Salt Gravity Trouble!!!

coldshot · Jun 18, 2009

That Guy said: ↑

i have done an experiment using 10 hydrometers all of the same brand (instant ocean) where i measured salinity from the same water sample...lined them all up next to each other and got 10 different readings. then did it again with a sample of water of a different salinity. So, the thing with hydrometers is that they vary from one to the other as far as what the readings will be but each individual is always off by the same factor.
For example...lets say i used a refractometer on the water sample and found the sg to be 1.025...
hydrometer #1 would read that water sample to be 1.027
Hydrometer #2 would read it to be 1.023

now lets say you take a new water sample and measure with a refractometer and find a sg of 1.022

hydrometer # 1 would now read 1.024
hydrometer # 2 would now read 1.020

So #1 is off by +2 of the reading with the refractometer
and #2 is off by -2

Now ill get to the point.... If you find a friend or LFS who will check your water with a calibrated refractometer, you can then take the same water sample and measure what your hydrometer reads so you can figure out how much it is off from the refractometer reading. then every time you check with that hydrometer you know how much to add or subtract to get the real sg.
Click to expand...

Is it the same every time or just for the test?
Test with a hydro then wait a few minutes and run th ehydro under warm water then retest the same water.....(just curious)
Danny

That Guy · Jun 18, 2009

i just gave an example using two just so i wouldnt have to type out 1-10....but each individual one was off by a factor of "+/- X" but consistantly off. so to put it simply is that you can use a refractometer to calibrate a hydrometer.
i hope that makes sense

BuckAye · Jun 18, 2009

rayjay said: ↑

Soak the tester in white vinegar overnight and rinse well. Then soak it in salt water for an hour.
When testing, make sure there are no bubbles in the hydrometer.
I personally test three times if the first two readings differ, never testing fewer than two times.
Some new plastic hydrometers need this conditioning before they can be used.
Click to expand...

+1 what I do with mine is flick the hydrometer with my finger until all the little bubbles come off the meter arm. Then the reading is generally accurate. If you are getting a reading in tap water either the meter is broken or the air bubbles are upsetting the reading.

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Salt Gravity Trouble!!!

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