Alkalinity is important in saltwater aquariums for a number of reasons. Proper alkalinity (142-215 ppm or 8-12 dKH) is vital for coral calcification and skeletal formation; it prevents pH swings, alkalinity burn, coral bleaching, and tissue loss; and it improves equipment performance. It is best to test for alkalinity weekly, or as needed depending on your dosing schedule, in order to maintain a healthy aquarium. Simply put, the greater the tank's alkalinity, the greater its ability to prevent rapid swings in pH.

What Is Alkalinity?

Total alkalinity is the measurement of all bases in the water and can be thought of as the buffering capacity of water, or its ability to resist change in pH. The most common and important base is carbonate. Total alkalinity is expressed as milligrams per liter (mg/L) or parts per million (ppm) of calcium carbonate (CaCO3). In the aquarium industry, total alkalinity may be referred to as "carbonate hardness" or "KH," which is often measured in degrees (dKH) rather mg/L or ppm. One dKH is equal to 17.9 mg/L or 17.9 ppm.

Why Do We Need to Test Alkalinity? 

Alkalinity is a system’s ability to buffer its pH as acids are introduced. In saltwater systems alkalinity is present in two main forms: carbonate (CO32-) and bicarbonate (HCO3-). It’s important to check for alkalinity in reef aquariums because it’s vital to the calcification of corals and skeletal formation of many marine organisms. The recommended range for alkalinity in reef aquariums is between 142-215ppm or 8-12 dKH. 

There are many solutions and chemicals you can add to a reef tank to increase alkalinity, such as sodium bicarbonate, Kalkwasser (Kalk/limewater) or various commercial premixes. Too high alkalinity can be damaging to organisms in an aquarium and even cause alkalinity burn, coral bleaching, or tissue loss. Additionally, a high alkalinity level puts the tank at risk for calcium carbonate precipitation (limestone formation). This precipitation can sometimes damage equipment and cause heaters or pumps to perform poorly. When the alkalinity drops too low your tank is susceptible to detrimental pH swings, causing organisms that utilize alkalinity to be unable to take in what they need. 

How To Test Alkalinity Using the Hanna Checker

The Hanna Marine Alkalinity (dKH) Checker and Hanna Marine Alkalinity (ppm) Checker are designed to make testing quick and easy.

  1. Press the button to power the meter on. When Add C1 appears on the screen, you are ready to begin testing.
  2. Fill a cleaned cuvette to the 10mL line with sample and fasten the cap.
  3. Using a microfiber cloth, wipe the cuvette to remove any oils or fingerprints from the glass. Then place the cuvette into the checker and close the lid, making sure it is completely closed. It is important to make sure that the lid is completely closed for an accurate reading.
  4. Press the button.
  5. Once the screen shows Add C2, use the syringe to extract 1mL of Hanna Reagent Solution from the reagent bottle. Once the reagent has been added, cap the cuvette and invert five times to mix.
  6. Wipe the cuvette of any oils or fingerprints and place back into the meter.
  7. Press the button, and the meter will display the alkalinity in either degrees Karbonathärte (dKH) or parts per million (ppm), depending on which Checker you’ve purchased.

Still unsure about checking your alkalinity? CLICK HERE to watch our video of reef expert Wayne taking you through step-by-step!