Your saltwater companions need a basic -- as opposed to neutral or acidic -- aquatic environment, and they need it to remain consistent. The pH shouldn't be below 8.0 or above 8.4 for saltwater aquariums, with 8.2 being standard. Test the pH at least once per week.
Buy an electronic pH meter from your trusted aquarium supply retailer. Get one with the capacity to use at least two sample solutions for calibration. Purchase two pH solutions for calibrating the meter, too. They must be outside your marine aquarium's target pH range of 8.0 to 8.4, so 7.0 and 9.0 sample solutions will work.
Review your pH meter's directions thoroughly to ensure no variations occur from standard use. Always defer to the information in your product's manual.
Pour 2 to 3 inches of distilled water into a plastic cup. Dip the pH meter's electrode into the water to rinse. Using distilled helps preserve the accuracy of readings, as its impurities have been removed and so can't affect your meter's electrode. Remove the electrode and blot it dry carefully with a clean paper towel to avoid damage.
Set your pH meter to calibration mode. Pour 3 inches of the lower-pH solution into a new plastic cup. Submerge the electrode 1 to 2 inches as directed. Use the meter's buttons to set this reading at 7.0. Confirm the setting if prompted to.
Remove the electrode and rinse it again with a new cup of distilled water. Gently dab it dry again with a paper towel.
Repeat the calibration process using your other pH solution and confirm the setting at 9.0. Rinse and dry again with a new cup of distilled water and a new paper towel when you're finished calibrating the meter.
Turn on your pH meter again and put it to the appropriate setting for a reading. Submerge the electrode 1 to 2 inches as directed into your aquarium water. Wait for the screen to display your tank water's pH reading.
Finish by rinsing and drying the electrode in the same manner you've already done so. Place the meter back in its packaging and put it in a safe storage location.
Pick up a dropper-bottle home test kit that measures pH and that's labeled for use with saltwater. Read through the instructions before use; though there are standard practices, different products and brands sometimes have slightly different specifications.
Use a clean spoon to put a sample of your tank water into the kit's test tube. Fill the tube to the measurement line indicating a proper sample quantity. Typically, you use 5 milliliters of your aquarium's water.
Unscrew the kit's dropper bottle and use the dropper to add three drops of the pH test solution into your tank water sample in the test tube. Check the product instructions to see whether you must invert your particular dropper bottle to acquire uniform drops.
Affix the test tube's cap and turn the tube over a few times to mix the solution into the tank water sample.
Go to a well-lit area. Compare the water sample color to the color chart that came with your test kit. The color correlates to a specific pH.