Salinity Please help me make sense of this

[KStatefan]

Mix up some of Randy's hydrometer standard and verify your hydrometer is correct. My Hanna always reads 0.001 lower then my hydrometer. When I test salinity I let the hydrometer, water and glass cylinder equalize temp then use a formula to get actual S.G.

The number I get on my controller I just use as a reference.

 

[Malum Argenteum]

Shouldn’t the hydrometer be the most accurate since it doesn’t require calibrating?

It isn't that it doesn't require calibrating, but rather that it cannot be calibrated (though that isn't true, really; you can measure a known standard with it and make a mental or other note as to how far off the thing reads, and then do the math each time you use it).

Something that cannot be calibrated, if it is reading incorrectly, will continue to read incorrectly, but that doesn't make it accurate.

 

[gbroadbridge]

Same sample different Hanna’s. All Claire’s day of.

The difference between those 3 measurements is completely insignificant for a reef tank.

These are hobby grade testers, not $5000 laboratory instruments.

Pick any of one them and stick to using just that one.

 

[Pod_01]

So,
- Hanna shows 32.5 PSU
- TM Hydrometer 1.0252 (based on picture) is 33.5 PSU
- Apex shows 31.3 PSU

From where I stand that is pretty good consistency for hobby test kits. As mentioned above pick one and stick with it.

For example I use my GHL to track general trend, salinity is going up or down and I use the TM Hydrometer to decide what it is.

Also I find for accuracy the GHL probe requires frequent cleaning, biofilm that grows on it will impact the readings.

Good luck,

 

[ReefHunter006]

If I choose to go with the Hanna’s and the hydrometer is right then I would be overshooting my target salinity by 3ppt to 38ppt in this case. That seems a bit excessive and not a small error.

 

[Pod_01]

If I choose to go with the Hanna’s and the hydrometer is right then I would be overshooting my target salinity by 3ppt to 38ppt in this case.

I am not following, but perhaps I miss something. Is this not correct?
- Hanna shows 32.5 PSU
- TM Hydrometer 1.0252 (based on picture) is 33.5 PSU

In the initial post.
That is 1 PSU!!!

Just to make sure we are not mixing apples and oranges.
TM Hydrometer is measuring relative density not density (g/cm^3). Relative density has no units, density on the other hand has units.
Here is label on my TM Hydrometer.

I believe only TM Hydrometer sold in Germany measures Density….

Below is conversion between the various measurements:

So from your pictures I see TM Hydrometer measuring 1.0252 rel. density at 23.2 degrees.

My interpretation…