Mg Dosing with Kalkwasser - Rule of thumb?

Mono

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I've been meaning to ask this question for a while.

As I understand it, when you dose Kalkwasser you are replacing your alk and calc but not Mg.

Of course, tanks and consumption differ, but is there any rule of thumb for dosing Mg.

So, for example, if you are dosing 1,000 ml / day of saturated Kalkwasser, what would be a good approximate (or starting point) for Mg dosing?

What would be a good Mg solution? Would the regular BRS Mg 3-part supplement work (5 1/4 c. Magnesium Chloride : 2 c. Magnesium Sulfate)?

Or is there a better solution (pun intended)?
 

D E N I N O

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I just test my Mg at the end of the month and dose aquaforest magnesium to top it up. My tanks fairly low demand, this works for me.

You could do the same but weekly if you have a higher demand tank.
 
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Mono

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I just test my Mg at the end of the month and dose aquaforest magnesium to top it up. My tanks fairly low demand, this works for me.

You could do the same but weekly if you have a higher demand tank.
Ha, that's kind of what I'm doing now when I get off my duff and test.

I was just wondering if there is a more "scientific" way to master this process.
 

Randy Holmes-Farley

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Sure, but magnesium is somewhat guesswork for every system as different organisms use more or less relative to calcium.

I added magnesium to my new salt water for water changes. That way, one could never overdose and need not worry much about measurement.

But here's one way to think of it:


"Magnesium Consumption Relative to Calcium

Calcium is present in the coral skeletons described in Table 1 at about 35 - 38% by weight, because they are largely calcium carbonate. Consequently, the Mg/Ca ratio ranges from about 0.0025 to 0.12 by weight in corals.

Consequently, for a calcium supplement to be the sole source of magnesium in an aquarium, it would have to include approximately this same Mg/Ca ratio (0.0025 to 0.12) to preclude magnesium's buildup or depletion over time. Obviously, with such a wide range, the exact balance in any given aquarium will be determined in part by the mix of corals and coralline algae being maintained. Fortunately, there is such a large reservoir of magnesium in seawater that it takes large differences between import and export to cause important changes in magnesium levels."


Thus, if you add about 1/10th as much magnesium (in ppm) as you add in calcium, that should cover the demand.

This calculator can be sued to determine how much calcium you are adding with kalkwasser, and then how much of what supplement might be used to add magnesium:

 
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Mono

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Thanks Randy.

I'm going to play around with the Ree Calculator a bit later.

Just a quick follow up question, Would you dose magnesium chloride OR a magnesium chloride + magnesium sulfide mix?

I suppose the standard BRS mix would be a bit better since it is tracks more closely to the ions present in NSW but might be a bit harder to calculate the amount of Mg.

I'm just not sure it would make much of a difference either way.

Thanks
 

Randy Holmes-Farley

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Thanks Randy.

I'm going to play around with the Ree Calculator a bit later.

Just a quick follow up question, Would you dose magnesium chloride OR a magnesium chloride + magnesium sulfide mix?

I suppose the standard BRS mix would be a bit better since it is tracks more closely to the ions present in NSW but might be a bit harder to calculate the amount of Mg.

I'm just not sure it would make much of a difference either way.

Thanks

Optimal for this purpose is my diy that is 10 parts chloride and 1 part sulfate:


3. A certain mixture of magnesium chloride and magnesium sulfate has no net effect on seawater's major anions (chloride and sulfate). All that is necessary for such a recipe is to add these two ingredients in such a ratio that they add chloride and sulfate in the ratio naturally present in seawater (which is 7.1 to 1 on a weight basis and 9.6 to 1 on a per ion basis).

To perfect such a recipe, it's imperative to know the amounts of sulfate in Epsom salts (39%), the amount of chloride in magnesium chloride hexahydrate (34.9%), and their bulk densities, because most aquarists will use a volume based measurement (1.05 g/cm3 for Epsom salts and 0.85 g/cm3 for magnesium chloride hexahydrate solids). Taking all these factors into account, the desired volume ratio is 10:1, MAG flake to Epsom salts, as a supplement; for instance, 10 cups MAG flake and 1 cup Epsom salts.
 
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Mono

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Optimal for this purpose is my diy that is 10 parts chloride and 1 part sulfate:


3. A certain mixture of magnesium chloride and magnesium sulfate has no net effect on seawater's major anions (chloride and sulfate). All that is necessary for such a recipe is to add these two ingredients in such a ratio that they add chloride and sulfate in the ratio naturally present in seawater (which is 7.1 to 1 on a weight basis and 9.6 to 1 on a per ion basis).

To perfect such a recipe, it's imperative to know the amounts of sulfate in Epsom salts (39%), the amount of chloride in magnesium chloride hexahydrate (34.9%), and their bulk densities, because most aquarists will use a volume based measurement (1.05 g/cm3 for Epsom salts and 0.85 g/cm3 for magnesium chloride hexahydrate solids). Taking all these factors into account, the desired volume ratio is 10:1, MAG flake to Epsom salts, as a supplement; for instance, 10 cups MAG flake and 1 cup Epsom salts.
Perfect!

Glad I asked.

Thanks
 

Betex

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Sure, but magnesium is somewhat guesswork for every system as different organisms use more or less relative to calcium.

I added magnesium to my new salt water for water changes. That way, one could never overdose and need not worry much about measurement.

But here's one way to think of it:


"Magnesium Consumption Relative to Calcium

Calcium is present in the coral skeletons described in Table 1 at about 35 - 38% by weight, because they are largely calcium carbonate. Consequently, the Mg/Ca ratio ranges from about 0.0025 to 0.12 by weight in corals.

Consequently, for a calcium supplement to be the sole source of magnesium in an aquarium, it would have to include approximately this same Mg/Ca ratio (0.0025 to 0.12) to preclude magnesium's buildup or depletion over time. Obviously, with such a wide range, the exact balance in any given aquarium will be determined in part by the mix of corals and coralline algae being maintained. Fortunately, there is such a large reservoir of magnesium in seawater that it takes large differences between import and export to cause important changes in magnesium levels."


Thus, if you add about 1/10th as much magnesium (in ppm) as you add in calcium, that should cover the demand.

This calculator can be sued to determine how much calcium you are adding with kalkwasser, and then how much of what supplement might be used to add magnesium:

This all makes sense but have one question I use BRS Magnesium Mix (2-part Maintenance) and have been having a hard time maintaining mag unless I dose 40ml daily while I dose 50-60 calc daily what am I doing wrong here? Or is the 2-part maintenance much less potent than the regular mix? I use your Sodium Hydroxide and the BRS for Calc/Mag
 
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Mono

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Alrighty, this is what I got....Are these numbers even close?

Or do I have to go back to school???

AdditiveIonPPMKalkwasser liters / weekCa mg / weekCa g / week
KalkwasserCa+80821808 mg/l * 21 l = 16,968 mg Ca17 g
AdditiveIonPPMMg g / week (1:10 Ratio to Ca)Mg l / weekMg ml / week
Randy's Mg Recipe
(7.25 cups MgCl2 + 0.75 cups MgSO4 in 1 gallon RODI)
Mg+47,0001.7 g1.7 g / 47 g/l = 0.036 l36 ml
 
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