Thanks Randy, I sure would like to see that data to see what type of levels these supplements are designed to maintain. I will have results soon as to what they provide on a pure water sample.
Two parts provide about 18-20 ppm calcium for each 1 meq/L (2.8 dKH) of alkalinity. Calcium carbonate is 20 ppm per 1 meq/L, but some magnesium gets into the structure in place of calcium, so the calcium demand is a tad lower. They also need to provide things like potassium, sulfate, chloride, bromide, etc. at a specific ratio, not because any of those are necessarily consumed, but to maintain them when there is no demand.
I discuss such issues in detail here:
An Improved Do-it-Yourself Two-Part Calcium and Alkalinity Supplement System by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2006-02/rhf/index.php
from it:
Calculation Rationale for the Recipes
The calculation rationale that follows is for Recipe #1. The rationale for Recipe #2 is the same, except that everything is divided by 2 and baking the baking soda is not required. This section is provided for those who want to know how the recipe is devised, who are concerned that there might be an error or who might want to change it slightly. It is not necessary to read the following section if all you want to do is use it.
website, it has a bulk density of 0.82 - 0.96 g/dry mL or 194 - 227 grams/level measuring cup. We will assume that it is 78.5% calcium chloride by weight and weighs 200 grams per level measuring cup. Because calcium comprises 36% of calcium chloride, by weight, each cup contains 200 x 0.785 x 0.36 = 56.5 grams of calcium.
Consequently, dissolving 2 ½ cups (500 g) of Dowflake per gallon = 141 grams of calcium per gallon, or 37,300 mg/L. The final concentration will vary with how much moisture was actually in the calcium chloride, and how well it packed in your measuring cup. A concentration of 37,300 ppm calcium is equivalent to 0.93 molar.
When calcification takes place, two moles of alkalinity are lost for every one mole of calcium. So, we need to match the calcium above with 1.86 molar baking soda (sodium bicarbonate) equivalents (before or after baking, the baking doesn't change the alkalinity). As I measure it, Arm & Hammer baking soda weighs about 264 grams per level measuring cup. Because sodium bicarbonate has a molecular weight of 84 g/mole, we need to dissolve 1.86 x 84 = 156 grams/L, or about 594 grams (2 ¼ level measuring cups) of baking soda per gallon. Note that it doesn't matter how many grams the 594 grams of baking soda becomes after baking. All baking does is change the amount of carbon dioxide and water in the baking soda:
2 NaHCO3 à Na2CO3 + H2O + CO2
More, or less, baking will only alter the pH increase upon addition to the aquarium. However, substantial under-baking may make it impossible to fully dissolve the solid material in the recipe, as sodium bicarbonate is less soluble than sodium carbonate (which is why Recipe #2 is more dilute). Overbaking with respect to time or temperature has no negative effect.
potassium present as an impurity in the Dowflake works to our advantage in this use. Recipe #1 has 1,342 ppm potassium in its calcium part. That amount puts it in the right ratio relative to other ions in the recipe (chloride, sodium, etc.) so that it is neither boosted nor depleted significantly over time based on salinity changes (see modeling below).
Residue Remaining from Recipe #1 when using Recipe #1, Part 3A
After one year of adding 8 ppm of calcium and the accompanying 0.4 meq/L (1.1 dKH) of alkalinity per day (41 mL of both parts per day or 4 gallons of both parts per year in a 50-gallon aquarium, including the effect of the magnesium part #3A, 2440 mL/year), the following residue (Table 2) would remain after calcification and adjustment for salinity (there is roughly a 32% rise in salinity over a year using this addition rate without water changes).
Note that in this recipe, all of the ions match NSW fairly closely (green), but without using Part 3A, the magnesium and sulfate are severely depleted (red).
Residue Remaining from Recipe #1 when using Recipe #1, Part 3B
After one year of adding 8 ppm of calcium and the accompanying 0.4 meq/L (1.1 dKH) of alkalinity per day (41 mL of both parts per day or 4 gallons of both parts per year in a 50-gallon aquarium, including the effect of the magnesium sulfate solution, 2440 mL/year), the following residue (Table 3) would remain after calcification and adjustment for salinity (there is roughly a 29% rise in salinity over a year using this addition rate without water changes):
Note that in this recipe, all of the ions except sulfate (red) match NSW fairly closely (green), but without using Part 3A, magnesium and sulfate are severely depleted (red).
In a previous article discussing
water changes, I showed how the rise in sulfate shown in Table 2 is mitigated to some extent by water changes. Those data are reproduced in Figure 5 below, which shows the effect of daily water changes amounting to 7.5%, 15% and 30% on a monthly basis. Clearly, the 15% and 30% changes per month mitigate the rise in sulfate over a year by a substantial amount (reducing the increase by 54% and 74%, respectively).
