Marine Aquarium Water Quality
Target Values

Proper technique means accurate, reproducible test results.  The best test kit will give you bad information if you do not use it correctly, or if your technique is sloppy.   Here are some tips for proper testing.

• Read the instructions carefully, and make sure you have all your equipment handy before you begin.
• Use a timer when a test specified a certain waiting period.
• Wash test tubes and other equipment carefully, rinse in distilled water and drain dry after each use.
• Rise test vials and pipettes with the water to be tested immediately prior to carrying out the test.
• For very accurate results, perform the test in triplicate, and average the readings.
• Parts per million (ppm) and milligrams per liter (mg/l) are the same thing, for practical purposes.  To be completely technical, multiply mg/l times specific gravity, to obtain ppm.
• Don't go to all the trouble to buy test kits, learn good techniques, and make regular tests unless you are also going to write down the results in a notebook, for future reference.

pH:  The most   accurate way to test pH is to use an electronic meter, properly calibrated.   Meters should be calibrated prior to each use.  To calibrate, follow the manufacturer's instructions, using pH 7.0 buffer and pH 10.0 buffer as standards.

Alkalinity: This is a measurement of the resistance of the water to a change in pH as acid is added.  It is not the same as pH.  There are many ways to express alkalinity.  Conversions:  1.0 meq/l = 2.8 dKH = 50 ppm CaCO₃.   German degrees of hardness (KH) are often mentioned in aquarium literature, while your local water company probably uses ppm CaCO₃.  Chemists generally use meq/l, which stand for "milliequivalents per liter."

Nitrate:  Nitrate test kits may measure either nitrate nitrogen (NO₃ -N) or nitrate ion (NO₃-).   It is important to know which one your kit tests for.  Nitrate nitrogen readings are multiplied by 4.4 to convert to nitrate ion readings.

Calcium: Calcium concentration is affected by alkalinity. You should test for both at the same time.  Use limewater, a saturated solution of calcium hydroxide (CaOH₂), or a solution of calcium chloride CaC1₂) to maintain the concentration of calcium around 400 mg/l.

Dissolved Gases:   Aquarists do not often experience problems with either dissolved oxygen or carbon dioxide, but there are some circumstances in which tests for these should be performed.

Iron:   Iron is important to hobbyists interested in cultivating macroalgae.