Hydrometer temperature correction

[Cory]

What is the SG of my tropic marin floating hydrometer if it reads randys diy calibration standard at 1.0284 and the sample temperature was 18 C?

 

[Shirak]

Does it say on the hydrometer what temperature it was calibrated at?

 

[Shirak]

If I am reading the online info correct it's calibrated to 77 or 25 C.

If that's correct. Then 1.027

 

[Shirak]

Nice little handy calculator for SG temperature correction.
https://www.morebeer.com/content/hydrometer_correction_calculator

 

[Cory]

Yes thats correct 77f or 25c is the calibration temperature of the hydrometer.

 

[Shirak]

Yes thats correct 77f or 25c is the calibration temperature of the hydrometer.

What is the standard SG at 18 C?

 

[Cory]

What is the standard SG at 18 C?

Not sure i understand the question. But Randy's solution is supposed to be at 20 c iirc.

 

[Shirak]

Which standard did you make? The 1.02660 at 20C?
If so, at 18C the SG is higher than 1.02660

 

[Shirak]

Can you warm up the standard to your tank temperature and then measure?

 

[Cory]

Which standard did you make? The 1.02660 at 20C?
If so, at 18C the SG is higher than 1.02660

I made randys diy hydrometer standard so:

To produce a 3.714 weight percent sodium chloride solution, dissolve 1 teaspoon (6.20 grams) of Morton's Iodized Salt in 161 mL (161 g) of freshwater (making a total volume of about 163 mL after dissolution of the salt). This solution can be scaled up as desired.

I did this scaled up 5x. So 31 grams of salt in 805 g of ro water.

 

[Cory]

Can you warm up the standard to your tank temperature and then measure?

Yes i was thinking i should do that too lol

 

[Shirak]

I was reading Randy's article on hydrometer and standards.
I think if you can warm it to 77-78 and then measure you should be reading 1.0264 SG using his 3.714 percent formula. That would give you the correction factor for your specific hydrometer.

"For standard floating hydrometers (Figure 2), which are not self-correcting for temperature variations, it is important to use the standard at the same temperature at which the aquarium water will be tested (within say, ± 0.5 ºC or ± 1 ºF). Preferably, that will also be the temperature at which the hydrometer is intended to be used (often marked on it), but that is not an absolute requirement. The aquarist can then mark on the hydrometer the level to which it rises (that is, the water line), and use that as an indication of the specific gravity of S=35 seawater, which has all of the properties listed in Table 1(specific gravity = 1.0264, etc). If the hydrometer reads higher or lower than 1.0264, then the aquarist can just imagine the scale on the hydrometer to be shifted up or down, and shift all other readings taken with it (at the same temperature) by the same amount."

 

[Reef.]

1.0268 SG

 

[Shirak]

I am guessing your hydrometer is pretty close as the online calculators still say a hydrometer calibrated to 77 F and reading a solution at 18 C at 1.0284 would give a reading of 1.027 which is pretty darn close to 1.0264 So if anything it's reading around 0.0006 high

edit. ok so it's about 0.0004 high then?

 

[Cory]

Thanks guys

 

[Cory]

Im curious what Randy thinks?

 

[Randy Holmes-Farley]

Im curious what Randy thinks?

The calculators should be fairly close for correction. Seawater may be a little different than fresh water.

 

[Cory]

The calculators should be fairly close for correction. Seawater may be a little different than fresh water.

I used your chart for the tropic marin hydrometer in your article but it doesnt go below 23c so i had to figure it out. Is there a way to figure it out from the chart?

 

[Randy Holmes-Farley]

It's better to use a calculator than extrapolate from a table.

 

[Reef.]

I used your chart for the tropic marin hydrometer in your article but it doesnt go below 23c so i had to figure it out. Is there a way to figure it out from the chart?

I use this one, I can’t say how accurate it is, seems to be.

Salinity Correction Calculator

Aquarium calculator; Correct a relative specific gravity (sg) measurement taken with a non-temperature-correcting unit.

www.hamzasreef.com