Calcium and magnesium? - The Planted Tank Forum
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post #1 of 16 (permalink) Old 01-23-2006, 07:31 PM Thread Starter
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Calcium and magnesium?

Can you tell me if my readings from my tap are fine or do i need to supplement.
Calcium 77 ppm
Magnesium 29 ppm

Also, no iron detected from my tap, should i dose extra iron then?, thanks
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post #2 of 16 (permalink) Old 01-23-2006, 07:57 PM
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You have a dGH of 17.44; which is hard, but it's fine. No need for extra Ca or Mg. How did you test for Mg? I haven't found a FW Mg test kit yet.
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post #3 of 16 (permalink) Old 01-24-2006, 12:13 AM Thread Starter
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I meant from my recent water supply analysis, i assume that's what comes out of the tap.
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post #4 of 16 (permalink) Old 01-24-2006, 03:11 AM
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From my current understanding, if you have lots of stunted new growth, you are likely Ca deficient (or, as in my case, a lack of a micro nutrient is causing Ca to be 'blocked'). If you are losing lots of bottom/older leaves, you could be Mg deficient.

Sounds like you are in a good range, but in case it applies...
Brian.
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post #5 of 16 (permalink) Old 01-25-2006, 06:55 PM
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Quote:
Originally Posted by Raul-7
You have a dGH of 17.44; which is hard, but it's fine. No need for extra Ca or Mg. How did you test for Mg? I haven't found a FW Mg test kit yet.
How did you come up with that figure?

I thought total hardness would be 77 + 29 = 106 ppm = 5.9 dGH

Regards,
Barry
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post #6 of 16 (permalink) Old 01-25-2006, 06:59 PM
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Quote:
Originally Posted by tiny
Can you tell me if my readings from my tap are fine or do i need to supplement.
Calcium 77 ppm
Magnesium 29 ppm

Also, no iron detected from my tap, should i dose extra iron then?, thanks
If you are just reading your water report, does your water pass through a home water softener unit?

My city water report says:

CaCO3 as Calcium - 236
CaCO3 as Magnesium - 167

Total Hardness: 236 + 167 = 403 ppm (mg/L) = 22.5 dGH

My water passes through a water softener that changes Calcium for Sodium so my GH test kit indicates 70 ppm or about 4 dGH.

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Barry
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post #7 of 16 (permalink) Old 01-26-2006, 08:16 PM Thread Starter
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Not using water softener, i guess that's good in my case.
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post #8 of 16 (permalink) Old 01-26-2006, 11:18 PM
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Quote:
Originally Posted by tiny
Not using water softener, i guess that's good in my case.
At any rate, your water is SOFT, not hard.

Quote:
General Hardness (GH)
General hardness (GH) refers to the dissolved concentration of magnesium and calcium ions. When fish are said to prefer ``soft'' or ``hard'' water, it is GH (not KH) that is being referred to.

Note: GH, KH and pH form the Bermuda's Triangle of water chemistry. Although the three properties are distinct, they all interact with each other to varying degrees, making it difficult to adjust one without impacting the other. That is one reason why beginning aquarists are advised NOT to tamper with these parameters unless absolutely necessary. As an example, ``hard'' water frequently often comes from limestone aquifers. Limestone contains calcium carbonate, which when dissolved in water increases both the GH (from calcium) and KH (from carbonate) components. Increasing the KH component also usually increases pH as well. Conceptually, the KH acts as a ``sponge'' absorbing the acid present in the water, raising the water's pH.

Water hardness follows the following guidelines. The unit dH means ``degree hardness'', while ppm means ``parts per million'', which is roughly equivalent to mg/L in water. 1 unit dH equals 17.8 ppm CaCO3. Most test kits give the hardness in units of CaCO3; this means the hardness is equivalent to that much CaCO3 in water but does not mean it actually came from CaCO3.

General Hardness

0 - 4 dH, 0 - 70 ppm : very soft
4 - 8 dH, 70 - 140 ppm : soft
8 - 12 dH, 140 - 210 ppm : medium hard
12 - 18 dH, 210 - 320 ppm : fairly hard
18 - 30 dH, 320 - 530 ppm : hard
higher : liquid rock (Lake Malawi and Los Angeles, CA)
Source: http://faq.thekrib.com/begin-chem.html

Regards,
Barry
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post #9 of 16 (permalink) Old 01-27-2006, 06:53 AM
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Quote:
Originally Posted by banderbe
How did you come up with that figure?

