I recently purchased an acquamarine refractometer for use with my 600g reef tank. The specific gravity vs 0/00 on the scale does not correspond to those which I read in books. Is this a result of this particular meter being calibrated at 20 degrees C vs 25 degrees which is what all the books refer to. If so, which scale should I use to set my tank salinity. A sp gravity of 1.022 or a 0/00 of 33 (these do not correspond with each other on the scale on this device)I suspect that I should use the concentration (0/00) scale since it should not vary with the temperature.
Acquamarine refractometer
- Thread starter texman
- Start date
I use the ppt scale. The meter should adjust to temperature after 30-60 seconds. I calibrated mine at room temp (75F) and it works well. I would suggest that you consider a higher salinity than 1.022. Most reefs in the world are at about 35 ppt salinity, or a specific gravity of 1.0265.
Ernie
Ernie
esm,
With the refrac, you put the sample on the glass and close the plasitic 'top', then wait for 30-60 seconds, then read the 0/00 side or specific gravity side?
Are you also saying that at 0 seconds the reading might come up as one number, but waiting the 30-60 seconds may give a different, but temperature calibrated reading?
I know it's supposed to be simple!
With the refrac, you put the sample on the glass and close the plasitic 'top', then wait for 30-60 seconds, then read the 0/00 side or specific gravity side?
Are you also saying that at 0 seconds the reading might come up as one number, but waiting the 30-60 seconds may give a different, but temperature calibrated reading?
I know it's supposed to be simple!
I read mine on the Specific Gravity side, but I double check the ppt side also. The reading may change as the device adjusts to the temperature of the water. I have never noticed the reading to change, though, but that was what the book said. It said to wait 30 to 60 seconds before taking the reading.
Ernie
Ernie
I realize that it is important to wait for the temperature to equalize. What I am talking about is that the ppt scale does not match the specific gravity scale as described in most books. For example, in Knop's clam book (pg 151, a ppt of 33 corresponds to a specific gravity of 1.022, whereas on this device, a ppt of 33 corresponds with a specific gravity of 1.026. I believe this difference is because this meter assumes a temperature of 20 degrees C, while the book assumes that we are comparing the two at 25 degrees C. When using this meter, therefor, I think that one should set the tank to about 35 ppt vs trying to set it to 1.022 which according to the meter would set the ppt around 28. ?yes, ?no
Unless the temp of your water is at the extreme ends, the refractometer's ambien temp (assuming you keeping it at room temp of about 75F)should be more than enough to equalize the temp from a couple drops of water. I don't think waiting for 30 sec would make a difference. JMO.
hi.
But the problem is that refractometer does not measure concentration directly. There is no direct relationship among concentration/density/conductivity/refractive index unless you know exactly the ratio of every type of ions (and dissolved chemicals) in the water. This is a common misconception among reefers that there is a 1:1 relationship among the measurement mentioned above. A thermometer with both F and C scale, and we can read 0C-> 32F. But the similar side-by-side scale in swing arm hydrometer and refractometer has two different units that is not directly convertable. The reason that most of the indirect measurement of salinity works so well in this hobby is because two of the most abundant ions, Na and Cl, overwhelm all the other ions in the sea water.
The original poster's question was never answer. My hypothesis is that different assumption of the ions in the water lead to the differences between the refractometer's "conversion" between density and concentration, and reef book's "conversion" between density and concentration.
Most refractometer uses a bimetal strip attached to the optics inside to compensate the temperature.
Sponsor Reefs
We're a FREE website, and we exist because of hobbyists like YOU who help us run this community.
Click here to sponsor $10:
