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pH, Calcium Alkalinity and Magnesium Explained
The goals of this article are to clearly and simply define pH, Calcium, Alkalinity and Magnesium, describe their relation to one another, demonstrate how to correct imbalances and examine different methods of dosing. For this article, I will reference “The Reef Aquarium - Volume 3,” by Julian Sprung and Charles Delbeek.
Definitions and Relationships
pH is the concentration of hydrogen (H+) to hydroxide (OH-) ions in a solution. pH can range from 0-14 with a pH of 0-6.99 being acidic, a pH of 7 being neutral and a pH of 7.01-14 being basic. pH is based on a logarithmic scale, so a pH of 9 is ten times more basic than a pH of 8 and a pH of 10 is one hundred times more basic than a pH of 8. pH generally varies from 7.9-8.4 in a saltwater aquarium.
**pH increases as oxygen levels increase.
**pH decreases as carbon dioxide levels increase.
**Some Calcium and Alkalinity additives like Kalkwasser increase pH.
**Some Alkalinity additives, like Soda Ash increase pH.
**Some Alkalinity additives, like Sodium Bicarbonate lower pH.
**pH increases cause calcium levels to decrease.
Calcium is one element that calcifying organisms like corals and clams require to grow. Calcium should be maintained at 400-450 mg/L. When calcium falls below 360 mg/L it may cause a decrease in coral growth (p. 203). If calcium rises disproportionally to alkalinity via dosing, it can cause a sudden drop in alkalinity and cause the calcium to precipitate into the water, creating a snow flake effect.
**Calcium increases as salinity levels increase.
**When Calcium increases as Alkalinity slightly decreases.
**Calcium and Alkalinity should be dosed in equal parts as corals require equal parts of each to grow.
Alkalinity is seawater’s ability to buffer the pH lowering effect of acids through carbonates and bicarbonates. Alkalinity is measured in two methods, meq/L and dKH. dkH can be determined by taking meq/L x 2.8. For example 2 meq/L = 5.6 dKH. Alkalinity should be maintained at 9-13 dKH.
**When Alkalinity increases Calcium slightly decreases.
The precipitation of calcium carbonate consumes its two components (calcium and alkalinity) in an exact 1:1 ratio. This corresponds to one meq/L (2.8 dKH) for every 20 ppm of calcium (p. 206).
Balanced Calcium and Alkalinity Ratios (p.207):
1.4 dKH to 350 ppm
2.1 dKH to 375 ppm
5.6 dKH to 400 ppm
9.1 dKH to 425 ppm
12.6 dKH to 450 ppm
16.1 dKH to 475 ppm
Magnesium has two important effects on saltwater reef aquariums. Magnesium increases the buffering capacity of saltwater against the pH lowering effect and reduces the rate of calcium precipitation. As a result it is easier to maintain and balance higher levels of calcium and alkalinity (p. 174). Magnesium levels should be maintained around 1350 ppm.
**Magnesium increases as salinity levels increases.
Correcting Imbalances
Quality Test Kits are absolutely critical. Without accurate readings you may have problems, but not know it, or everything may be fine, but the test kits show faulty results. Discovery Aquatics recommends using ELOS, Salifert (with exception to their alkalinity, tendency to give extreme false highs), LaMotte, Merck and Tropic Marin.
There are four main problems that can exist:
1. Both Calcium and Alkalinity are too high.
2. Both Calcium and Alkalinity are too low.
3. Calcium is too high relative to Alkalinity.
4. Alkalinity is too high relative to Calcium.
1. Both Calcium and Alkalinity are too high. If both calcium and alkalinity are balanced, the problem should correct itself overtime as calcium and alkalinity are used up equally.
2. Both Calcium and Alkalinity are too low. If both calcium and alkalinity are balanced, you need to add equal portions of a calcium and alkalinity supplement, like B-Ionic. If the problem is not easily corrected, test your magnesium. If your magnesium readings are below 1200ppm, dose magnesium accordingly.
3. Calcium is too high relative to Alkalinity. Your calcium to alkalinity ratio is unbalanced; you need to increase your alkalinity supplement. Do not add kalkwasser or other calcium balanced additives, as this will only continue to raise calcium. Instead, only dose alkalinity or the alkalinity portion of a two part supplement, like B-Ionic. If the problem is not easily corrected, test your magnesium. If your magnesium readings are below 1200ppm, dose magnesium accordingly.
4. Alkalinity is too high relative to Calcium. Your calcium to alkalinity ratio is unbalanced; you need to increase your calcium supplement. Do not add kalkwasser or other calcium balanced additives, as this will only continue to raise alkalinity. Instead, only dose calcium or the calcium portion of a two part supplement, like B-Ionic. If the problem is not easily corrected, test your magnesium. If your magnesium readings are below 1200ppm, dose magnesium accordingly.
Dosing Methods
Kalkwasser powder contains an equal portion of calcium and alkalinity. Kalkwasser is best used in aquariums with low to medium calcium demand, or in combination with another calcium supplement. Kalkwasser is made by mixing 2 tablespoons of powder per gallon of fresh water. Then use the kalkwasser mix as part of your evaporation top of water in combination with fresh RODI water. The biggest disadvantage of kalkwasser is it can be messy to make and can create pH spikes if overdosed. Avoid pH spikes by monitoring your pH as kalkwasser. Kalkwasser can also be used to eliminate aiptasia. The most readily available brand of kalkwasser is Kent Marine.
Two-Part supplements usually contain a bottle of calcium and a bottle of alkalinity. These supplements are added daily in equal portions to the aquarium to create an ionic balance. The system is best used in aquariums with medium calcium demand. The major advantage to two-part is that calcium and alkalinity imbalances can be corrected without purchasing any additional supplements. The disadvantage is that it requires daily dosing to the aquariums, (to solve this problem aquarists have purchased peristaltic dosing pumps and digital timers to automate and control dosing). There are many two-part supplements available, we prefer to use ESV B-Ionic and tend to avoid Kent Marine Liquid Calcium and Alkalinity.
Calcium Reactors are for aquariums with high calcium demand, usually large SPS Coral systems. Calcium reactors use CO2 to breakdown calcium media, which then releases an equal part of calcium and alkalinity into the water. Once dialed in, a calcium reactor can go several months without the addition of media, but it should be monitored closely. The setup can be costly as you will need a calcium reactor, calcium media, CO2 tank, solenoid, bubble counter, CO2 safe tubing and a pH monitor and controller. An aquarium running a calcium reactor must have a pH monitor and controller because the effluent of the reactor is CO2 saturated, which means it has a low pH. If the pH drops below 8.X then the pH monitor should send a signal to the controller to turn off the CO2 injector. Note: A calcium reactor is tuned into to the aquarium’s alkalinity, not its calcium level.