I thought total hardness would be 77 + 29 = 106 ppm = 5.9 dGH
The formula is: dGH = (4.1 x Mg ppm) + (2.5 x Ca ppm) / 17.86
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post #10 of 16 (permalink) Old 01-27-2006, 12:11 PM
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Quote:
Originally Posted by Raul-7
The formula is: dGH = (4.1 x Mg ppm) + (2.5 x Ca ppm) / 17.86
But isn't dGH also equal to the Total Hardness in ppm / 17.8 ?

I wonder where you got your info from.. not saying you're wrong.. maybe I am.. just want to learn more!

And according to my water report the Mg and Ca as CaCO3 values added together equal the total hardness.

According to your formula, and using the values in my city's water report, my water has a dGH of 71.3 which is just over twice as hard as the water in Lake Malawi. Not bloody likely.

Something is wrong with this picture and it's either my water report or your formula.

Regards,
Barry
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post #11 of 16 (permalink) Old 01-27-2006, 03:42 PM
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Quote:
Originally Posted by banderbe
But isn't dGH also equal to the Total Hardness in ppm / 17.8 ?
His formula is for readings which are not in a CaCO3 equivalence.

EDTA hardness chelation tests read in an equivalent of CaCO3. That means when you do a GH test and get an "as CaCO3" ppm reading, it means, "if the only thing dissolved in the water is CaCO3, this is how much CaCO3 there would be in ppm."

"Degrees of German Hardness" is a standard that is equal to 10 ppm of calcium oxide.

Calcium weighs 40.078 grams per mole. Oxygen weighs 15.9994 grams per mole. Therefore, a degree of German Hardness is 71.46908 % calcium and 28.53092 % oxygen, or 7.146908 ppm of calcium.

Since GH test readings are in CaCO3 equivalence, you have to account for the amount of carbonate that will be present along with the 7.146908 ppm of calcium. Carbonate weighs 60.0089 grams per mole. Therefore, calcium carbonate is 40.04320 % calcium, and you would need 2.497303 milligrams of calcium carbonate to raise the calcium content of the water by 1 ppm per liter. (1 / .4004230). Since we know a degree contains 7.146908 ppm of calcium, then 2.497303 x 7.146908 = 17.847993 ppm of calcium carbonate in 1 degree.

There are different ways to apply this to tiny's readings. If the readings are not already in a CaCO3 equivalence, then we don't know exactly what all the calcium compounds are in his water. What Raul-7 posted is a way to translate everything over to calcium carbonate. (That's one of the things I like about using RO/DI water... you actually know and control what compounds the GH comes from.) If tiny's calcium levels are 77 ppm, then you would need 192.29233 ppm of CaCO3 to achieve that level of calcium.

Another thing about GH tests is that magnesium cations react the same on these tests as calcium cations do. The atomic weight of magnesium is 24.305 grams per mole. That's 60.64424 % of what calcium weighs. Since 1 degree of hardness for calcium is 7.146908 ppm, then 60.64424 % of that is 4.33419 ppm of magnesium in 1 degree of German hardness.

Again, applying this to tiny's magnesium reading of 29 ppm as a calcium carbonate equivalence is a bit of a conundrum, since we are assuming that the magnesium containing compound that is present is calcium carbonate, which of course contains no magnesium.

Since it takes 1.64896 times as much magnesium to make the GH test read 1 ppm as CaCO3 (40.078 / 24.305), we need to multiply the 2.497303 milligrams of CaCO3 it takes to raise calcium by 1 ppm by 1.64896, which equals 4.11796. So 29 ppm of magnesium as read as calcium carbonate on a GH test would equal to 119.42084 ppm.

The 119.42084 ppm + 192.29233 ppm = 311.71317 ppm of CaCO3, or 17.46489 degrees.

To get a much better idea of the actual "total hardness," you would really want to take a TDS (total dissolved solids) reading using a conductivity meter.

If tiny's water report is like yours (and it probably is), then the readings are already in a CaCO3 equivalence, and the above does not apply. In that case, the GH would be 108 ppm as CaCO3, which is 6.05110 degrees of German hardness, with a 2.65517:1 calcium:magnesium ratio.
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post #12 of 16 (permalink) Old 01-27-2006, 05:48 PM
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Quote:
Originally Posted by Hypancistrus
His formula is for readings which are not in a CaCO3 equivalence.
Thanks, that was very informative.

