ATC Refractometer Question

[CallMeLloyd]

I have a ATC refractometer and when I first got it, it says to calibrate it using RODI water and set it to the bottom line which is 1.000 (0). I have been using it for a few months and randomly remembered that you may have to recalibrate it sometimes. So I checked it with RODI again and it was at 1.010 (10). So I put it back to the bottom line. I went ahead and bought some BRS Refracto Juice. When using the fluid it says it’s at 1.030. So should I calibrate it with the fluid or what? So confused, I have no idea what the salinity actually is in my tank…

 

[dedragon]

Refractometers should be calibrated with calibration solution (refracto juice is one of them) to the level on the bottle. You shouldnt ever use rodi to calibrate refractometers
That being said the refracto juice should be calibrated to 1.0264

 

[dedragon]

The reason ATC might recommend calibrating to 1 is if you needed to use a very low range salinity for another application and not for saltwater fish tanks

 

[CallMeLloyd]

on the ATC refractometer it measures at 20C. According to the bottle I should get a reading of 1.3394?

 

[dedragon]

No that is the refractive index not the specific gravity which is used in the refractometer, the numbers inside are already converted to sg and ppt

 

[CallMeLloyd]

So use to juice, set it to 1.026 and then check tank water?

 

[dedragon]

I guess it would also matter your specific refractometer but they usually have those readings and are not read out by their RI (refractive index). A good way to check would be to see if the 35ppt matches up to 1.0264 sg

 

[CallMeLloyd]

This is what it shows with the liquid.

 

[dedragon]

yep, sg and ppt so you can calibrate to 1.026 or 35ppt as they are the same and you are good to go

 

[CallMeLloyd]

Okay so it’s just a little too high and dial it in to the 35ppm. And then check tank. Does the temp of the water I test matter? My tank is running at 79F. I guess I should just let it sit on the slide for a minute to temp match the refractometer?

 

[dedragon]

I dont really know anyone doing that because I dont think temperature will effect the reading too much. Stable levels are more important, but you can let the temperature drop before hand for a more accurate reading

 

[CallMeLloyd]

Okay just tested tank water it was at about 1.021. I’ll slowly bring it up to correct level. Thank you for your help!

 

[nereefpat]

Okay so it’s just a little too high and dial it in to the 35ppm. And then check tank.

Exactly.

Does the temp of the water I test matter? My tank is running at 79F. I guess I should just let it sit on the slide for a minute to temp match the refractometer?

That is my understanding.

 

[CallMeLloyd]

If I don't top water off with rodi water for a few days and you can clearly see the water level has lowered, wouldn't you think I should have higher salinity readings? I've checked my salinity for the past 3-4 days and I am getting the same readings without top offs.

As far as calibration goes when I use a fluid it reads 35ppm and when I use rodi water its a little below the 0 line.

 

[Randy Holmes-Farley Verified Community Expert]

As far as calibration goes when I use a fluid it reads 35ppm and when I use rodi water it’s a little below the 0 line.

That’s fine.
You may also just not have the resolution and accuracy to see the salinity rise in only a few days.

 

[CallMeLloyd]

That’s fine.
You may also just not have the resolution and accuracy to see the salinity rise in only a few days.

Bought a hydrometer and tested water it says 1.040. I don't know which is right.... how many days does it take for you to see that the salinity has gone up using a refractometer?

 

[nereefpat]

Bought a hydrometer and tested water it says 1.040. I don't know which is right.... how many days does it take for you to see that the salinity has gone up using a refractometer?

What specific hydrometer?

 

[Randy Holmes-Farley Verified Community Expert]

Not sure what scenario you are referring to, but salinity does not take more than a couple of minutes to equilibrate and be properly detected in a single aquarium (no extended sumps and such). .

 

[CallMeLloyd]

It's the Coralife "Six Deep Hydrometer". I went by the hydrometer and brought salinity down to 35ppm. Refractometer still reads the same as before.

 

[nereefpat]

It's the Coralife "Six Deep Hydrometer". I went by the hydrometer and brought salinity down to 35ppm. Refractometer still reads the same as before.

Definitely trust a calibrated refractometer over that hydrometer.

Swing arm hydrometers can be consistent, but you need to know how far 'off' it is. If you can make a batch of standard, using table salt and RO and a scale, that would tell you.