Hydrometer calibration

[ed71]

From reading online pages, I take it the process for calibration of the hydrometer is to use distilled water to see the actual exact reading. Well mine reads two marks below 1.000 at 20C. What causes this problem? I just bought my hydrometer a few months ago. Is this a common problem?

Ed

[TheDarkSide]

I haven't used on in years but it's been known to happen. Sometimes the paper slips.

Just give it a little spin and check again (making sure no bubbles are stuck to it ).

If it reads that way again, just adjust based on that calibration, i.e. add 2 points to your reading.

[spiderwrangler]

I don't even think that distilled is necessary, but yes, if yours is a touch off, just keep that in mind. Bubbles won't make it read low, but might make it read high (as they slightly lift the hydrometer).



While typing that I had a thought... soap molecules are bigger than water molecules, but since they affect surface tension, might it lower a reading? Ran to the kitchen, and as predicted, adding soap increases the SG. So does a residual amount of Star San. So common liquids that may be residual in your test jar aren't causing a low reading either.

[TheDarkSide]

Bubbles won't make it read low, but might make it read high (as they slightly lift the hydrometer).

I always tell people to spin it to make sure he isn't off more than he thinks.

[brewinhard]

Distilled water close to your temp that your hydrometer is most accurate at is the best way to go for proper calibration.

[Brewsnail]

Neither my hydrometer nor my refractometer show any difference between my tap water and deionized water (which I got from work)

[Ozwald]

Neither my hydrometer nor my refractometer show any difference between my tap water and deionized water (which I got from work)

Depends on your tap water. Some places have extremely low mineral content, some places don't.

[Brewsnail]

Neither my hydrometer nor my refractometer show any difference between my tap water and deionized water (which I got from work)

Depends on your tap water. Some places have extremely low mineral content, some places don't.

Yes, the tap water here has really low mineral content. According to the water report the sum of all positive metal ions is about 40 ppm, sulphate and chloride 50 ppm together.

But with an addition of table salt (NaCl) to my tap water.
SG : ppm NaCl
1.000: 1000 (didn't taste this one)
1.001: 2000 (Doesn't taste too bad, but it has an off flavor from the salt, I would prefer not to drink this)
1.002: 5000 (I would not call this drinkable, far too much salt flavor)

(1000 ppm = 1 g salt / liter of water)

So I can taste the difference before my hydrometer shows all that much, but that's with table salt, a cheap hydrometer and a pretty good scale. I'd say that my hydrometer is not good enough to notice small amounts of dissolved minerals, you'd probable need something really fancy for that.