pH, Calcium Alkalinity and Magnesium Explained

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 Sodium Carbonate 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 disproportionably 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

Balanced Calcium and Alkalinity Ratios
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
Magnesium levels should be maintained around 1350 ppm.
**Magnesium increases as salinity levels increases.

Correcting Imbalances

There are four main problems that can exist:

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. 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. If the problem is not easily corrected, test your magnesium. If your magnesium readings are below 1200ppm, dose magnesium accordingly.