Need help with potassium fertilizers - The Planted Tank Forum
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post #1 of 10 (permalink) Old 07-29-2020, 04:55 PM Thread Starter
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Need help with potassium fertilizers

My tank is a Walstad tank and even though I feed my fish more than enough, a potassium deficiency always seem to pop to some extent. Aside from that, everything is well.

What I would like to know is how can I occasionally dose my tank with potassium without having to add phosphates, nitrates, etc.? My nitrates always stay in the 5-10ppm and phosphates at 1ppm. I know there is potassium sulfate but in Diana's book, it says that too much sulfate can cause H2S to form in the substrate and I'm not having much luck with finding potassium chloride.

Any suggestions?

Edit: mods, can you please move this to the correct subforum?

Last edited by MintyFresh; 07-29-2020 at 04:58 PM. Reason: Wrong forum
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post #2 of 10 (permalink) Old 07-29-2020, 05:49 PM
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Potassium chloride is sold as "muriate of potash" and you can probably find it in your grocery store as a salt substitute like "No Salt" (but keep an eye out for other ingredients that might be included).
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post #3 of 10 (permalink) Old 07-30-2020, 02:55 PM Thread Starter
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Potassium chloride is sold as "muriate of potash" and you can probably find it in your grocery store as a salt substitute like "No Salt" (but keep an eye out for other ingredients that might be included).
Thanks. I'll check those out. I know that this type of potassium can be bought for water softeners but I don't need a 40lb bag of it for one aquarium. Lol
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post #4 of 10 (permalink) Old 07-30-2020, 03:36 PM
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Garden centers and hardware stores also sell Muriate of Potash. I saw a 4-pound bag for $15.95.
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post #5 of 10 (permalink) Old 07-30-2020, 07:15 PM Thread Starter
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Garden centers and hardware stores also sell Muriate of Potash. I saw a 4-pound bag for $15.95.
I never thought to check garden centers. Thanks!
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post #6 of 10 (permalink) Old 07-30-2020, 10:30 PM
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Make it easy on yourself and buy a product designed for aquarium use, unless you want to get into measuring powder and determining dosing (which isn't all that difficult). Products such as SEachem Potassium or API's Leaf Zone (which also adds iron) are much simpler. You might also consider some AIO packages such as NilocG's products.

If you want to go the powder route, then buy K2SO4 (potassium sulfate). All of these products are available on the likes of Amazon and many are in your LFS.
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post #7 of 10 (permalink) Old 07-30-2020, 11:24 PM Thread Starter
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Make it easy on yourself and buy a product designed for aquarium use, unless you want to get into measuring powder and determining dosing (which isn't all that difficult). Products such as SEachem Potassium or API's Leaf Zone (which also adds iron) are much simpler. You might also consider some AIO packages such as NilocG's products.

If you want to go the powder route, then buy K2SO4 (potassium sulfate). All of these products are available on the likes of Amazon and many are in your LFS.
I have API Leaf Zone but the potassium is derived from potassium sulfate. The reason I want to try to avoid sulfate is because of what I said in my OP:

Quote:
I know there is potassium sulfate but in Diana's book, it says that too much sulfate can cause H2S to form in the substrate
My substrate is organic so I don't want to take the chance of adding too much sulfate.
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post #8 of 10 (permalink) Old 07-31-2020, 12:33 AM
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I have API Leaf Zone but the potassium is derived from potassium sulfate. The reason I want to try to avoid sulfate is because of what I said in my OP:



My substrate is organic so I don't want to take the chance of adding too much sulfate.
You won't have a problem with sulfate. The little bit of sulfate (< half the potassium) won't cause such issues and plants need the sulfate in decent quantities as well. I'd be more concerned about the accumulating chloride, but not too concerned even with that. You just don't need that much potassium in a low-tech setup.
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post #9 of 10 (permalink) Old 07-31-2020, 01:28 AM Thread Starter
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You won't have a problem with sulfate. The little bit of sulfate (< half the potassium) won't cause such issues and plants need the sulfate in decent quantities as well. I'd be more concerned about the accumulating chloride, but not too concerned even with that. You just don't need that much potassium in a low-tech setup.
Interesting. I've always heard about the negatives of adding too much sulfate to walstad tanks but not chloride. What can happen if there is too much chloride in a tank?

How often do you think it would be best to add potassium? I was thinking about twice a month for now and then to just one a month because I don't want to get into the whole weekly dosing that some people do.
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post #10 of 10 (permalink) Old 07-31-2020, 04:00 AM
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Interesting. I've always heard about the negatives of adding too much sulfate to walstad tanks but not chloride. What can happen if there is too much chloride in a tank?

How often do you think it would be best to add potassium? I was thinking about twice a month for now and then to just one a month because I don't want to get into the whole weekly dosing that some people do.
Chloride can become toxic to plants, although there is disagreement on how much. My opinion is that, much above 7ppm and trouble will develop. However, as I mentioned, you will be adding so little potassium that neither chloride nor sulfate will be a concern. I suggest maintaining a minimum 2-3ppm K. In a high-tech tank, we'd lean more toward maintaining, at least, an equal amount of K to calcium. If you add K2SO4 or KCl, you get the same amount of SO4 as you do KCl, for the same amount of K, but plants use up SO4 much faster than they do chloride. So, both will build up week after week depending upon how much water you change when you do water changes and there will always be more chloride than if you dose with sulfate.

It is about maintaining some minimum level of K. Although plants won't consume it rapidly, they seem to like have a lot of it around. So, your water changes should guide you, e.g.; if you add 3ppm and you do a 50% water change, you'll want to add 1.5ppm after the water change. There are other factors, such as accumulation and uptake issues, but that is a basically good way to look at when and how much.
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