View Full Version : Salinity #

eric w
05/04/2012, 12:25 PM
Hi all,

My tank has been running for about a week now and has held steady at 1.024....been reading and seems like it should be at 1.026....What should I be at? Thanks

05/04/2012, 12:38 PM
sp gr. should be 1.026 precisely.

Chris Lakies
05/04/2012, 12:42 PM
What are u testing with? If it is a swing arm type hydrometer i would suggest getting a refractometer. Hydrometers can be hit or miss on accuracy.

05/04/2012, 12:43 PM
i have my tank at 1.026-1.027. I find that my corals like it there the best.

Randy Holmes-Farley
05/04/2012, 12:58 PM
I doubt you'll notice much difference between sg = 1.024 and sg = 1.026, but I see no reason to not target the higher level as it is close to the typical ocean salinity. :)

eric w
05/04/2012, 02:07 PM
Im using a refrac...was told 1.024 was a good number..hear so many different things...so would a little higher be better?

Randy Holmes-Farley
05/04/2012, 02:09 PM
There's no rational that makes sense for keeping it lower except lower salt costs.

Here's my rational...

Reef Aquarium Water Parameters

from it:


There are a variety of different ways to measure and report salinity, including conductivity probes, refractometers, and hydrometers. They typically report values for specific gravity (which is unitless) or salinity (in units of ppt or parts per thousand, roughly corresponding to the number of grams of dry salt in 1 kg of the water), although conductivity (in units of mS/cm, milliSiemens per centimeter) is sometimes used.

Somewhat surprisingly, aquarists do not always use units that naturally follow from their measurement technique (specific gravity for hydrometers, refractive index for refractometers, and conductivity for conductivity probes) but rather use the units interchangeably.

For reference, natural ocean water has a salinity of about 35 ppt, corresponding to a specific gravity of about 1.0264 and a conductivity of 53 mS/cm.

As far as I know, there is little real evidence that keeping a coral reef aquarium at anything other than natural levels is preferable. It appears to be common practice to keep marine fish, and in many cases reef aquaria, at somewhat lower than natural salinity levels. This practice stems, at least in part, from the belief that fish are less stressed at reduced salinity. Substantial misunderstandings also arise among aquarists as to how specific gravity really relates to salinity, especially considering temperature effects.

Ron Shimek has discussed salinity on natural reefs in a previous article. His recommendation, and mine as well, is to maintain salinity at a natural level. If the organisms in the aquarium are from brackish environments with lower salinity, or from the Red Sea with higher salinity, selecting something other than 35 ppt may make good sense. Otherwise, I suggest targeting a salinity of 35 ppt (specific gravity = 1.0264; conductivity = 53 mS/cm).

eric w
05/04/2012, 04:02 PM

Randy Holmes-Farley
05/04/2012, 05:09 PM

Happy Reefing. :)

05/04/2012, 10:53 PM

Happy Reefing. :)

Randy,you have a PM.:wave: