Help me understand Ca/Mg amount vs. ppm - Page 2 - The Planted Tank Forum
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post #16 of 39 (permalink) Old 07-14-2020, 04:19 AM Thread Starter
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Your dGH is fine for plants, although many of us are lower. Your Ca and Mg dosing lines up with a dGH of about 7. If you actually dosed to reach your above-mentioned 15ppm Ca and 5ppm Mg, your dGH would be 3.25, which would be my preference and, remember, you have to adjust dosing to target when you do water changes, e.g.; if you do a 50% water change, then you add back 50% of the initial dose plus any lost to uptake. This requires testing for Ca and Mg to be more certain. If you are interested in this testing, let me know and I'll give you the detail of how to do it.

You may want to download this calculator: Zorfox's Planted Tank Calculator. In addition to doing the same type of calculations as RotalaButterfly, it also has a GH calculator, which would answer many of your questions.

Regarding how much K to dose. Yes, given the 35ppm Ca, I would dose to reach about 40ppm K, if you want to maintain that Ca level. Some members are ok matching the Ca level with K.

When building the ratios, you have to use ppm, since the dGH doesn't work the same way as the raw ppm numbers.
Great.. Thanks again. I feel like I'm finally getting a grasp on all these calculations. Regarding the Ca:Mg:K ratio, is this something I should tweak based on what plants I have and how they respond, or should I stick with the 1:1 Ca:K? Any comment(s) on why that Aquasabi article said 2:1:0.5 is an ideal ratio?

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post #17 of 39 (permalink) Old 07-14-2020, 06:45 PM Thread Starter
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Your dGH is fine for plants, although many of us are lower. Your Ca and Mg dosing lines up with a dGH of about 7. If you actually dosed to reach your above-mentioned 15ppm Ca and 5ppm Mg, your dGH would be 3.25, which would be my preference and, remember, you have to adjust dosing to target when you do water changes, e.g.; if you do a 50% water change, then you add back 50% of the initial dose plus any lost to uptake. This requires testing for Ca and Mg to be more certain. If you are interested in this testing, let me know and I'll give you the detail of how to do it.

You may want to download this calculator: Zorfox's Planted Tank Calculator. In addition to doing the same type of calculations as RotalaButterfly, it also has a GH calculator, which would answer many of your questions.

Regarding how much K to dose. Yes, given the 35ppm Ca, I would dose to reach about 40ppm K, if you want to maintain that Ca level. Some members are ok matching the Ca level with K.

When building the ratios, you have to use ppm, since the dGH doesn't work the same way as the raw ppm numbers.
Yes, I would like to know how to test the calcium and magnesium in my source water (50/50 tap/RO) to have a baseline.

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post #18 of 39 (permalink) Old 07-14-2020, 10:54 PM Thread Starter
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Originally Posted by Deanna View Post
Your dGH is fine for plants, although many of us are lower. Your Ca and Mg dosing lines up with a dGH of about 7. If you actually dosed to reach your above-mentioned 15ppm Ca and 5ppm Mg, your dGH would be 3.25, which would be my preference and, remember, you have to adjust dosing to target when you do water changes, e.g.; if you do a 50% water change, then you add back 50% of the initial dose plus any lost to uptake. This requires testing for Ca and Mg to be more certain. If you are interested in this testing, let me know and I'll give you the detail of how to do it.

You may want to download this calculator: Zorfox's Planted Tank Calculator. In addition to doing the same type of calculations as RotalaButterfly, it also has a GH calculator, which would answer many of your questions.

Regarding how much K to dose. Yes, given the 35ppm Ca, I would dose to reach about 40ppm K, if you want to maintain that Ca level. Some members are ok matching the Ca level with K.

When building the ratios, you have to use ppm, since the dGH doesn't work the same way as the raw ppm numbers.
Yes, I would like to know how to test the calcium and magnesium in my source water (50/50 tap/RO) to have a baseline.

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post #19 of 39 (permalink) Old 07-15-2020, 01:37 AM
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Yes, I would like to know how to test the calcium and magnesium in my source water (50/50 tap/RO) to have a baseline.
Using the API GH/KH and Calcium (saltwater) kits, you test Ca and GH and then derive Mg with this process.

