Optimum Ca:Mg:K Ratio - Fertilizing - Aquatic Plant Central

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Unread 02-27-2020, 11:36 AM   #1 (permalink)
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Default Optimum Ca:Mg:K Ratio

Hi Folks,

I'm new around here so if this question has been posed before, please point me to the relevant thread(s).

What do you consider to be the optimum Ca:Mg:K ratio (in the water column) for planted tanks? Having been reading around, it seems that 3:1:0.5 is preferred by some people.

I am aware that kekon did a lot of experimentation on this.

Any feedback would be greatly appreciated.

Thanks in advance.

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Unread 02-29-2020, 08:33 AM   #2 (permalink)
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Default Re: Optimum Ca:Mg:K Ratio

I don't think there is an optimum ratio of any of the nutrients. We need to meet the plants' needs for each nutrient, and having more than they need does not harm the plants. Having a lot more of a nutrient that the plants need can cause algae problems. But, ratios don't seem to fit into this.
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Unread 03-02-2020, 05:33 AM   #3 (permalink)
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Default Re: Optimum Ca:Mg:K Ratio

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Originally Posted by hoppycalif View Post
I don't think there is an optimum ratio of any of the nutrients. We need to meet the plants' needs for each nutrient, and having more than they need does not harm the plants. Having a lot more of a nutrient that the plants need can cause algae problems. But, ratios don't seem to fit into this.
Hi Hoppy,

Thanks for your reply, which is very helpful.

I asked this question because some people seem to think that there is an optimum ratio as I said in my original post. If that's not the case, can you please advise the nutrient requirements for, say, plants that grow in Amazonian waters? I am aware that the many rivers and tributaries of the Amazon includes everything from clearwater to blackwater.

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Unread 03-02-2020, 07:25 AM   #4 (permalink)
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Default Re: Optimum Ca:Mg:K Ratio

No, I can't tell you that, and I doubt that anyone can. Plants have different nutrient needs. If they have a good root system, and spend part of the year as marsh plants, they will have different needs from floating plants, for example. If we really want the optimum amount of nutrients in the water we need to determine that ourselves for the plants we have and the light intensity we have. One way to do that is to increase our dosage of just one nutrient, then observe the plants to see if they do better. Repeat this until the increase doesn't improve them. Then repeat for each nutrient.
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Unread 03-06-2020, 08:57 AM   #5 (permalink)
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Default Re: Optimum Ca:Mg:K Ratio

Potassium concentration should not be lower than those of magnesium. Typically potassium should be higher than magnesium but it is difficult to estimate exact ratio. It seems K:Mg 2:1 works well.
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Unread 03-06-2020, 01:37 PM   #6 (permalink)
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Default Re: Optimum Ca:Mg:K Ratio

Gerloff (1975) determined the critical concentration of nutrients, which is sort of related to what HoppyCalif is referring to. Experiments were done with Elodea occidentalis and water alone was the source of nutrients. Results are shown in my book Table VII-2 (p. 105). Critical concentration (milligrams of element/kg dry plant wt) for K and Mg is 8,000 and 1,000, respectively. What this means is that when E. occidentalis contained less than 8,000 ppm K, it was K deficient. When it contained less than 1,000 ppm Mg, it was Mg deficient,

I would take from this, plus knowing that K is a MAJOR plant nutrient that, yes, aquatic plants need quite a bit more K than Mg. How much more? You are all welcome to pick a number!

We can all thank Gerloff for doing this bruising set of experiments!
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Unread 03-07-2020, 10:16 AM   #7 (permalink)
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Default Re: Optimum Ca:Mg:K Ratio

It also depends on sodium concentration. The more sodium the more potassium has to be dosed. Tap water usually contains 5..50 ppm of sodium. That's why some people add much more potassium with no adverse effects whilst others see some adverse effects like pale looking plants and deformed tips.
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Unread 03-14-2020, 02:33 PM   #8 (permalink)
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Default Re: Optimum Ca:Mg:K Ratio

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Originally Posted by dwalstad View Post
Gerloff (1975) determined the critical concentration of nutrients, which is sort of related to what HoppyCalif is referring to. Experiments were done with Elodea occidentalis and water alone was the source of nutrients. Results are shown in my book Table VII-2 (p. 105). Critical concentration (milligrams of element/kg dry plant wt) for K and Mg is 8,000 and 1,000, respectively. What this means is that when E. occidentalis contained less than 8,000 ppm K, it was K deficient. When it contained less than 1,000 ppm Mg, it was Mg deficient,

I would take from this, plus knowing that K is a MAJOR plant nutrient that, yes, aquatic plants need quite a bit more K than Mg. How much more? You are all welcome to pick a number!

We can all thank Gerloff for doing this bruising set of experiments!
Many thanks for your valued reply. I apologize for my delay in getting back to you. Being new around here, I'm still getting familiar with the forum.

I will be purchasing your book within the next few days. The information that you have kindly provided is just what I was looking for. Thank you.

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Unread 03-14-2020, 02:52 PM   #9 (permalink)
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Default Re: Optimum Ca:Mg:K Ratio

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Originally Posted by kekon View Post
It also depends on sodium concentration. The more sodium the more potassium has to be dosed. Tap water usually contains 5..50 ppm of sodium. That's why some people add much more potassium with no adverse effects whilst others see some adverse effects like pale looking plants and deformed tips.
Thanks, kekon. Again, that's just the kind of data that I'm looking for.

Thank you!

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Unread 03-14-2020, 03:09 PM   #10 (permalink)
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Default Re: Optimum Ca:Mg:K Ratio

Hi Everyone,

Anyone reading this thread may wonder why I say that I'm new around here when my 'Join Date' was several years ago. Let's just say that I got lost in a maze!

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