I get plenty of messages asking about salinity in the reef tank or saltwater fish only tank. Below we address some of these questions.

What is the recommended specific gravity/salinity for a saltwater fish or reef tank?

Reef tanks should be kept between 1.023 and 1.027 to keep coral and inverts happy.

However, if you have a fish only saltwater system (with no invertebrates) you may consider keeping the salinity slightly lower – down to 1.018 to help prevent outbreaks of ich.

How do you keep the correct salinity (salt level/specific gravity)?

The most important part about keeping your salinity at the right level is having the right equipment to measure it.  Salinity can be measured best with a refractometer which can be purchased at your Local Fish Store. Refractometers are moderately expensive, so many people might opt for a simple hydrometer.

The key to keeping salinity stable is to remember that salt does not evaporate. When freshwater evaporates from a saltwater aquarium, the ratio of salt increases because there is less water left to dilute it.  When you add fresh water to your saltwater aquarium to make up for evaporation, the salt level decreases because there is more water to dilute the salt.  This means only add freshwater to replace evaporated water.

Likewise, if you remove water manually from your aquarium with a hose or a cup when doing a water change or acclimating fish, the salt goes with the water.  Since you are removing both salt and water, you should add back saltwater to replace the water you took out.  Remember that salt should be mixed with RO/DI water before it is added to the aquarium.

I’m a busy person. Isn’t there an easier way to deal with mixing saltwater?

As a matter of fact, there is!  Many fish stores sell pre-mixed saltwater that is mixed to reef specifications, or 1.023.  You may bring your own container or purchase one at the store.  Containers should be clean and not used for any other purpose other than carrying water intended for your aquarium.

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