An Improved Do-it-Yourself Two-Part
Calcium and Alkalinity Supplement System


In a previous article I showed how to make your own inexpensive two-part calcium and alkalinity supplement system. The only materials required are calcium chloride (available in bulk as a deicer for pools, for cement making and even for weighing down tractor tires), baking soda (from a grocery store) and Epsom Salts (which are inexpensive and available at most drug stores). Recently, however, some aquarists have found good quality bulk sources of magnesium chloride (sold as a deicer by the Dead Sea Works company). Using magnesium chloride improves the recipe and eliminates a primary concern with the previous recipe: the potential buildup of sulfate over time.

This article provides an improved recipe for the two-part additive using magnesium chloride. This improved recipe does not substantially skew the aquarium's ionic balance. This article also provides the original recipe for folks who cannot find, or choose to not use, magnesium chloride. The buildup of sulfate over time when using the original recipe is shown graphically under different water change scenarios.

The sections are:

Introduction


This two-part additive system is similar to the many commercial two-part additive systems. It allows aquarists to supplement calcium and alkalinity without greatly skewing the water's ionic balance (something that is claimed by many of the commercial products, but that is not independently verified). Equal addition of the two parts to a reef aquarium will provide calcium and alkalinity in approximately the same ratio used in calcification by corals and coralline algae.

One part is calcium chloride dissolved in water, and the other part is baking soda (either baked or not prior to use) dissolved in water. The balance between these two additives is very important, and the recipe is designed for aquarists to dose equal portions of the two parts every time they dose. An aquarium using such a balanced additive system is unlikely to undergo large short-term swings in calcium and alkalinity, as can happen if an aquarist using independent additives were to inadvertently overdose one or the other. This problem is surprisingly common, and using balanced calcium and alkalinity additive systems for most additions serves to eliminate that potential danger.

A "third" part of this additive system contains magnesium, sulfate, and chloride. It needs to be added only once in a while at a fixed rate relative to the other two parts. It cannot be readily combined with either of the other parts, based on the ingredients discussed here that are readily available to aquarists (commercial systems may have more chemicals to select from, such as sodium sulfate, allowing more flexibility). This third part is necessary to prevent magnesium depletion, and to prevent abnormal chloride and sulfate ratios in the aquarium.

The seven most abundant ions in seawater, in decreasing order of concentration, are chloride, sodium, sulfate, magnesium, calcium, potassium and bicarbonate. Using this new recipe will keep all of these ions in their appropriate ratios (detailed below).

Comparing the Two Primary Recipes


This article actually details two primary recipes. One uses raw baking soda, and the other uses baking soda that aquarists bake before use. The baking drives some of the carbon dioxide out of the baking soda, and raises its pH as well as its alkalinity. Be careful about substituting other brands for the Dowflake and the magnesium chloride sold by the Dead Sea Works company. A later section in this article details substitution issues.

Recipe #1 is for use in reef aquaria whose pH is normal to low. In practice, more reef aquarists end up choosing this recipe than Recipe #2. It will tend to raise pH due to its alkalinity part's elevated pH, as do most of the commercial two-part additives. The increase in pH depends on the aquarium's alkalinity and, of course, on how much is added. Adding on the order of 0.5 meq/L of alkalinity increases the pH by about 0.3 pH units immediately upon its addition (and even higher, locally, before it has a chance to mix throughout the aquarium).

If you are using limewater (kalkwasser) and the aquarium is at pH 8.4 or above, this recipe is not the best choice. Otherwise, it is likely to be a good option. It is twice as concentrated as Recipe #2, because the baking process makes the baking soda more soluble.

Recipe #2 is for use in reef aquaria whose pH is on the high side (above 8.3 or so). It will have a very small pH lowering effect when initially added. The pH drop achieved will depend on the aquarium's alkalinity and, of course, on how much is added. Adding on the order of 0.5 meq/L of alkalinity drops the pH by about 0.04 pH units immediately upon its addition.

If you are using limewater (kalkwasser) and the aquarium is at pH 8.4 or above, this recipe may be the best choice. It is half as concentrated as Recipe #1 because the raw baking soda is less soluble because it's unbaked.

Recipe #1


In this recipe three stock solutions are made. Two are used frequently, and one is used only occasionally to balance other elements not added in the first two. The solutions can be mixed and stored in any plastic or glass container, and they will last indefinitely. Plastic 1-gallon milk jugs (typically made of HDPE, high density polyethylene) can be a good storage choice.

