What is the difference between salinity and specify gravity (s.g.)?
• Salinity is measured in ppt.
• Specific gravity is measured compared to distilled water e.g. 1.023.
• 35 ppt is about 1.023.
• I tend to refer to salt level in s.g.

Why does the salt level rise?
This is because salt doesn’t evaporate, so as the freshwater evaporates out the salt level rises.

Why does the salt level drop?
It is sometimes possible for the salt level of an aquarium to drop with out the addition of fresh water this is due to protein skimmer skimming out highly salted water.

How do I raise my salt level?
• You add more sea salt to the running tank (it is best to add a small bit at a time e.g. some per hour, enabling you to monitor the increase to avoid going from low salt to high salt quickly).
• You can do a water change with a higher salt level in the new water.

How do I lower my salt level?
• If your salt level is starting to build up, it is advisable to do a water change, making the salt level in the new water less than it is in the tank.
• If you are using ready-made water to do your change, try to add R.O. water to drop the salt level in the new water. If R.O. water is not available use aged freshwater.
• The new freshwater may need buffing because the hardness will be lower than the tank.
• When you are dropping your salinity check your calcium and alkalinity levels because lower salinity can affect them.
• There are various top up systems on the market that eliminate the need for manual top ups. These can be expensive, but save you time.

What should my salinity be?
About 35 ppt.

What should my specific gravity be?
• I recommend about 1.023 S.G.
• Natural seawater has a salinity of between 1.022 and 1.030.
• Reef tanks can usually withstand being between 1.015 and 1.030.

How do I test for salt level?
• There is a range of hydrometers available on the market.
• Remember the temperature of the water can affect salinity readings. Most hydrometers are designed to be most effective at a temperature of 25’C.
• Refractometers measures salinity in ppt.
• Conductivity is used to measure salt level, the more salt in the water the higher the conductivity will be.

by Paul Talbot