1.3.6 Testable Parameters: Specific Gravity
Description
This article is from the ReefKeepers FAQ, by several authors (see the Credits section).
1.3.6 Testable Parameters: Specific Gravity
* Short form:
* Specific Gravity is temperature dependant. See the next table for
* a quick lookup of the recommended hydrometer readings. They are
* based upon our recommended S.G. of 1.025 at 60 degrees F.
*
*Degrees F. Hydrometer reading.
* 50 1.0255
* 55 1.0252
* 60 1.0250
* 65 1.0246
* 70 1.0240
* 75 1.0233
* 80 1.0226
* 85 1.0218 (rather hot for most tanks)
* 90 1.0210 (very hot for most tanks)
*
* In more detail:
* 1.025 recommended for reef tanks. Note that virtually all hydrometers
* are calibrated for measurements at a temperature of 60 F. Included
* below is a short table of temperature adjustments. Add the value
* shown to your hydrometer reading to get an accurate reading.
*
*Degrees F. Correction
* 50 -0.0005
* 55 -0.0002
* 60 0.0000
* 65 0.0004
* 70 0.0010
* 75 0.0017
* 80 0.0024
* 85 0.0032
* 90 0.0040
*
*For example: If the hydrometer reads 1.0235 at 80F, the actual
* Specific Gravity is 1.0235 + 0.0024 = 1.0259
*
*Note: If your tank is between 75F and 80F, this means you should
* try and keep your Specific Gravity around 1.0230 to 1.0235.
*
*For all practicle purposes, the scale is linear between data points,
*so you can simply extrapolate between table entrys. For instance,
*78F is 3/5 the distance between 75F and 80F; the difference in corrections
*is 0.0024-0.0017 = 0.0007. 3/5th of 0.0007 is 0.0004. Add the offset
*0.0004 to the base value for 75F of 0.0017 and you get a correction
*value for 78F of 0.0021.
*
*It is fairly common in literature to see references to salinity in terms
*of Parts Per Thousand (PPT). For salinities in the range we are interested
*in, the conversion formulas are:
*
* Salinity = 1.1 + 1300 * (Temperature corrected Specific Gravity - 0.999)
* Temperatur corrected Specific Gravity = ((Salinity - 1.1) / 1300) + 0.999;
*
*Here is a short table of some common values:
*
* Salinity Specific Gravity
* 20 PPT 1.0135
* 25 PPT 1.0174
* 30 PPT 1.0212
* 35 PPT 1.0251 * Typical Ocean Value *
* 40 PPT 1.0289
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