GH - the kit uses a 5ml water sample. Much greater precision can be obtained by using a 25ml water sample with the resulting number of drops then being divided by 5.

Ca - the kit is designed for saltwater, so some modification is needed for freshwater use. I use a 50ml sample in order to allow each final reagent drop to equal 2ppm of Ca. The procedure is then:
1) Add 20 drops of reagent #1 & mix.
2) Shake reagent #2 for 15 seconds before each test.
3) Add 1 drop at a time of reagent #2 and mix. Multiply the number of drops of reagent #2 by 2 and the result is the Ca ppm.

MG - using the GH and Ca results, plug the numbers into the following formula to derive the Mg ppm (note that 1 degree GH = 17.86ppm):
(GH ppm – 2.5 x Ca ppm) / 4.1

For the modifed tests, mentioned above, larger test tubes need to be purchased, such as this one: https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

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Originally Posted by mossman77 View Post
Great.. Thanks again. I feel like I'm finally getting a grasp on all these calculations. Regarding the Ca:Mg:K ratio, is this something I should tweak based on what plants I have and how they respond, or should I stick with the 1:1 Ca:K? Any comment(s) on why that Aquasabi article said 2:1:0.5 is an ideal ratio?
It is not necessary to tailor Ca and Mg to specific plants and I have no idea why that Aquasabi ratio is suggested. Are you sure it wasn't K:Ca:Mg? That would make much more sense.

Last edited by Deanna; 07-15-2020 at 02:04 AM. Reason: Respond to additional post
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post #20 of 39 (permalink) Old 07-15-2020, 03:16 AM Thread Starter
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Originally Posted by mossman77 View Post
Yes, I would like to know how to test the calcium and magnesium in my source water (50/50 tap/RO) to have a baseline.
Using the API GH/KH and Calcium (saltwater) kits, you test Ca and GH and then derive Mg with this process.

GH - the kit uses a 5ml water sample. Much greater precision can be obtained by using a 25ml water sample with the resulting number of drops then being divided by 5.

Ca - the kit is designed for saltwater, so some modification is needed for freshwater use. I use a 50ml sample in order to allow each final reagent drop to equal 2ppm of Ca. The procedure is then:
1) Add 20 drops of reagent #1 & mix.
2) Shake reagent #2 for 15 seconds before each test.
3) Add 1 drop at a time of reagent #2 and mix. Multiply the number of drops of reagent #2 by 2 and the result is the Ca ppm.

MG - using the GH and Ca results, plug the numbers into the following formula to derive the Mg ppm (note that 1 degree GH = 17.86ppm):
(GH ppm – 2.5 x Ca ppm) / 4.1

For the modifed tests, mentioned above, larger test tubes need to be purchased, such as this one: https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

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Originally Posted by mossman77 View Post
Great.. Thanks again. I feel like I'm finally getting a grasp on all these calculations. Regarding the Ca:Mg:K ratio, is this something I should tweak based on what plants I have and how they respond, or should I stick with the 1:1 Ca:K? Any comment(s) on why that Aquasabi article said 2:1:0.5 is an ideal ratio?
It is not necessary to tailor Ca and Mg to specific plants and I have no idea why that Aquasabi ratio is suggested. Are you sure it wasn't K:Ca:Mg? That would make much more sense.
Thank you for that information!

Here's the article I'm referring to (last sentence in "the ratio" section): https://www.aquasabi.com/aquascaping...-and-magnesium

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post #21 of 39 (permalink) Old 07-15-2020, 03:58 AM
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Here's the article I'm referring to (last sentence in "the ratio" section): https://www.aquasabi.com/aquascaping...-and-magnesium
I don't think that I could trust that site. Ca can interfere with K uptake, which would make me concerned that having so much Ca, relative to K, might starve the plants for K.
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post #22 of 39 (permalink) Old 07-15-2020, 12:07 PM
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I don't think that I could trust that site. Ca can interfere with K uptake, which would make me concerned that having so much Ca, relative to K, might starve the plants for K.
"It is recommended that the content of magnesium be higher than that of potassium. This is termed as the calcium-magnesium-potassium ratio, which ideally lies in the range of 2:1:0.5"

First time I have ever read this. Not saying they are wrong, but, I am pretty sure most of the successful growers on this board would disagree. If you look at the details of a very popular product like Seachem Equilibrium you will find it is very high in K when compared to Mg.
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post #23 of 39 (permalink) Old 07-17-2020, 03:06 PM
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To help out a bit with your questions. Once you become familiar with Rotabutterfly you will probably wonder how you ever got by without it.
To begin, you mentioned re-minerilizing your RO water. Do you use something to contain the RO water before adding it to your aquarium? (I do, 55g plastic drum). If so, follow along;
In Rotalabutterfly the first thing you are asked to do is input your aquarium size (or size of your RO water container). Lets use 55 gallons.