Recipe # 1, Part 1: The Calcium Part

Dissolve 500 grams (about 2 ½ cups) of calcium chloride dihydrate (such as Dowflake 77-80% calcium chloride or ESV calcium chloride; see below for substitutes and sources) in enough water to make 1 gallon of total volume. You can dissolve it in about ½ gallon of water, and then pour that into the 1 gallon container and fill it to the top with more freshwater. This solution has about 37,000 ppm calcium.

Figure 1. A bag of Dowflake obtained at a Home Depot store
in the Boston area. Photo by Moe Kirby.

If you use an anhydrous or monohydrate calcium chloride (such as Dow Mini-Pellets, Kent's Turbo Calcium, Prestone Driveway Heat or Peladow Calcium Chloride), then you should use about 20% (1/5) less solid calcium chloride by volume to make the recipe. Note that the solution will get quite hot when dissolving anhydrous calcium chloride. See the section on substitutions for further information.

Figure 2. A container of Peladow obtained at a supply store
in the Boston area (Amesbury Industrial Supply).
Photo by Patrick Higgins.

Recipe #1, Part 2: The Alkalinity Part

Spread baking soda (594 grams or about 2 ¼ cups) on a baking tray and heat in an ordinary oven at 300°F for one hour to drive off water and carbon dioxide. Overheating is not a problem, either with higher temperatures or longer times. Dissolve the residual solid in enough water to make 1 gallon total. This dissolution may require a fair amount of mixing. Warming it speeds dissolution. This solution will contain about 1,900 meq/L of alkalinity (5,300 dKH). I prefer to use baked baking soda rather than washing soda in this recipe as baking soda from a grocery store is always food grade, while washing soda may not have the same purity requirements. Arm & Hammer brand is a fine choice. Be sure to NOT use baking powder. Baking powder is a different material that often has phosphate as a main ingredient.

Once these two solutions are created, they can be added as frequently as necessary to maintain calcium and alkalinity. For further dosing instructions, see below.

Recipe #1, Part 3: The Magnesium Portion

The magnesium portion gives us two options, with Part 3A being preferred from an aquarium chemistry standpoint. Pick one and follow the same dosing directions regardless of which version you select.

Recipe #1, Part 3A

Dissolve Epsom salts (3 cups) and magnesium chloride hexahydrate sold by the Dead Sea Works company (5 cups) in enough purified freshwater to make 1 gallon total volume. There will likely be a precipitate that forms even if you fully dissolve both ingredients separately. That precipitate is calcium sulfate (calcium as an impurity in the magnesium chloride and sulfate from the Epsom salts). It is fine and appropriate to dose the precipitate along with the remainder of the fluid by shaking it up before dosing.

This solution is added much less frequently than the other two parts. Each time you finish adding a gallon of both parts of Recipe #1, add 610 mL (2 ½ cups) of this stock solution. You can add it all at once or over time as you choose, depending on the aquarium's size and set up. Add it to a high flow area, preferably a sump. In a very small aquarium, or one without a sump, I suggest adding it slowly.

The first time it's added, I recommend adding just a small portion and making sure there isn't any problem (such as corals closing up due to stress) before adding the remainder. Make sure corals and other organisms don't get blasted with locally high concentrations of the main ingredients or impurities, or else they may become stressed. This solution contains about 47,000 ppm magnesium, 70,000 ppm sulfate and 86,000 ppm chloride.

Recipe #1, Part 3B

Dissolve a 64-ounce container of Epsom salts (about 8 cups) in enough purified freshwater to make 1 gallon total volume. This solution is added much less frequently than the other two parts. Each time you finish adding a gallon of both parts of Recipe #1, add 610 mL (2 ½ cups) of this stock solution. It can be added all at once or over time as you choose, depending on the aquarium's size and set up. Add it to a high flow area, preferably a sump. In a very small aquarium, or one without a sump, I suggest adding it slowly.

The first time it's added, I recommend adding just a small portion and making sure there isn't any problem (such as corals closing up due to stress) before adding the remainder. Make sure corals and other organisms don't get blasted with locally high concentrations of the main ingredients or impurities, or else they may become stressed. This solution contains about 47,000 ppm magnesium and 187,000 ppm sulfate.

Recipe #2


In this recipe three stock solutions are created. Two are used frequently, and one is used only occasionally to balance other elements not added in the first two. The solutions can be mixed and stored in any plastic or glass container. Plastic 1-gallon milk cartons (typically made of HDPE, high density polyethylene) can be a good storage choice.

