comments section, Nigel (perhaps the creator of the calculator?) states that potassium sulfate is not needed.

If potassium sulfate is not needed, then why is it included in all of the EI packages for sale? Assuming it is needed, does anyone know the weight ratio between potassium sulfate and the other components of the macro solution are? For example, if my formula indicates 74 g of potassium nitrate and 20 g of mono potassium phosphate, how much potassium sulfate should I add?

Thanks everyone in advance for your help.

Cheers
TMQ
Hi @Mighty Quinn,

I agree it is confusing, some EI kits include potassium sulfate while some don't. I think it comes down to two things, first is my local water - does it contain a lot of potassium. In my case it does not. Secondly am I dosing my KNO3 at the full recommended amount (i.e. 7.5 ppm)? In some tanks I do dose the full amount of KNO3 which means I am dosing about 4.73 ppm of potassium or a 1.5:1 ratio which is a suggested ratio. I also dose mono potassium phosphate (KH2PO4) which at the recommended EI dosing rate adds an additional 0.54 ppm of potassium. So if I am dosing EI per the recommended doses in theory I should have more than sufficient potassium.

However some of my tanks have more fish and require less KNO3 to maintain a 20 ppm - 30 ppm of nitrate level. In those tanks I may dose one half (1/2) the recommended amount of KNO3 or less. In some cases there may be sufficient potassium in the local water supply to offset the potassium reduction - that is not the case here in Seattle where my local water has about 2 ppm of potassium. So, when I reduce the amount of KNO3 I dose to maintain a moderate level of nitrates I have to add potassium sulfate (K2SO4) to offset the difference.

How do I know? In a tank with a moderate bioload (aka fish) I was dosing about 1/3 the recommended EI dose of KNO3. I thought I was offsetting the decreased potassium with the amount of K2SO4 I was dosing however I was not. The stem plants pretty much stopped growing, the cryptocorynes started melting and dieing back, the plants did not have the vibrant green that they had in the past. I found recently that I was drastically under-dosing my potassium. I increased my potassium and the stem plants started growing again and the cryptocorynes started putting out new leaves. What tipped me off? The white flecks (necrotic area) on some of the older leaves of my Nymphaea micrantha.

N. micrantha (Tri-color Lotus) showing white flecking characteristic of potassium (K) deficiency
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post #5 of 5 (permalink) Old 12-18-2018, 02:17 AM Thread Starter
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Thank you everyone for your responses! They were tremendously helpful!

Just to bottom line things, I think what you all have essentially said is if you are using KNO3 and KH2PO4 to maintain your nitrate and phosphate levels per the EI method, then your potassium levels are probably just fine. The exception to this when you have a heavy bioload or other source of nitrates and/or phosphates, hence you need to back off of the KNO3 and KH2PO4 so you don't overload your tank with nitrates and/or phosphates, and therefore you need another source of potassium. Does that sum it up?

Is it correct to assume that if I include the "optional" K2SO4 into macronutrient liquid (per the link that Maryland Guppy provided) that the extra potassium and sulfate are not going to harm anything?

Thanks again!
Cheers,
TMQ
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