Calcium - Magnesium Ratio - The Planted Tank Forum
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post #1 of 11 (permalink) Old 05-08-2020, 03:53 AM Thread Starter
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Calcium - Magnesium Ratio

Hi everyone, about 6 months ago I started my first planted aquarium so I am fairly new to this.
My tank is a 75gal low tech, sand substrate.

Recently I learned about the Calcium to Magnesium ratio that ideally it should be in the range of 3:1. I do not have Ca Mg water tests but I was able to pull the water report from my tap water supplier and here is what I found:
On average my tap water contains approximately 24ppm Ca and 14ppm Mg.

What product should I buy to raise the Ca and how can I calculate how much Ca do I need to add?

Any other suggestions ore recommendations are welcome since I am still new and learning.
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post #2 of 11 (permalink) Old 05-08-2020, 02:13 PM
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CASO4 is generally used to raise the Calcium level in an aquarium or reverse osmosis water.
This Site is generally used to determine how much of ____ to add to your tank. Not that it matters much, but I generally try to figure out how much water I am working with. In the case of your 75g tank, it is highly unlikely you will have 75g of water in there. Another good calculator tool is this site. They also have a good volume calculator to determine exactly how much water is in your tank. Depending on what you use for a filter (HOB or canister) you may need to add a few gallons for that.
With regards to the Ca:Mg ratio - I would consider it more of a goal than an absolute. Most aquarium plants will adapt to whatever you provide. Learning to know what a Ca deficiency looks like is very helpful. I suspect at 24ppm Ca you will not have a Ca issue.


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post #3 of 11 (permalink) Old 05-08-2020, 04:20 PM
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Just my opinion - there's nothing wrong with your balance. You have to remember that 3:1 is just a guideline someone said once that everyone follows.

Besides that though, what's your target GH? Adding calcium or magnesium will increase it.
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post #4 of 11 (permalink) Old 05-08-2020, 08:25 PM
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In a low tech/low plant uptake scenario it becomes less important. If doing regular water changes you really shouldn’t have to worry about either of those becoming a deficiency.

Worry more about finding the NPK and micro dosing that keeps those levels on target for your tanks uptake and you’ll be fine.
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post #5 of 11 (permalink) Old 05-18-2020, 05:34 AM Thread Starter
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My GH is about 143ppm or 8 drops on API test. My KH is about 107ppm or 6 drops on API test.

What test should I use for testing Calcium in fresh water aquarium? I saw API sells a Calcium test but it says that it's for saltwater, can it be used in fresh water?
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post #6 of 11 (permalink) Old 05-18-2020, 12:07 PM
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Quote:
Originally Posted by vanostav61 View Post
My GH is about 143ppm or 8 drops on API test. My KH is about 107ppm or 6 drops on API test.

What test should I use for testing Calcium in fresh water aquarium? I saw API sells a Calcium test but it says that it's for saltwater, can it be used in fresh water?
The API test kit for CA works very well for freshwater aquariums - with some modifications :-) Will have to dig up the method but if I remember right, you will want some type of small glass container (think 40-100ml) and a nice white paper towel or piece of paper (helps with noting the color change)


Method:
Collect 20ml of aquarium water, add 5 drops of #1 solution and mix.
Start adding 1 drop of #2 solution and mix. Watch for color change from pink to blue. (kinda subtle - you may have to try a few times to get used to how it works)
Each drop of #2 solution is equal to 5ppm CA


To determine the MG level of your aquarium, you will also need to test for General Hardness (GH)
((17.86 x dGH) - (2.5 x CA ppm))/4.1 = Mg ppm
or
(ppm dGH - (2.5 x CA ppm))/4.1 - Mg ppm
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post #7 of 11 (permalink) Old 05-18-2020, 03:45 PM Thread Starter
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Quote:
Originally Posted by Immortal1 View Post
The API test kit for CA works very well for freshwater aquariums - with some modifications :-) Will have to dig up the method but if I remember right, you will want some type of small glass container (think 40-100ml) and a nice white paper towel or piece of paper (helps with noting the color change)


Method:
Collect 20ml of aquarium water, add 5 drops of #1 solution and mix.
Start adding 1 drop of #2 solution and mix. Watch for color change from pink to blue. (kinda subtle - you may have to try a few times to get used to how it works)
Each drop of #2 solution is equal to 5ppm CA


To determine the MG level of your aquarium, you will also need to test for General Hardness (GH)
((17.86 x dGH) - (2.5 x CA ppm))/4.1 = Mg ppm
or
(ppm dGH - (2.5 x CA ppm))/4.1 - Mg ppm
Thank you! Will definitely give that a try.

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post #8 of 11 (permalink) Old 05-18-2020, 03:57 PM
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Quote:
Originally Posted by vanostav61 View Post
What test should I use for testing Calcium in fresh water aquarium? I saw API sells a Calcium test but it says that it's for saltwater, can it be used in fresh water?
I recently had the same discussion on this thread: https://www.plantedtank.net/forums/1...l#post11341067, posts #4 and #8.

Same approach as @Immortal1 mentioned, but with higher accuracy.
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post #9 of 11 (permalink) Old 05-19-2020, 02:21 AM Thread Starter
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Thank you @Deanna.

I was reviewing my water report today again and found a parameter called Bicarbonate CaCO3 average 114ppm.

I am not strong in Chemistry, does this element add to Calcium?

In any case I am attaching my water report review if anyone wants to take a look.

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File Type: pdf lincolnoaks_1589856210505.pdf (2.13 MB, 3 views)
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post #10 of 11 (permalink) Old 05-19-2020, 03:45 AM
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Quote:
Originally Posted by vanostav61 View Post
Thank you @Deanna.

I was reviewing my water report today again and found a parameter called Bicarbonate CaCO3 average 114ppm.

I am not strong in Chemistry, does this element add to Calcium?

In any case I am attaching my water report review if anyone wants to take a look.

Sent from my SM-G975U using Tapatalk
That would not contribute to your Ca. It affects your alkalinity (KH).

Others may open that file, but I'm hesitant to open an unknown file. If you have a reading for calcium and magnesium in it, then you can see the ratio.
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post #11 of 11 (permalink) Old 05-19-2020, 03:51 AM Thread Starter
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Quote:
Originally Posted by Deanna View Post
That would not contribute to your Ca. It affects your alkalinity (KH).



Others may open that file, but I'm hesitant to open an unknown file. If you have a reading for calcium and magnesium in it, then you can see the ratio.
That's enough to know, thank you.

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