Recipe #2, Part 1: The Calcium Part

Dissolve 250 grams (about 1 ¼ cups) of calcium chloride dihydrate (such as Dowflake 77-80% calcium chloride or ESV calcium chloride; see below for substitutes and sources) in enough water to make 1 gallon of total volume. You can dissolve it in about ½ gallon of water, and then pour that into the 1 gallon container and fill it to the top with more freshwater. This solution is about 18,500 ppm in calcium.

If using an anhydrous or monohydrate calcium chloride (such as Dow Mini-Pellets, Kent's Turbo Calcium, Prestone Driveway Heat or Peladow Calcium Chloride), then about 20% (1/5) less solid calcium chloride by volume should be used to make the recipe. Note that the solution will get quite hot when dissolving anhydrous calcium chloride. See the section on substitutions for further information.

Recipe #2, Part 2: The Alkalinity Part

Dissolve 297 grams of baking soda (about 1 1/8 cups) in enough water to make 1 gallon total. This dissolution may require a fair amount of mixing. Warming it speeds dissolution. This solution will contain about 950 meq/L of alkalinity (2660 dKH). As mentioned earlier, Arm & Hammer is a fine brand of baking soda to use in these recipes. Be sure to NOT use baking powder. Baking powder is a different material that often has phosphate as a main ingredient.

Once these two solutions are created, they can be added as frequently as necessary to maintain calcium and alkalinity. For further dosing instructions, see below.

Recipe #2, Part 3: The Magnesium Portion

The magnesium portion again gives us two options, with Part 3A being preferred from an aquarium chemistry standpoint. Pick one and follow the same dosing directions regardless of which version you select.

Recipe #2, Part 3A

Dissolve Epsom salts (3 cups) and magnesium chloride hexahydrate (5 cups) in enough purified freshwater to make 1 gallon total volume. There will likely be a precipitate that forms even if you fully dissolve both ingredients separately. That precipitate is calcium sulfate (calcium as an impurity in the magnesium chloride and sulfate from the Epsom salts). It is fine and appropriate to dose the precipitate along with the remainder of the fluid by shaking it up before dosing.

This solution is added much less frequently than the other two parts. Each time you finish adding a gallon of both parts of Recipe #2, add 305 mL (1 ¼ cups) of this stock solution. You can add it all at once or over time as you choose, depending on the aquarium's size and set up. Add it to a high flow area, preferably a sump. In a very small aquarium, or one without a sump, I suggest adding it slowly.

The first time it's added, I recommend adding just a small portion and making sure there isn't any problem (such as corals closing up due to stress) before adding the remainder. Make sure corals and other organisms don't get blasted with locally high concentrations of the main ingredients or impurities, or else they may become stressed. This solution contains about 47,000 ppm magnesium, 70,000 ppm sulfate and 86,000 ppm chloride.

Recipe #2, Part 3B

Dissolve a 64-ounce container of Epsom salts (about 8 cups) in enough purified fresh water to make 1 gallon total volume. This solution is added much less frequently than the other two parts. Each time you finish adding a gallon of both parts of Recipe #2, add 305 mL (1 ¼ cups) of this stock solution. You can add it all at once or over time as you choose, depending on the aquarium's size and set up. Add it to a high flow area, preferably a sump. In a very small aquarium, or one without a sump, I suggest adding it slowly.

The first time it's added, I recommend adding just a small portion and making sure there isn't any problem (such as corals closing up due to stress) before adding the remainder. Make sure corals and other organisms don't get blasted with locally high concentrations of the main ingredients or impurities, or else they may become stressed. This solution contains about 47,000 ppm magnesium and 187,000 ppm sulfate.

Dosing Instructions


The dosing instructions are basically the same for each recipe, although any given aquarium will end up using about twice as much of recipe #2 as recipe #1 to add the same amount of calcium and alkalinity.

To initiate dosing, first adjust calcium and alkalinity to roughly their correct ranges. This may require a substantial dose of just the calcium part if calcium is low (e.g., below 380 ppm). I would suggest targeting calcium between 380 and 450 ppm, and alkalinity between 2.5 and 4 meq/L (7-11 dKH; 125-200 ppm calcium carbonate equivalents).

This calculator shows how much of what parts to add in order to boost one or both of the parameters by a certain amount:
Reef chemicals calculator
http://home.comcast.net/~jdieck1/chem_calc3.html

Then, once things seem roughly correct, select a starting daily dose for routine dosing. Here are some suggested starting doses, but the exact values do not matter much. The suggested doses apply to both recipes.

