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Old 06-20-2004, 11:55 AM   #1
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salinity ??

is there a chart out there anywhere that will show the change in water temperature and salinity?? i ask cause ive always have used a floating type hydrometer and just bought a new larger one and its reading are for water at 75 degrees !! so if my tanks at 80 wouldnt it raise the results?? so a salinity of 1.025 @ 75 degrees would it show for water at 80 at mabe 1.028?? i did a search here didnt find anything close as well as online!! my last one never said what temp it was gauged at but when i had a 2nd test on it i was right on !! any help would be great help :-0
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Old 06-20-2004, 12:03 PM   #2
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it is important to remeber that salinity or PPT does NOT change with temperature but specific gravity DOES change with temp. Higher temp means less dense water so the specific gravity will be lower at higher temps for any given salinity.

for example if you have water at 35 ppt salinity your specific gravity may be 1.025 at 80 degrees but might be 1.028 at 75 degrees. either way your still at 35 ppt salinity.

found this !! does this sound right ??
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Old 06-20-2004, 12:04 PM   #3
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I am an electrician and we deal with specific gravity in batteries and it is 1 point for every 3 degrees
so you add one point for every 3 degrees above what your hydrometer is calibrated at (mine is 75 degrees)
and subtract one point for every 3 degrees below

and this !! would this work as well kinda confused !! i know i need to invest in a refractormeter but so many other things i need/want why i use a floater hehehe
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Old 06-20-2004, 04:27 PM   #4
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for example if you have water at 35 ppt salinity your specific gravity may be 1.025 at 80 degrees but might be 1.028 at 75 degrees. either way your still at 35 ppt salinity.

found this !! does this sound right ??
That's almost correct. A higher temp will generate a higher SG, not a lower temp. Salinity is unaffected by temp.

Specific Gravity

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Old 06-20-2004, 04:35 PM   #5
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Quote:
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Quote:
Originally Posted by scuba_steve
for example if you have water at 35 ppt salinity your specific gravity may be 1.025 at 80 degrees but might be 1.028 at 75 degrees. either way your still at 35 ppt salinity.

found this !! does this sound right ??
That's almost correct. A higher temp will generate a higher SG, not a lower temp. Salinity is unaffected by temp.

Specific Gravity

Cheers
Steve
So, to get the correct sg when mixing water, you just want to make sure you have the water at the temp that you want it at when you take your readings?
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Old 06-20-2004, 11:32 PM   #6
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Kind of but it's the reading of the hydrometer that's being affected, not the salt content.

The accuracey of the reading depends on the quality of the instrument used and how well calibrated it is. If using a refractometer and measuring the salinity at 35 ppt (1.025 SG) it makes no difference what the temp is. If using a swing arm hydrometer the same is not true. If you target an SG of 1.024-25 @ 80¬į, you should be safe though.

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Old 06-21-2004, 10:05 AM   #7
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I've wondered the same thing because the tests I've conducted with a swing arm did not show a difference in SG for water temps of 75 and 80degs.
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Old 06-21-2004, 10:48 AM   #8
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The difference will become apparent once the swing arm gets a bit older.
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Old 06-21-2004, 11:03 AM   #9
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yea i never liked using swing arm style hydrometers but like the glass floating type !! but never had one that stated it was set at 75 degrees this some german quite large one
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