A few salinity questions

vivioo7

vivioo7

Member
I just got a refractometer today and have been doing some reading so now I have 2 questions. The first is: if specific gravity varies based on temperature but ppt doesn't do fish need a constant SG or ppt? That might be kind of confusing, for example do fish (and other reef animals) need a constant SG regardless of what the ppt is or vice versa? I hope everyone can understand that. My other question is since temperature affects SG and not ppt but my refractometer has a straight line so that there can be no variance for temperature, how does it give an accurate ppt reading?
I know they aren't worded the best hopefully everyone can understand what I'm asking
 
bruner54

bruner54

Member
yes fish and reef animals need a constant sg and i think wen your talking about temp affecting the sg its wen your mixing the salt it helps to have warmer water cause the salt dissolves better but temp changing in the tank does not change the salinity. hope this helps
 
namas05

namas05

Member
The short answer is Yes,,lol
PPT (parts per thousand) will not change with temerature. If you have 1000 grains of salt take one out and add one grain of pepper you will always have 1 ppt pepper no matter what the temperature is.
SG (specific gravity) can change with temerature yes that is true, but the amount of change in our tank enviroment is so minimal that it cannot be identified by simple testing or by our tank inhabitants.
SG is a relative measurement to water. a specific gravity of 1 is equal to one gallon of water. Water has a density of 8.33 ppg (pounds per gallon) at room temperature (77F), of course that is a relative number. As water is heated it expands therefore the density will drop. But to have a drastic difference you will need to heat the water more than just 4 - 5 degrees.
So unless your tank temp is way over or way under 77F there will be no detectable differences.
Hope this makes sense to some one besides me. Or if you need more info let me know. And I will try to answer your questions.
 
namas05

namas05

Member
SG is a measurement of weight. How much the salt water weighs.
Salinity has to do with the amount of salt in the water. PPT So it is a measurement that has no bearing on the tempurature or gravity. It is a count of the particles of salt within the water.
 
vivioo7

vivioo7

Member
The reason I asked is because when I calibrated my refractometer I was wondering if I didn't do it at the right temperature and how much that would affect the readings. I had some distilled water at room temp (about 77) and used that as 1.000, my tank is at about 77 degrees too so does this mean the readings will be accurate?
 
namas05

namas05

Member
Yes.
If at 77F the SG is 1.025 even at 85F it would probably only change to 1.0249987(this is not a factual number) just as an example.
 
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