Table 1. Suggested starting daily doses of this supplement in different aquaria.
Tank Description:
Suggested Starting Doses:
 
Recipe #1
Recipe #2
Fish-only with live rock
0.1 mL/gallon
0.2 mL/gallon
New tank, few corals
0.2 mL/gallon
0.4 mL/gallon
Low demand
0.3 mL/gallon
0.6 mL/gallon
Mixed tank
0.5 mL/gallon
1 mL/gallon
Heavy demand (SPS corals)
1 mL/gallon
2 mL/gallon

After a few days of dosing, note whether alkalinity is low, high or on target. Only bother to test alkalinity, not calcium, during this period, because it is much more sensitive than calcium to over- or underdosing. Adjust the dose up or down as necessary to increase or decrease the alkalinity.

Once you have determined the proper dose, continue it until there is a substantial reason to adjust it (such as falling alkalinity as the corals increase in size). When adjusting the dose, raise or lower both of the recipe's parts together.

Resist the temptation to keep jiggering calcium and alkalinity independently. They will need occasional corrections, but that should not be the normal course of dosing unless there are substantial outside influences, such as water changes with a salt mix that does not match the tank's parameters or an error in making the mixes.

Check alkalinity fairly frequently to make sure the dosing continues at a suitable rate. Check it maybe once a week to once a month (or less as you get more experienced with the system and the tank). Check calcium once a month to once every few months to make sure it continues on track.

Remember to add an appropriate amount of Part 3 each time you finish adding a gallon of Parts 1 and 2.

Substitutes for Dowflake Calcium Chloride


If Dowflake calcium chloride or a repackaged version (such as All-Clear) cannot be located, Peladow or Dow Mini-Pellets, which are dehydrated versions of Dowflake (that is, they have less water in the crystals), can be substituted. In addition to the Peladow brand name, Peladow also is sold as Prestone Driveway Heat and possibly as some other common brands. Kent Turbo Calcium is also suitable and is an anhydrous calcium chloride. Any FCC (food), USP (pharmaceutical) or BP (pharmaceutical) grades of calcium chloride should be suitable.

Peladow, Dow mini-Pellets, Prestone Driveway Heat, Kent Turbo Calcium and other dehydrated calcium chloride products are more potent than Dowflake. The dehydration makes them both more potent by weight, and more dense, so they are much more potent by volume. The problem is that it is rarely clear how much moisture they contain. Peladow specifies 90% calcium chloride minimum, but it may be higher in some cases. Dow Mini-Pellets say 94% minimum, but it actually has a lower bulk density than Peladow. The best guess for an amount to use is based on the hydration levels and bulk density provided by Dow for these products. Using these numbers, I suggest that aquarists use 20% less VOLUME of the dehydrated versions in the recipes than the Dowflake they call for. So a recipe calling for 5 cups of Dowflake would use 4 cups of Peladow, Prestone Driveway Heat, Kent Turbo Calcium, etc.

Choosing other unknown brands of any of the products may be fine, or not. I've not tested them for purity.

Substitutes for Dead Sea Works Magnesium Chloride Hexahydrate


Dead Sea Works is a business unit of ICL Fertilizers. They sell magnesium chloride hexahydrate in the U.S. as a deicer and apparently distribute it also to artificial seawater (salt) manufacturers. In the past, potential impurities (such as ammonia) have left many aquarists, and even some companies, wary of using deicing or any other grades of magnesium chloride hexahydrate. However, the Dead Sea Works company recently supplied a detailed impurity profile of its product listing most impurities (29 in all). None was high enough to concern reef aquarists. Included in the profile was an indication that it had adequately low ammonia. Subsequent analysis by Greg Hiller of some of the supplied material confirmed that the ammonia is low enough to use.

The recipe above is based on the MAG Flake's bulk density supplied by the manufacturer. They also sell a pelletized product, which may be OK to use, but probably has a slightly different bulk density (they do not provide the bulk density for that to my knowledge). Exact values for the magnesium part are less important than for the other parts, and when using pellets I recommend just following the directions stated here for flakes, unless better information becomes available in the future.

Editors note (3/10/07): Note, the manufacturer of MAG flake has alerted us that they very strongly recommend against using this product in reef aquaria.  While many reef aquarists have successfully used the product, the manufacturer does not claim to be able to provide this product at suitable quality in the future.


Figure 3. One style of bag of magnesium chloride hexahydrate
made by the Dead Sea Works and sold at a supply store in the Boston
area (Amesbury Industrial Supply). I also saw such a bag at my local
Home Depot. Photo by Patrick Higgins.

At this time magnesium chloride hexahydrate from the Dead Sea Works is the only such product that I recommend, but others may be acceptable. Choosing other unknown brands may be fine, or not. I've not tested them for purity.

