cb684
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- Apr 28, 2015
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- Mississippi
A good discussion started as a off topic subject in another thread.
I will transcribe some of the discussion so we can continue it here:
The discussion was on if Magnesium (chloride and sulfate) would need to be dosed even if its concentration was adequate.
@iiluisii
Residual Ions from the Calcium and Alkalinity Parts
Adding 1 gallon of each of these additives will result in a residue of ions remaining after calcification. These are mostly sodium and chloride, and the amounts of those two added are equal in numbers (i.e., moles), but slightly different in weight-based concentrations such as ppm because they do not weigh the same.
After adding 594 grams of baking soda (1 gallon of Recipe #1), we will have added 163 grams of sodium. In natural seawater, magnesium is present at about 12.0% of the sodium concentration (by weight). In order to match the magnesium additions to the sodium additions to leave them in a natural ratio, we need to add 12% of 163 grams, or 19.5 grams, of magnesium for every gallon of the two-part additive that we add.
Additionally, we may want to account for magnesium that is actually incorporated into the coral skeletons. For this calculation, I have assumed that the amount of magnesium incorporated is about 6.5% of the calcium level (by weight), or about 2.5% of the skeleton by weight. In the course of adding this gallon of both parts of the two part supplement, we added 141 grams of calcium, so we need to add 0.065 x 141 = 9 grams of magnesium to account for this deposition.
The magnesium parts of the recipe are designed to add enough magnesium so that it is not depleted by either of the two means described above. Because the magnesium supplement (either version) is 47,000 mg/L in magnesium, we need to add (9 +19.5) grams/47 g/L = 610 ml of the magnesium solution for each gallon of the other parts of Recipe #1.
cb684:
These added sodium and chloride ions will with time increase the salinity of the tank. As we add RODI water and do water changes, we adjust the salinity and end up diluting sodium, chloride and magnesium. As time passes, that and consumption will cause magnesium concentration in the water to decrease. When it decreases you add more. That is why IMO it does not make sense to add magnesium if concentration is adequate.
The rate one would need to add magnesium would be about what you said in your post in a tank where there were no other sources of magnesium. But that is not completely true for many tanks because during water changes part of the water with inadequate proportion of sodium, chloride and magnesium is exported, and water with adequate magnesium concentration (sometimes on the upper range) is added correcting its depletion. So if salinity is between 1.025 and 1.026, and magnesium is 1200 - 1400 the proportion between sodium, chloride, and magnesium is correct in spite of the amount of sodium carbonate and calcium chloride added.
@Nowell
@reefwiser
I will transcribe some of the discussion so we can continue it here:
The discussion was on if Magnesium (chloride and sulfate) would need to be dosed even if its concentration was adequate.
@iiluisii
Residual Ions from the Calcium and Alkalinity Parts
Adding 1 gallon of each of these additives will result in a residue of ions remaining after calcification. These are mostly sodium and chloride, and the amounts of those two added are equal in numbers (i.e., moles), but slightly different in weight-based concentrations such as ppm because they do not weigh the same.
After adding 594 grams of baking soda (1 gallon of Recipe #1), we will have added 163 grams of sodium. In natural seawater, magnesium is present at about 12.0% of the sodium concentration (by weight). In order to match the magnesium additions to the sodium additions to leave them in a natural ratio, we need to add 12% of 163 grams, or 19.5 grams, of magnesium for every gallon of the two-part additive that we add.
Additionally, we may want to account for magnesium that is actually incorporated into the coral skeletons. For this calculation, I have assumed that the amount of magnesium incorporated is about 6.5% of the calcium level (by weight), or about 2.5% of the skeleton by weight. In the course of adding this gallon of both parts of the two part supplement, we added 141 grams of calcium, so we need to add 0.065 x 141 = 9 grams of magnesium to account for this deposition.
The magnesium parts of the recipe are designed to add enough magnesium so that it is not depleted by either of the two means described above. Because the magnesium supplement (either version) is 47,000 mg/L in magnesium, we need to add (9 +19.5) grams/47 g/L = 610 ml of the magnesium solution for each gallon of the other parts of Recipe #1.
cb684:
These added sodium and chloride ions will with time increase the salinity of the tank. As we add RODI water and do water changes, we adjust the salinity and end up diluting sodium, chloride and magnesium. As time passes, that and consumption will cause magnesium concentration in the water to decrease. When it decreases you add more. That is why IMO it does not make sense to add magnesium if concentration is adequate.
The rate one would need to add magnesium would be about what you said in your post in a tank where there were no other sources of magnesium. But that is not completely true for many tanks because during water changes part of the water with inadequate proportion of sodium, chloride and magnesium is exported, and water with adequate magnesium concentration (sometimes on the upper range) is added correcting its depletion. So if salinity is between 1.025 and 1.026, and magnesium is 1200 - 1400 the proportion between sodium, chloride, and magnesium is correct in spite of the amount of sodium carbonate and calcium chloride added.
@Nowell
@reefwiser
