How much calcium and magnesium is this? - The Planted Tank Forum
 
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post #1 of 9 (permalink) Old 09-19-2014, 05:46 AM Thread Starter
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How much calcium and magnesium is this?

Not too long ago, I bought an API test kit to test for my fish tank GH. It took me 16 drops to get the color of my fish tank water sample to change color, meaning that my GH should be at 16.

My understanding is that GH is a combination of calcium and magnesium. Based on that number 16, how am I supposed to figure out how much calcium or magnesium there is on my water, well besides looking at my city water report?


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post #2 of 9 (permalink) Old 09-19-2014, 06:29 AM
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I'm sure that someone who knows how to tell you that will answer before too long.
But I dose those and only need to use 5 drops to get the color to change even/w the dosing.
But here is a thought for you. If you are in the same town/city as the place where you might get fish from...they already have gotten used to that water if you and the pet shop are both on the city water.

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post #3 of 9 (permalink) Old 09-19-2014, 07:18 AM
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There is no way to tell just from the GH measuurement.
Your local water works should be able to give you the numbers. You could also buy a Magnesium water test kit. I know JBL has one. I'm guessing you want to have a good ratio of Magnesium to Calcium for your plants, which is a good approach. You have pretty hard water at a GH of 16 if that is directly from your tap.

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post #4 of 9 (permalink) Old 09-19-2014, 06:44 PM
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Quote:
Originally Posted by kidgrave View Post
Not too long ago, I bought an API test kit to test for my fish tank GH. It took me 16 drops to get the color of my fish tank water sample to change color, meaning that my GH should be at 16.

My understanding is that GH is a combination of calcium and magnesium. Based on that number 16, how am I supposed to figure out how much calcium or magnesium there is on my water, well besides looking at my city water report?

Buy a Ca test kit, determine the amount of Ca in the water....the difference is Mg.


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post #5 of 9 (permalink) Old 09-19-2014, 09:41 PM Thread Starter
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Originally Posted by Ghia View Post
There is no way to tell just from the GH measuurement.
Your local water works should be able to give you the numbers. You could also buy a Magnesium water test kit. I know JBL has one. I'm guessing you want to have a good ratio of Magnesium to Calcium for your plants, which is a good approach. You have pretty hard water at a GH of 16 if that is directly from your tap.
Yep, that is directly from my tap. I'm saving money for a co2 regulator, so I think I'll just call my local water works, lol. When it comes to having a GH of 16, is it possible to have a lot of calcium and very low magnesium, or a lot of magnesium and very low calcium?

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Originally Posted by Raymond S. View Post
I'm sure that someone who knows how to tell you that will answer before too long.
But I dose those and only need to use 5 drops to get the color to change even/w the dosing.
But here is a thought for you. If you are in the same town/city as the place where you might get fish from...they already have gotten used to that water if you and the pet shop are both on the city water.
I buy my fish from my local petshop, which is 4 minutes away. They are mostly a salt water store, and they are always testing their water parameters. I will ask them about my water supply when I go visit them.


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post #6 of 9 (permalink) Old 09-20-2014, 01:11 AM
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is it possible to have a lot of calcium and very low magnesium, or a lot of magnesium and very low calcium?
Possible, but rare.
The water does not have to have Ca and Mg in the exact ratio that plants or fish use. Plants use roughly 4 parts Ca to 1 part Mg, but if the water is anywhere around there, that is fine.

Do a bit more research if you have to do the tests yourself.
There is a bit of a formula to use when you are trying to figure out how much of each you have.

Test GH.
Test Ca.
The Mg is NOT simply GH - Ca.
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post #7 of 9 (permalink) Old 09-20-2014, 09:03 AM
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Originally Posted by Diana View Post
Test GH.
Test Ca.
The Mg is NOT simply GH - Ca.
That is why I recommended a Magnesium test kit rather than a Calcium one.

The "composition" of your GH will vary according to
1. What kind of groundminerals are in the area where the water works collect their raw water. Dolomite type minerals will mean more Mg.
2. How the water works actually treat the water, i.e. what they add or subtract.

For ease of approach, GH is often cited as being Ca+Mg. But, as Diana says, that is not actually the whole truth. GH is mainly composed of Ca+Mg, but per definition it is the sum of all multi-valent mineral cations. So, there may be other multivalent mineral ions which also contribute towards the total GH, but normally they are found in lesser concentrations and therefore not taken into account.

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post #8 of 9 (permalink) Old 09-20-2014, 10:31 AM
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Quote:
Originally Posted by Ghia View Post
That is why I recommended a Magnesium test kit rather than a Calcium one.

The "composition" of your GH will vary according to
1. What kind of groundminerals are in the area where the water works collect their raw water. Dolomite type minerals will mean more Mg.
2. How the water works actually treat the water, i.e. what they add or subtract.

For ease of approach, GH is often cited as being Ca+Mg. But, as Diana says, that is not actually the whole truth. GH is mainly composed of Ca+Mg, but per definition it is the sum of all multi-valent mineral cations. So, there may be other multivalent mineral ions which also contribute towards the total GH, but normally they are found in lesser concentrations and therefore not taken into account.
"...but normally they are found in lesser concentrations and therefore not taken into account."

Exactly, so: Gh-Ca=Mg is generally sufficient for our purposes.


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post #9 of 9 (permalink) Old 09-23-2014, 07:19 PM
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Quote:
Originally Posted by kidgrave View Post
Not too long ago, I bought an API test kit to test for my fish tank GH. It took me 16 drops to get the color of my fish tank water sample to change color, meaning that my GH should be at 16.
>>>
The Ca/Mg ratio asides, API GH test kit goes bad fast.
It would report higher and higher GH (and harder to
distinguish the color) overtime as the reagent approaches
the expiration date. I wouldn't trust it.

BTW, the KH part is very good and has long shelf life.
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