measuring salinity

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vombatus

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Dec 1, 2008
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I am still having trouble with my hydrometers (I have two different kinds). I know some of you advocate refractometers instead, but it's not quite in my budget right now. What I don't understand is, how come when I do a water change and add salty (Instant Ocean) water to my tank and then measure it with the hydrometers, the things seem to say it's freshwater? But if I come back the next day and measure again, I'll get a reading of a higher SG! Does the salt need time to disperse or something? My tank has great water circulation and only less than 10 gallons of water in it. Despite these problems with measuring every time I change the water, my mudskippers and mollies are doing great. So I must be doing something right. I just worry about the lack of precision with which I add the salt-- honestly, I eyeball it. :(
 
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Amphiprion

Amphiprion

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Feb 14, 2007
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vombatus said:
I am still having trouble with my hydrometers (I have two different kinds). I know some of you advocate spectrometers instead, but it's not quite in my budget right now. What I don't understand is, how come when I do a water change and add salty (Instant Ocean) water to my tank and then measure it with the hydrometers, the things seem to say it's freshwater? But if I come back the next day and measure again, I'll get a reading of a higher SG! Does the salt need time to disperse or something? My tank has great water circulation and only less than 10 gallons of water in it. Despite these problems with measuring every time I change the water, my mudskippers and mollies are doing great. So I must be doing something right. I just worry about the lack of precision with which I add the salt-- honestly, I eyeball it. :(
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Yes, the salt needs time to diffuse throughout the solution. Mix the water in the container and preferably use a powerhead to keep the container water circulating. Measure it several minutes later to check the salinity. Allow that to circulate until the next day before you use it. It may also be a good idea to test again before use. Also be aware that if the water isn't fully mixed, you'll get freshwater on the top and saltwater on the bottom, since the latter is denser than the former.

FWIW, decent refractometers only cost ~$40. You may require a seawater standard (if your brackish range is close to seawater) or distilled water (if it is closer to full freshwater).
 
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rustyfan21

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Oct 9, 2008
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I recently purchased a refractometer on ebay for $35 and free shiping. Just an idea where to look. Best investment I made.
 
Blown 346

Blown 346

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Dec 7, 2008
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Standing kind?? Is that the clear plastic one with the little pointer?? If so I threw mine out along time ago, it gave me false readings as the needle stuck and wasnt very accurate when it was new.
 
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