Salinity Disection

James0816

James0816

AC Members
Feb 14, 2007
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Getting ready to take a dive into a major project. I'm still researching and doing tons and tons of reading.

Quick question, when something is referred to as having a salinity level of 1.8-2.0ppt, what exactly does that mean?

So to break it down to where I might be able to understand better, we'll keep it simple. Say I have a 10g aquarium and I want to get my water to that level.

ok...back to the books.
 
"ppt" = "parts per thousand"

a 1 ppt salt solution would have 1 pound of salt dissolved into 1000 pounds of water, or equivalently 1 pound of water would have 1/1,000 th of a pound (0.001 pound) of salt dissolved into it.

10 gallons = 80 pints = 80 pounds

assuming it has 10 gallons of water in it after all the substrate etc. is added -- and technically including the water in the filter system -- you would need to add

1 ppt ==> 80 pound/1,000 = 0.080 pound = (16 ounce/pound * 0.080 pound) = 1.28 ounces of salt

to visualize it, that would be (very roughly) a jigger (1.5 fl. oz) of granulated salt
 
agree w/ Puffer.

While "ppt" is often used in some formal papers (and it seems by Brit hobbyists), it is really only relevant as you are mixing up a new solution. Specific gravity is more accurate, and obviously the only (practical) way to measure an existing water source rather than one you're making from scratch.
 
You should note that a refractometer should be calibrated by pinpoint solution & the hydrometer should be checked against a calibrated refractometer to be sure of correct salinity or you could be way off.
 
pbeemer said:
agree w/ Puffer.

While "ppt" is often used in some formal papers (and it seems by Brit hobbyists), it is really only relevant as you are mixing up a new solution. Specific gravity is more accurate, and obviously the only (practical) way to measure an existing water source rather than one you're making from scratch.
Click to expand...

That's only partially true. While ppt can only get a true calculation with initial mixing, it can be extrapolated with some degree of accuracy (plenty for hobbyists' use). It is independent of temperature, obviously, which makes it more accurate (but not as accurate without the initial solution). "ppt" is not necessarily used by british hobbyists--it is often used in marine biology in general. However, both specific gravity and salinity in ppt have fallen out of favor in terms of both accuracy and usefulness--both have given way to PSU, which is actually based on conductivity.
 
Well, this is a marine project and as of now, I only have ppt to work with until I come up to speed and translate it into SG. But temps will play a factor in that as well so not sure how I can get an accurate read on that.
 
By measurement...do you mean what will I be using to measure such as a hydrometer?
 
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