HELP Using the Hydrometer

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Aquarium Advice Apprentice
Dec 19, 2004
I'm in the process of mixing my salt and have an Instant Ocean Hydrometer. I would assume that when the water w/o is in the hydrometer that the reading would be at 0 salinity, but for some reason it's reading at 40PPT, what am I doing wrong??
Have you used this hydrometer in salt water before. If not rinsed with freshwater after use some salt can buildup on the arm and be mixing with your new sample. You might also check for air bubbles on the arm making it rise. Give it a couple of taps to see if it goes down. Hope it is one of these easy fixes
Your regular water source is readin 40PPT without any salt? If so this could be a buildup in the hydrometer itsself. Fill it with vinegar and let it sit overnight see if this helps if not your hydrometer is not calibrated correctly which is very common. IMO if you are serious about this hobby a swing arm is not the best way to be going you should try a refractometer which are fairly cheap and are there weight in gold when measuring salinity HTH
If it is new it is probably bubbles on the float. I had that problem too and bought a refractometer and it is great.
Do you always dip a hydrometer near the surface or about midway under the water? I'm curious on how to get the most accurate reading.
You do not want a surface sample. Approx. 6 inches down is what I do. That is probably instilled in me from my 1st hydrometer(deep six) which states that is the best depth. That deep six also talked about seasoning the tester by adding salt water and letting it sit full for 24hrs. Not sure what the affect is if you dont season the hydrometer or if your brand recommends this procedure.
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