Salinity
- Thread starter svreef
- Start date
sfsuphysics
Supporting Member
Calibrate both with 35ppt standard
ofzakaria
Guest
Make sure you calibrate at room temperature
Coral reefer
Past President
Lower your Tank by .001 and check again tomorrow
sfsuphysics
Supporting Member
Not sure how the Hanna checker works, but you don't want to calibrate with RODI with the refractometer, you want to calibrate closer to the actual value you'll be reading.
Vhuang168
Guest
We ran an experiment at the last talk. Had everyone bring their refracs and calibration solutions. After calibrating, we switched solutions and tested using that. There were more wrongs than rights. Even the 2 Milwaukee’s were off. But off by the same amount.
Sent from my iPhone using Tapatalk Pro
Sent from my iPhone using Tapatalk Pro
ashburn2k
Supporting Member
Even after Milwaukee zero out with rodi water?
Sent from my iPhone using Tapatalk Pro
ofzakaria
Guest
I stopped using Milwaukee after consistently showing at least 1ppt error immediately after RODI calibration.
The funny thing Milwaukee go back and forth on the message of how to calibrate. On the manual it says to use RO, then one day I saw a video of their rep in macna saying you must calibrate rodi not ro
) either will give the error on my unit.Based on my personal experince:
Best digital refractometer was and still is the misco..expensive thu and not worth it for a hobby.
Best refractometer i have is the red sea refractometer if calibrated using RODI, room temperature with good care toward calibrating and cleaning the glass before and after the test.
As for probs wise I have tried all... to me the best was the ghl salinity prob.
Last edited:
Calibrating to 35 ppt will give you more accurate results, but only if your calibration liquid is good.
And they can easily go bad if old and not quite sealed, as they evaporate slightly.
If bad, they can be WAY off.
Thus, if you are not sure, calibrate with RODI.
You will be off by a tiny bit, depending on the quality of refractometer, but never off by an amount that causes problems.
Air temp does not matter that much. Refractometers usually have compensation for that.
And they can easily go bad if old and not quite sealed, as they evaporate slightly.
If bad, they can be WAY off.
Thus, if you are not sure, calibrate with RODI.
You will be off by a tiny bit, depending on the quality of refractometer, but never off by an amount that causes problems.
Air temp does not matter that much. Refractometers usually have compensation for that.
ofzakaria
Guest
Temp matter.... each refractometer is built to yield an accuracy at specific temp range..
If you ask vendors they will all tell you it matter...
My 2 cents, if you want to chase down to 1ppt or leas accuracy you need to follow the rules to the letter. Once we start deviating here and there, inaccuracies start adding up..
Last edited:
ofzakaria
Guest
Some references on impact of temp when using refractometers
www.misco.com
www.redseafish.com
The Secret to Accurate Refractometer Readings
How to get the most accurate readings from a digital handheld refractometer.
Seawater Refractometer - Red Sea Salinity test for marine aquariums
Red Sea’s Seawater Refractometer offers exceptional accuracy, for measuring the absolute salinity of seawater Specifically designed for saltwater aquariums
www.redseafish.com
Last edited:
The_Lazy_Reefer
Supporting Member
My Hanna has been accurate for over a year now with only a calibration every 4 months, wasn’t off but calibrated to check. It measures temp and adjusts the reading accordingly. At this point it has my trust and is hands down the best 65$ I’ve ever spent reefing
Vhuang168
Guest
Used RODI as well as the calibration solution that you can purchase from Milwaukee.
35ppt at room temp is =/= to 35ppt at 78deg F unless the refract is scaled to room temp (whatever that is). If you look at the scale of the refract, there is usually a temp etched there. That scale is only valid at that temp!.
The digital ones like the Milwaukee have a stainless well that I think they use to measure the temp of the sample and scale the reading according to that.
The light used also affects the reading. Units designed to be used out in the field may be designed to use sunlight vs artificial light. Fluorescent light vs LED light vs Sunlight will give the same sample different readings.
The RedSea refractometers are known to not hold calibration - it's much better glass than others but I wouldn't trust it if calibrated more than 5 min ago. Maybe it's some bad batches but I have a bad one and there was a long thread on RC about this issue when RedSea had dedicated forum. My cheap Chinese is more reliable but the scale and optics is worse.
ofzakaria
Guest
I would not take any measurment using smy instrument without calibrating the instrument first.
So indeed, my experimce and openion of the redsea refracto is with calibrating before each measurments.
Vhuang168
Guest
I used RODI to calibrate my Milwaukee and used this chart to make a standard to test it out (from Milwaukee manual). Just used non-Iodized Morton’s table salt and it was spot on.
View attachment 14150
Brine or Salt solution is =/= Sea Water. Lots of other 'salts' make up what is in seawater. Refraction will be different because of that. That is why refractometers scaled for brine are not recommended for aquarium use.
Disagree.
Sure, the refraction index is certainly sensitive to temperature.
But refractometers have a bimetallic strip inside attached to the optics that compensates for temperature.
Plus, unless you store the instrument outside in the sun/snow, it really does not change all that much.
Key though: That bimetallic adjustment is not instant. It needs some time to adjust.
So you need to keep the instrument (not the water) stored in the same place you measure it,
plus you need to give it a few seconds for that little drop of water to adjust to temp of instrument.