got ta ask :p

[Kwater]

ok this has been driving me nuts.
it is a queston relating to salinity and specific gravity. now, i know that specific gravity is the comparsion of a liquid ( in this case saltwater :p ) to that of pure fresh water witch has a density of 1.000 g/cm3. and salinity is the amount of ions in solution in a leiter of water. so salinity is what it is and specific gravity is the measurment that most of us hobbiest use im assuming because i dont know of anyone that has a salometer, that would be chill though. so if u are standing in front of youre aquarium it would be correct to say that youre specific gravity is 1.025 ( assuming it is of course ) right???? because you would not be able to say that youre salinity is 1.025 because that is not what the salinity is, that is the specific gravity, A WAY OF MEASURING SALINITY not the term given to salinity correct????? i just really want to clear this up just for myself. thanx a lot

 

[little_fish]

Salinity is just how salty the water is, and while its typically expressed as a percentage, i do believe you can still express it as we typically do, because its still a measure of how salty the water is.

Specific gravity of anything is found dividing the density of the solution in question by a reference solution, usually water, making it unitless, which seems to be the favorite state of chemical engineers.

 

[tankedchemist]

just look at the units. Salinity is either 3.5% salt, or 35 ppt, which is the same as saying 35 grams of salt per liter of solution. It's a measure of weight/volume.

Fish already pointed out the units of specific gravity. For what it's worth, I use specific gravity because hand held refractometers already adjust for temperature dependance. BTW, density of water is only 1 g/cm3 at around 4C, so that's not correct for the water at our tank temps. :) however, the scale on a good refractometer just factors that difference in.

 

[Kwater]

just one other thing i dont understand and have never been able to figure it out is why temp is important to salinity and specific gravity???

 

[little_fish]

Because temperature effects the bonds between molecules, and therefore the overall properties of the substance at that temperature. So at higher temperatures things tend to be less dense because there is more space between the molecules because they have more energy.