Red Sea refractormeter

[Camaro Show Corals]

So I bought a Red Sea one so I stop using a hydrometer and I’m having so issues with it so i don’t have any calibration fluid I hear that’s the best way to calibrate it but you can also use ro water but just for kicks I put some of my saltwater on it and I got the reading of 1.010. I need some help getting it set up. I can’t go buy calibration fluid because the closest lfs is a hour away

 

[DSC reef]

I have the same refractometer. I strongly recommend getting some calibration fluid. We order ours from satwateraquarium.com and it's pretty cheap. I'd use the hydrometer until you get fluid and make sure you calibrate before every salinity check.

 

[AdamNC]

I’ve used both RO/DI and calibration fluid on my Red Sea Refractometer and haven’t noticed any difference. For the past 4 years I’ve used RO/DI. If RO/DI didn’t work I don’t think my tank would still be alive.

 

[Randy Holmes-Farley Verified Community Expert]

The Red Sea refractometer claims to be a true seawater refractometer (most are not) so if it is properly made, calibration with ro/ di will be fine. Checking the calibration with a standard can double check that.

 

[DSC reef]

I’ve used both RO/DI and calibration fluid on my Red Sea Refractometer and haven’t noticed any difference. For the past 4 years I’ve used RO/DI. If RO/DI didn’t work I don’t think my tank would still be alive.

It will work but there was a difference for mine. Not enough to kill a tank but a difference still. There might be differences in the quality of RODI being used so I wonder if that can throw the calibration off?

 

[AdamNC]

There might be differences in the quality of RODI being used so I wonder if that can throw the calibration off?

That could be a possibility.

 

[chipmunkofdoom2]

So I bought a Red Sea one so I stop using a hydrometer and I’m having so issues with it so i don’t have any calibration fluid I hear that’s the best way to calibrate it but you can also use ro water but just for kicks I put some of my saltwater on it and I got the reading of 1.010. I need some help getting it set up. I can’t go buy calibration fluid because the closest lfs is a hour away

If you don't have a refractive index standard available, calibrating with fresh water is likely better than nothing. Try calibrating to with freshwater and seeing what your tank's salinity is. If it's close to what the hydrometer said (+/- a few ppt), then the reading is likely good enough for now. I would encourage you to get a salinity standard when you can to verify the results.

 

[chipmunkofdoom2]

I’ve used both RO/DI and calibration fluid on my Red Sea Refractometer and haven’t noticed any difference. For the past 4 years I’ve used RO/DI. If RO/DI didn’t work I don’t think my tank would still be alive.

For some people, calibrating with freshwater will produce the same results as a refractive index standard (it sounds like you're one of these people). However, that's not a guarantee for several reasons. One of them is not all refractometers are designed to measure seawater (as Randy alluded to above) and won't be able to accurately measure seawater when calibrated with freshwater. Another is that not all refractometers have perfect internal calibration. Calibrating with freshwater simply means that the refractometer will read freshwater accurately. As the salinity of the sample being measured goes up, so does the potential error (see Figure 17 in Randy's article on the topic).

For you and other reefers, calibrating with freshwater seems to work. For others, it does not. None of my refractometers ever read a salinity standard correctly when I calibrated with freshwater. Calibrating with a refractive index standard means that you will always measure accurately at S = 35ppt, no matter what. Calibrating with freshwater only provides 100% accurate results in some cases. For me, this is a good enough reason to always use a calibration standard. They're not expensive ($10 on BRS), and Randy even wrote an article about how you can make your own.

Calibrating with freshwater will likely produce the same results, even if they're wrong, so it's probably good enough. Reef aquaria can survive at a wide range of salinity. Does it matter if you think your tank is at S=35 ppt when in reality it's S=33.5 ppt? Probably not. Having said that, I personally don't think that "good enough" is acceptable when you can know for sure for only a few bucks. But, to each his own.