Can I use that information to figure out my Ca/Mg amounts in my water after it passes through my water softener?

My GH test says the "softened" water contains 70ppm.

Regards,
Barry
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post #13 of 16 (permalink) Old 01-28-2006, 11:04 PM Thread Starter
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So, Am i okay with my tap and not need to add calcium and magnesium?
btw, the tap PH is 7.7
Also, my tank water GH is tested 380 ppm.
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post #14 of 16 (permalink) Old 02-08-2006, 06:58 PM
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Quote:
Originally Posted by Hypancistrus
His formula is for readings which are not in a CaCO3 equivalence.

EDTA hardness chelation tests read in an equivalent of CaCO3. That means when you do a GH test and get an "as CaCO3" ppm reading, it means, "if the only thing dissolved in the water is CaCO3, this is how much CaCO3 there would be in ppm."

"Degrees of German Hardness" is a standard that is equal to 10 ppm of calcium oxide.

Calcium weighs 40.078 grams per mole. Oxygen weighs 15.9994 grams per mole. Therefore, a degree of German Hardness is 71.46908 % calcium and 28.53092 % oxygen, or 7.146908 ppm of calcium.

Since GH test readings are in CaCO3 equivalence, you have to account for the amount of carbonate that will be present along with the 7.146908 ppm of calcium. Carbonate weighs 60.0089 grams per mole. Therefore, calcium carbonate is 40.04320 % calcium, and you would need 2.497303 milligrams of calcium carbonate to raise the calcium content of the water by 1 ppm per liter. (1 / .4004230). Since we know a degree contains 7.146908 ppm of calcium, then 2.497303 x 7.146908 = 17.847993 ppm of calcium carbonate in 1 degree.

There are different ways to apply this to tiny's readings. If the readings are not already in a CaCO3 equivalence, then we don't know exactly what all the calcium compounds are in his water. What Raul-7 posted is a way to translate everything over to calcium carbonate. (That's one of the things I like about using RO/DI water... you actually know and control what compounds the GH comes from.) If tiny's calcium levels are 77 ppm, then you would need 192.29233 ppm of CaCO3 to achieve that level of calcium.

Another thing about GH tests is that magnesium cations react the same on these tests as calcium cations do. The atomic weight of magnesium is 24.305 grams per mole. That's 60.64424 % of what calcium weighs. Since 1 degree of hardness for calcium is 7.146908 ppm, then 60.64424 % of that is 4.33419 ppm of magnesium in 1 degree of German hardness.

Again, applying this to tiny's magnesium reading of 29 ppm as a calcium carbonate equivalence is a bit of a conundrum, since we are assuming that the magnesium containing compound that is present is calcium carbonate, which of course contains no magnesium.

Since it takes 1.64896 times as much magnesium to make the GH test read 1 ppm as CaCO3 (40.078 / 24.305), we need to multiply the 2.497303 milligrams of CaCO3 it takes to raise calcium by 1 ppm by 1.64896, which equals 4.11796. So 29 ppm of magnesium as read as calcium carbonate on a GH test would equal to 119.42084 ppm.

The 119.42084 ppm + 192.29233 ppm = 311.71317 ppm of CaCO3, or 17.46489 degrees.

To get a much better idea of the actual "total hardness," you would really want to take a TDS (total dissolved solids) reading using a conductivity meter.

If tiny's water report is like yours (and it probably is), then the readings are already in a CaCO3 equivalence, and the above does not apply. In that case, the GH would be 108 ppm as CaCO3, which is 6.05110 degrees of German hardness, with a 2.65517:1 calcium:magnesium ratio.

Thanks that was very informative. So if water that has passed through my water softener has a GH of 5, then using your formulas I can conclude that this "softened" water has 5*17.847993 = 89 ppm of Calcium carbonate, right? That means that this water has 89 *0.4004230 = 35.7 ppm Calcium. Correct?

Thanks again.

Regards,
Barry
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post #15 of 16 (permalink) Old 02-08-2006, 11:10 PM
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Tiny, most likely you do not need to add calcium and magnesium, unless you have certain, hard water loving plants.
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