Then answer if DIY or pre-mixed. (Generally I do DIY. But if you are using something that is pre-mixed like Equalibrium then you would answer pre-mixed)
After answering DIY, you are asked to select your compound.
Calcium (Ca) powder from the various suppliers is CaSo4.2H2O.

Magnesium (Mg) crystals from the various suppliers is MgSo4.7H2O.
Sodium Bicarbonate (Baking Soda) is NaHCO3 (I have used this in the past, but the plants don't / can't really use the NaH)(The CO3 is what raises your dKH)
Potassium Bicarbonate (Amazon) is K2CO3 (I am now using this as the plants can use the potassium)(The CO3 is what raises your dKH)

Each of the above can be selected (as a compound) in Rotalabutterfly individually. Lets try MgSO4.7H2O. Then select Dry Dosing as you will be adding the crystals to your RO container.
Now you are asked "I am Calculating For:" - Select "Dose to reach a target". I selected 10ppm. Aiming for a 2:1 ratio of Ca:Mg
Now hit the calculate button.
On the right side of the screen it will tell you how many grams automatic watches or units of measure to add to your RO container / aquarium to reach your target.


As you can see, it also lists the Mg, S, and dGH amounts. I typically use a spreadsheet to calculate how the individual amounts add up. For example, you should have been given a dGH of 2.31. If I change my compound to CaSo4.2H2O and set my target to 20ppm I will get a dGH of 2.8. So, adding these 2 compounds to your RO water will increase your dGH by 5.11.

Hope the above helps.
it really help very nice....
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post #24 of 39 (permalink) Old 07-19-2020, 04:15 PM Thread Starter
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Yes, I would like to know how to test the calcium and magnesium in my source water (50/50 tap/RO) to have a baseline.
Using the API GH/KH and Calcium (saltwater) kits, you test Ca and GH and then derive Mg with this process.

GH - the kit uses a 5ml water sample. Much greater precision can be obtained by using a 25ml water sample with the resulting number of drops then being divided by 5.

Ca - the kit is designed for saltwater, so some modification is needed for freshwater use. I use a 50ml sample in order to allow each final reagent drop to equal 2ppm of Ca. The procedure is then:
1) Add 20 drops of reagent #1 & mix.
2) Shake reagent #2 for 15 seconds before each test.
3) Add 1 drop at a time of reagent #2 and mix. Multiply the number of drops of reagent #2 by 2 and the result is the Ca ppm.

MG - using the GH and Ca results, plug the numbers into the following formula to derive the Mg ppm (note that 1 degree GH = 17.86ppm):
(GH ppm – 2.5 x Ca ppm) / 4.1

For the modifed tests, mentioned above, larger test tubes need to be purchased, such as this one: https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

Quote:
Originally Posted by mossman77 View Post
Great.. Thanks again. I feel like I'm finally getting a grasp on all these calculations. Regarding the Ca:Mg:K ratio, is this something I should tweak based on what plants I have and how they respond, or should I stick with the 1:1 Ca:K? Any comment(s) on why that Aquasabi article said 2:1:0.5 is an ideal ratio?
It is not necessary to tailor Ca and Mg to specific plants and I have no idea why that Aquasabi ratio is suggested. Are you sure it wasn't K:Ca:Mg? That would make much more sense.
I just noticed the API saltwater kit says it accurately measures Ca levels between 0 and 4 ppm. That's only 0.5 dGH.

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post #25 of 39 (permalink) Old 07-19-2020, 04:57 PM
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MgSO4.7H2O
Means 7 molecules of water are bound to the MgSO4.
Practical meaning is it weighs 7 water molecules more than MgSO4 non-hydrated.

