Salinity - Refractometer or Apex Probe

[mpoletiek]

So I'm learning about salinity and how temperature impacts specific gravity, which is measured by my refractometer?

Anyways, I achieved 1.026 on the display tank with a temp bouncing between 78-79 when measured with the refractometer.

However, my apex probe never comes close to that value, hovering around 32.3(ppm?).

At this point I'm thinking I should just use the refractometer as the accurate measure and the probe as an indicator of change.

Am I thinking about this right? Does anyone else trust the refractometer over the conductivity probe?

Thanks,

 

[HomebroodExotics]

Is your refractometer calibrated?

 

[Randy Holmes-Farley Verified Community Expert]

One cannot tell which is more accurate from a different measurement result.

Both devices try to correct for temperature issues.

 

[PeterC99]

Get your saltwater tested at LFS. Then you will have a better idea which is more accurate.

 

[mpoletiek]

Both probe and refractometer are calibrated.

Temp impacts refractometer which is just a looking glass.

Temp shouldn't impact the apex probe because it accounts for that?

 

[mpoletiek]

Actually I just read somewhere that calibrating a refractometer with RO/DI water will get it reading a point or two higher?

If thats true, then that explains the mystery. The apex probe was calibrated with solution, while the refractometer was calibrated with RO/DI water.

 

[killer2001]

Mine was reading low until I had to re-calibrate it with temperature compensation. I don't think its enabled by default. I have my TC Factor % set to 2.1 I believe. It's in the advanced tab in the salinity probe configuration.

 

[mpoletiek]

Mine was reading low until I had to re-calibrate it with temperature compensation. I don't think its enabled by default. I have my TC Factor % set to 2.1 I believe. It's in the advanced tab in the salinity probe configuration.

I'm reading this as you trust your refractometer and adjust your probe's calibration. This is a valid strategy as far as I'm concerned, but how do we calibrate our refractometers?

Do we use RO/DI water or specific calibration solution?

Thanks,

 

[mpoletiek]

I should probably add I'm using the portable refractometer you calibrate with a screw. I stay on top of keeping that thing calibrated. I check it all the time, but I always use RO/DI water.

 

[rtparty]

General rule is to always calibrate to whatever you are testing. We aren't testing RO water with our refractometers. We are trying to test for 35ppt. Therefore, we should calibrate with a solution known to be 35ppt.

 

[mpoletiek]

General rule is to always calibrate to whatever you are testing. We aren't testing RO water with our refractometers. We are trying to test for 35ppt. Therefore, we should calibrate with a solution known to be 35ppt.

This makes sense too. I guess I'll try calibrating with some solution and go from there.

 

[Roli's Reef Ranch]

So I'm learning about salinity and how temperature impacts specific gravity, which is measured by my refractometer?

Anyways, I achieved 1.026 on the display tank with a temp bouncing between 78-79 when measured with the refractometer.

However, my apex probe never comes close to that value, hovering around 32.3(ppm?).

At this point I'm thinking I should just use the refractometer as the accurate measure and the probe as an indicator of change.

Am I thinking about this right? Does anyone else trust the refractometer over the conductivity probe?

Thanks,

Neither, get a tropic Marin Hydrometer (the only one I trust) and a Hanna salinity checker for ease of use and for backup. I've gone down that route and crashed tanks like a DA due to faulty readings due to my fault. I prefer devices that don't need to be calibrated, or calibrated infrequently.

 

[gbroadbridge]

This makes sense too. I guess I'll try calibrating with some solution and go from there

Make you own reference solution as explained in the article below, and calibrate to that.

There are recipes for refracs and EC probes in the article.

https://reefkeeping.com/issues/2004-06/rhf/index.php

 

[Roli's Reef Ranch]

This makes sense too. I guess I'll try calibrating with some solution and go from there.

If you want to play that game you can buy a refractometer calibration solution which is supposed to be 35 ppt/1.026 SG. The APEX probe is fairly useless and unreliable IMO. There are multiple threads on this piece of "gear." It's overkill for something you don't need to check very often. The less gear, the simpler the system, and the fewer points of failure. Send it back to BRS or wherever you got it from and get 3 T/Marin hydrometers. Break the first two and use the 3rd!

 

[KStatefan]

So I'm learning about salinity and how temperature impacts specific gravity, which is measured by my refractometer?

Your refractometer is reading the refractive index not specific gravity.

Here is a good article written by Randy

http://reefkeeping.com/issues/2006-12/rhf/index.php

 

[mpoletiek]

Neither, get a tropic Marin Hydrometer (the only one I trust) and a Hanna salinity checker for ease of use and for backup. I've gone down that route and crashed tanks like a DA due to faulty readings due to my fault. I prefer devices that don't need to be calibrated, or calibrated infrequently.

Great strategy.

 

[mpoletiek]

Make you own reference solution as explained in the article below, and calibrate to that.

There are recipes for refracs and EC probes in the article.

https://reefkeeping.com/issues/2004-06/rhf/index.php

I bought some solution already. Great resource though.

 

[mpoletiek]

Your refractometer is reading the refractive index not specific gravity.

Here is a good article written by Randy

http://reefkeeping.com/issues/2006-12/rhf/index.php

Right. Thanks for clarifying.

 

[Jubei2006]

When you calibrate a refractometer, use calibration fluid at the stated temp (usually reef temp). Throw the bottle in your sump to get it to your tanks temp (most say 1.025 or .026 at 26 degrees celcius which is tank temp), and calibrate from there. I use a profilux 4 with conductivity, but I spot check 1 to 2 times weekly with my refractometer to verify it's not drifting. So my profilux 4 says 53.7 mS conductivity at 80 degrees right now which is just above 1.026 which is what my calibrated refractometer says. So probe is good and all is right with the my world.

 

[X-37B]

Great strategy.

After 30+ hobby years the TM is all I will use.