Calibration of a Refractometer

[Shep]

So today I was at my LFS and as I was checking out the owner tried to get me to buy some calibration solution for my refractometer, when I told him that I just use RO/DI water he said that RO/RI water is not good to use and can cause calibration errors. Any truth to this or was he just trying to get me to spend more money?

 

[Rob.D]

Refractometers should only be calibrated to 35 ppt not -0- Randy has a table salt recipe for a calibration solution but store bought is much simpler.

 

[xbrl001]

So today I was at my LFS and as I was checking out the owner tried to get me to buy some calibration solution for my refractometer, when I told him that I just use RO/DI water he said that RO/RI water is not good to use and can cause calibration errors. Any truth to this or was he just trying to get me to spend more money?

I literally just went through this. Used DI to calibrate as zero. Then bought salt water and asked what they keep the level at. Brought it home and tested and it was dead on with what they said.

 

[maxxin69]

Kinda. It will calibrate it, but it will be calibrated with a greater degree of accuracy towards the 1.000 area of the refractometer, which isn't ideal since you will be using it in the 1.023-1.025 range. Here is one story of a reefer that was calibrating his refractometer with RO/DI water.

 

[sucker]

my refractometer instruction says use ro/di

 

[rprew]

I have used both with good results

 

[Rob.D]

http://www.reefkeeping.com/issues/2004-06/rhf/

 

[ssdawood]

If it is a true sea water refractometer like veegee, sine etc then it will read correct for Rodi and 35 ppt even when calibrated to 0 with rodi.

If it's not then the slope will be off resulting in wrong reading for 35 ppt when calibrated with rodi.

 

[CubanHogFish]

I bought my refractometer from BRS and there instruction said to calibrate with solution they provided me with, the solution is 1.026sg which it equals to 35ppt i called them to make sure i understood that correctly and they said yes the reason for that is that the adjustment screw eventually will get stuck and you will no longer be able to calibrate it and also has temperature compensation so it doesn't matter at what temp you take reading it will be correct

 

[tjgr34]

I usually calibrate with RO/DI and then check with saltwater. Just mix a gallon or two of water using the directions on your salt container, and then use the stated salinity level to check the refractometer.

 

[UABsleeper]

I have thought about this a few different times.. And not saying I'm right at all but from my point of view IMO i don't think it's necessary in my aquarium to calibrate it to an exact number using a calibration fluid.. 1 how do I know with 100% confidence that what the manufactures list is completely accurate and 2 my primary goal in checking the salinity in my aquarium is to maintain consistency! I calibrate mine with quality RO/DI from my lfs which is where i buy the majority of my corals and saltwater from! They typically Keep their sg/salinity ~1.024/33ppt according to my refractometer.. And have great success So for my purposes of keeping my salinity consistent at that level with my ato regardless its .01 or so off works well!

 

[xbrl001]

I have thought about this a few different times.. And not saying I'm right at all but from my point of view IMO i don't think it's necessary in my aquarium to calibrate it to an exact number using a calibration fluid.. 1 how do I know with 100% confidence that what the manufactures list is completely accurate and 2 my primary goal in checking the salinity in my aquarium is to maintain consistency! I calibrate mine with quality RO/DI from my lfs which is where i buy the majority of my corals and saltwater from! They typically Keep their sg/salinity ~1.024/33ppt according to my refractometer.. And have great success So for my purposes of keeping my salinity consistent at that level with my ato regardless its .01 or so off works well!

^x2 on the consistency principal...saltwater or RO/DI water isn't going to ruin/affect the surface of the refratometer.

 

[that Reef Guy]

Kinda. It will calibrate it, but it will be calibrated with a greater degree of accuracy towards the 1.000 area of the refractometer, which isn't ideal since you will be using it in the 1.023-1.025 range. Here is one story of a reefer that was calibrating his refractometer with RO/DI water.

I have talked to many people with various problems.

First Questions I ask is "What are you using to test Salinity".

Many people did the same thing and their Salinity was off by 0.04

When using a Refractometer and RO I make sure it says 1.030 which is actually 1.026

Otherwise use the Solution.

I recommend the Glass Bobbing type Hydrometers as they are Lab Grade and the Most Accurate when Testing Salinity.

You do not have to Calibrate them either.

Never use the Plastic Swing Arm Hydrometers as they are always off.

P.S. Refractometers are Temperature Sensitive so your Water Temp could make the Reading Wrong as well.

 

[that Reef Guy]

my refractometer instruction says use ro/di

So does mine.

It is Wrong.

 

[Downbeach]

You should be using a calibration solution that is near the refractive index of the sample you will be testing. So, a 35ppt (1.0264) solution would be best. Here is Randy's article on the subject.

 

[saltyphish]

I use the calibration solution simply because I am calibrating close to what my expected measurement is. Seems to me that will help eliminate any error. Also Make sure to replace your calibration fluid once a year or so. Evaporation can change the value. I am not sure that would really be much of a problem since I always place the cap back on immediately but the solution is less than $10. I plan on switching to a Milwaukee digital tester soon though and will probably still use the solution as a base measurement.

 

[Shep]

So it would be a good investment to pick up?

 

[saltyphish]

I believe so. Doesn't make it right but it makes sense to me so I do it. I have tested my ro/di water after suing the solution and measured right on as well.

 

[Downbeach]

So it would be a good investment to pick up?

Yes, you will find it important when/if you need to start dosing. Consistency is important, but if you keep a low SG, your Ca, Mg and Alk will also follow, since you are adding those elements with your WC's.

 

[underwaterdan]

How often do you guys calibrate ?