Where to Buy the Materials


Baking soda (sodium bicarbonate) is best obtained from a grocery store to ensure that it is a food grade material. Arm & Hammer is a fine brand, as is a store brand. Be sure to NOT use baking powder. Baking powder is a different material that often has phosphate as a main ingredient.

Calcium chloride dihydrate (Dowflake) can often be obtained at stores such as Home Depot as a deicer. All-Clear calcium chloride for pools is repackaged Dowflake.

The following links lead to companies that are believed to supply Dowflake. Some will ship and some may be available only via local pickup:
http://www.buckeyefieldsupply.com/showproducts...&showspecials=124
http://www.flordrisupply.com/index2.html
http://www.mainstreetseedandsupply.com/saltproducts.htm
http://www.gemplers.com/a/shop/product.asp...=21BR001
http://www.meltsnow.com/products-dry-calcium-chloride.htm
http://www.cal-chlor.com/products.htm
http://www.farrellequipment.com/catalog/ChemicalCementitious.pdf

Peladow is available from some of the suppliers above and is sold at many home products stores as Prestone Driveway Heat for deicing.

Magnesium chloride hexahydrate made by the Dead Sea Works is sold at many home stores, including Home Depot, often labeled as MAG Flake. It may be repackaged as Meltsnow:
http://www.meltsnow.com/msds-mag-flakes.htm

It may also be available from these stores:
http://www.harveysalt.com/prod01.htm
http://www.meltsnow.com/products-dry-magnesium-chloride.htm

Figure 4. A second style of bag of magnesium chloride hexahydrate
made by the Dead Sea Works. This packaging was obtained in a group
buy organized by the Boston Reefers. Photo by Greg Thevenin.

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.

The Design of the Calcium and Alkalinity Parts

The Dowflake material is supposed to contain 77-80% calcium chloride. From the Dow Flake 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    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.

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.

Interestingly, the 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).

Table 2. Elements present after one year of additions and after adjusting for salinity changes. Calculations assume no water changes take place.
Element
Seawater Concentration
Final Tank Concentration (w/ Part 3A)
Final Tank Concentration (w/o Part 3)
Chloride
19,350
19,440
19,710
Sodium
10,760
10,730
11,360
Sulfate
2,710
2720
2170
Magnesium
1,290
1270
880
Calcium
420
420 (assumed)
420 (assumed)
Potassium
400
384
405

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).

Table 3. Elements present after one year of additions of Recipe #1, using Part 3B and after adjusting for salinity changes. Calculations assume no water changes take place.
Element
Seawater Concentration
Final Tank Concentration (w/ Part 3B)
Final Tank Concentration (w/o Part 3)
Chloride
19,350
18,470
19,710
Sodium
10,760
10,650
11,360
Sulfate
2,710
3840
2170
Magnesium
1,290
1282
880
Calcium
420
420 (assumed)
420 (assumed)
Potassium
400
387
405

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).

Figure 5. Sulfate concentration as a function of time when performing daily water changes equivalent to 0% (no changes), 7.5%, 15% and 30% of the total volume each month (in other words, 0%, 0.25%, 0.5% and 1% per day). In this example, sulfate starts at a natural level of 2710 ppm, and the model assumes the usage of a moderate amount of calcium chloride and sodium bicarbonate to maintain calcium and alkalinity, and Epsom salts (magnesium sulfate) to maintain magnesium.

Summary


This improved two-part additive system is inexpensive and simple to make. Many reef aquarists have been successfully using the original recipe for more than a year now, and this improvement should make it even more appealing.

For those who use it, be sure to check the calcium and alkalinity values over time, even after establishing a routine that looks to do the job. Because of the uncertainty in the amount of moisture in these products when purchased, and in the amounts that you actually measure out, the system may not be perfectly balanced, and a slow drift toward elevated or depleted calcium (assuming you are dosing to maintain alkalinity) may take place even in the absence of other potentially disrupting factors such as water changes.

Measuring magnesium once in a while is also likely a good move, just in case it is being used more or less rapidly than expected for a typical case.

Happy Reefing!



If you have any questions about this article, please visit my author forum on Reef Central.

Reference Links:


Purity of Calcium Chloride
http://www.advancedaquarist.com/issues/mar2004/chem.htm

A Homemade Two-Part Calcium and Alkalinity Additive System
http://www.advancedaquarist.com/issues/april2004/chem.htm




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An Improved Do-it-Yourself Two-Part Calcium and Alkalinity Supplement System by Randy Holmes-Farley - Reefkeeping.com