How to Test Aquarium Salinity

In the marine aquarium the level of salinity will greatly affect the overall health of the fish and corals. The best salinity level for marine fish is 1.018 degrees of specific gravity; for corals it is 1.023-1.024. There are a variety of test devices; choose the one that best suits your needs and your budget.

Difficulty: Easy

Instructions

Things You'll Need:

• a hydrometer or refractometer
• small water sample from the aquarium
• small water dropper
• good lighting

1. If you are using a hydrometer that floats in water, place it in the area of lowest water flow and wait until it comes to rest in order to get the reading. Where the surface of the water meets the mark on the meter is the salinity level of your aquarium. If your hydrometer has a "green" zone, it should be within this zone.

2. If your hydrometer has a needle and must be filled with water, dunk it into your aquarium. Either hold it steady or place it on a level surface to allow the needle to stablize. The mark at which the needle points is the salinity level of your aquarium.

3. If you use a refractometer you must put a few drops of aquarium water on the glass face and hold it under a bright light. Turn the eyepiece to bring the view into focus. Where the white line crosses the mark is the salinity level of your aquarium. This is by far the most accurate method.

Tips & Warnings

• Your salinity level will naturally rise as the water slowly evaporates from your aquarium. To return it to normal simply add FRESH (no salt) water.
• Most hydrometers are inaccurate, some by up to 2 or more degrees. Have your local aquarium fish store calibrate your hydrometer by comparing it to a refractometer.
• Any refractometer must be calibrated to maintain accuracy. There should be a small screw near the glass face. For most models, simply place a few drops of Reverse Osmosis or Distilled water on the glass face, and use a jewelry screwdriver to turn the screw until the reading is exactly at "zero".