Refractometer, make sure it's calibrated.
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Randy Holmes-Farley
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What they neglect to tell you is calibrating with a 35 ppt standard will eliminate that concern.
Brian Kim
Color My Reef
I am also having problems with my refractometer and was only able to test it using RO water from 3 different sources. Here's the deal...tested using RO water from 2 different lfs and they both matched. However, I was getting o.05 difference each time I tested using my RO water (even tap water)
Then I thought temperature could affect the results so I ran a test by heating my RO water to 100 degress...my refractometer was now off by 0.10
It is my belief that using 53.0 mS is the best solution. However, I think that you will get different readings if you do not test the water at 78 degrees as recommended by the salt mix makers
Then I thought temperature could affect the results so I ran a test by heating my RO water to 100 degress...my refractometer was now off by 0.10
It is my belief that using 53.0 mS is the best solution. However, I think that you will get different readings if you do not test the water at 78 degrees as recommended by the salt mix makers
Randy Holmes-Farley
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Temperature has a huge impact on refractive index measurements. Many refractometers have a feature that compensates for temperature changes (called ATC), but none are designed to compensate for changes that large. Typically they may claim ranges such as 60-80 deg F or 5-30 deg C, 10-30 deg C etc.
Brian Kim
Color My Reef
Thanks, that was my issue
Brian Kim
Color My Reef
So yeah, guess we can add that to the list, to get the water temperature close to your water temperature before calibrating your refractometer 
especially with cold winter weather ahead of us
especially with cold winter weather ahead of us
marinelife
SaltGeek
also to add to this, replace you calibration fluid as well. I calibrated my refractomter and used older calibration fluid. It was off alot, took my salinity to about 1.032. My tank has never been the same, still working on fixing the mess it cause. I ended up testing my refractometer against 2 others just to make sure I was correct.
gmastr85
Active Member
I've been using the same meter for a couple years. Never had a problem. Mix my salt the same everytime. Check my salinity about once a month. Usually it deviates between 1.025 and 1.026 somewhere. Guess its a good time to calibrate. I'm confused though by what everyone is saying? Is it okay to use DI water or should I use calibration solution. And should I calibrate at room temp, tank temp, or something else? Everyone has a different opinion but what would work best? My refractometer is from BRS. Thanks!
Jlobes
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how old was your fluid? did you often leave it uncapped/open to the air? cant think of a reason for that, other than evap
mandarin417
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My Red Sea Refratometer had to be calibrated each week because of drift for some reason. I purchased a Milwaukee MA887 Seawater Digital Refractometer and I always test first distilled water before testing my saltwater. It reads 1.000 SG every time. I decided to check my reference solution and it matched perfectly at 1.025. This device is a dream to me and I don't have to squint into the refractometer anymore.
mandarin417
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My Red Sea Refratometer had to be calibrated each week because of drift for some reason. I purchased a Milwaukee MA887 Seawater Digital Refractometer and I always test first distilled water before testing my saltwater. It reads 1.000 SG every time. I decided to check my reference solution and it matched perfectly at 1.025. This device is a dream to me and I don't have to squint into the refractometer anymore.
Randy Holmes-Farley
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Randy Holmes-Farley
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This isn't an opinion issue. It is science with one correct answer, and some other answers that may sometimes work and sometimes not.
Calibrate with a 35 ppt standard, and do it under the same room temperature conditions that you measure the tank water. The temp of the actual water is not so important as it quickly approaches the refractometer temp when put on it, especially if it is an ATC refractometer (it will say and most are). Having temp within the prescribed range of the ATC is desirable.
There are some refractometers that RO/DI works out OK as well, but not all. If you don't know for sure which yours is, use the 35 ppt standard.
marinelife
SaltGeek
It was a few years old and never left open. For some reason it went bad, I would have never thought of it but had many issues with my tank, so I check with a friend and I was way off on salinity.
Randy Holmes-Farley
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Evaporation is the only possibility, aside from being contaminated by adding something back into it. But liquids in plastic containers do evaporate over long periods of time. I have old plastic milk jugs of emergency water in the basement. Some have been there for many years and are only half full now.
Randy Holmes-Farley
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Depends on how far off it is when you recalibrate. If it is off by more than your acceptable margin of error, it may be too infrequent.
If it stays basically calibrated each time, then maybe it is more often than needed.
Regardless, any time you get an unexpected reading that might cause you worry or cause you to do something with the tank, first recheck the calibration.
jd371
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I used RODI water to calibrate my Refractometer, but after reading this thread I purchased calibration fluid and calibrated the Refractometer again to find that it was .004 lower than it should be. My tank was at 1.021 all this time! I swapped the ATO water with 1.026 water last night and checked the salinity this morning and it's still the same, how long should it take to raise the salinity?
redfishbluefish
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Can't say without knowing details...total tank volume, amount of evaporation per day.
As an example, if I calculated correctly, if we assume you lose 1 % of total volume every day to evaporation, it will take approximately 19 % of total volume to raise salinity from 1.021 to 1.026 using 1.026 as top-off water.
And slow is the way to go!
As an example, if I calculated correctly, if we assume you lose 1 % of total volume every day to evaporation, it will take approximately 19 % of total volume to raise salinity from 1.021 to 1.026 using 1.026 as top-off water.
And slow is the way to go!
mandarin417
Active Member
Hi Randy. The standard I use is from Naslow Chemical Ltd. called Seawater Calibration Solution. 1.025 SG. To be honest I have no idea where I purchased this product and a google search doesn't seem to find it anywhere.