You need to account for the water weight to determine the actual amount of Mg..

Maybe this was mentioned before..
120.366 g/mol MgSO4
246.47 g/mol MgSO4 . 7H2O

Hydrated form has 1/2 the magnesium as the non-hydrated form on a gram to gram basis approx..

Quote:
Magnesium sulfate is a chemical compound, a salt with the formula MgSO
4, consisting of magnesium cations Mg2+
(20.19% by mass)
1g MgSO4 = .2019G Mg
.1008g Mg in a gram of MgSO4.7H2O (Epsom salt)

48.8% would be more exact than 50%

IF I remember my chemistry right.. Big if.


100.8 mg/gram of epsom salts
1 gram in 36gal (est of 40gal tank) 136.3L
100.8/136.3 = 0.740ppm..
To ADD 5ppm = 6.75 Grams.. Nobody should use spoons..
Checked calcs here..
https://www.flowgrow.de/db/calculato...5Bdose%5D=6.75

https://aquariumscience.org/index.ph...-in-the-water/

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post #26 of 39 (permalink) Old 07-19-2020, 06:51 PM
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I just noticed the API saltwater kit says it accurately measures Ca levels between 0 and 4 ppm. That's only 0.5 dGH.
I don't understand the point.
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post #27 of 39 (permalink) Old 07-20-2020, 01:19 AM Thread Starter
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I just noticed the API saltwater kit says it accurately measures Ca levels between 0 and 4 ppm. That's only 0.5 dGH.
I don't understand the point.
Sorry, it was a question. If the kit only measures up to 4ppm of Ca and 4ppm of Ca is just over 1dGH, then how do I measure levels higher than that? For instance, my 50/50 tap/RO source water has a gH of 3 to begin with, which is already outside the limits of the kit. Or am I confusing Ca and CaSO4?

The Amazon listing must be wrong. I viewed the instructions on the API website and it measures from 20 ppm and up to 520 ppm in 20 ppm increments. So now the question is, how many ppm of Ca equals 1 dGH? I know 1 dGH of CaS04 is 7.144 ppm.

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post #28 of 39 (permalink) Old 07-20-2020, 01:37 AM
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Sorry, it was a question. If the kit only measures up to 4ppm of Ca and 4ppm of Ca is just over 1dGH, then how do I measure levels higher than that? For instance, my 50/50 tap/RO source water has a gH of 3 to begin with, which is already outside the limits of the kit. Or am I confusing Ca and CaSO4?
Use the modification I outlined in post #19.
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post #29 of 39 (permalink) Old 07-20-2020, 03:31 PM Thread Starter
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Sorry, it was a question. If the kit only measures up to 4ppm of Ca and 4ppm of Ca is just over 1dGH, then how do I measure levels higher than that? For instance, my 50/50 tap/RO source water has a gH of 3 to begin with, which is already outside the limits of the kit. Or am I confusing Ca and CaSO4?
Use the modification I outlined in post #19.
Can you help me understand how exactly this works as described? How does increasing the sample size by a factor of 10 and doubling solution #1 result in an accurate test? Doesn't the test rely on the ratio of solution #2 to solution #1 vs. the concentration of Ca in the sample? Each drop of solution #2 with respect to 10 drops of solution #1 represents a 20ppm increase, so I don't see how doubling sol#1 can result in a tenfold increase in resolution (2ppm).

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Last edited by mossman77; 07-20-2020 at 05:50 PM.
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post #30 of 39 (permalink) Old 07-20-2020, 10:40 PM
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Can you help me understand how exactly this works as described? How does increasing the sample size by a factor of 10 and doubling solution #1 result in an accurate test? Doesn't the test rely on the ratio of solution #2 to solution #1 vs. the concentration of Ca in the sample? Each drop of solution #2 with respect to 10 drops of solution #1 represents a 20ppm increase, so I don't see how doubling sol#1 can result in a tenfold increase in resolution (2ppm).
Solution one more or less stabilizes the sample so that solution 2 can do it's job. Regarding the variations with solution 2, the math does work out, but you can prove it to yourself by calibrating the test with Ca only, in distilled/RO water, and take readings on Ca and GH. you would then see that, for x level of Ca added, the GH reading matches correctly.
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