Refractometer Temperature Compensation

[SeansNanoReef]

Hey there,

I'm using one of those basic refractometers that claim to adjust their scale based on ambient/sample temperatures (ATC). I've found that it holds calibration extremely well, but I still check it every other test.

One thing I haven't seen being discussed is my particular method of calibrating. I set my tank at 77F (checked with multiple thermometers) and float the calibration solution AND the refractometer prism (where the sample is placed) to bring them both to the same temp.

Most people say to just float the solution, put it on the prism, and wait 30 seconds for the temp to 'stabilize' before reading. However, this doesn't make much sense to me, as if ambient temperatures are several degrees cooler than the sample water (~68F in my case) the water will cool below the target 77F. A couple drops of water won't bring the prism and surrounding aluminum to 77 degrees.

In my experience, my method and the "wait 30 seconds" method provides different results - floating the prism to temp makes the reading about 1 PPT lower as I expect. Does this mean the ATC actually isn't that accurate?

So, which method would be best? I don't have a true glass hydrometer to test this with. I think by ensuring both the refractometer and the solution are both at 77F, it would be closer to a TRUE 77 degrees rather than somewhere between room temp and 77.

 

[exnisstech]

I use a TM hydrometer to test fresh mixed water at 77 degrees adjusted to 1.025 salinty then use that same water to calibrate my refractometers.
I've tested salt water at around 60 degrees using a ATC refractometer which is what my basement temp is and again when the water is warmed up and I get the same reading at both temps so I'm not sure warming everything up is necessary but I suppose it can't hurt.

 

[SeansNanoReef]

Interesting, sometimes I get up to a 2 ppt difference with mine. Maybe my ATC function is defective or something.

 

[fish_collector]

Your salinity isn’t critical enough to have to go through all of that. Somewhere near 35 ppt as measured with your refractometer is good.

For 20 years I used an instant ocean swing arm to measure salinity, it worked. Nowadays everyone fusses over how to really measure it, but in the end it’s not that critical.

If you are in need of a true hyposalinity treatment where the salinity is just barely enough to not kill your fish but eradicate a pathogen, then yes it may be important to be able to measure it accurately, but otherwise just roll with what your refractometer says on the fly and don’t sweat it, it’s good enough.

FWIW, I’ve compared my cheap Amazon refractometer with my buddies $350 Milwaukee unit and they read exactly the same. I’ve never messed with the adjusting screw.

 

[SeansNanoReef]

I totally agree, one doesn't really need to know exactly what their salinity is. I'm being a little critical of it now because I was using one of those conductivity style pens that turned out to be completely inaccurate even when calibrated, and I was dealing with mysterious invert deaths for a little while. Turns out my salinity was actually 40ppt. That left a bad taste so I guess I'm going a bit overboard with my attention to salinity, specifically accuracy.

 

[fish_collector]

Ok fair enough. The Topic Marin hydrometer that exnisstech referred to is the gold standard for something to compare to. I understand your position with it all, 40 probably wasn’t high enough to kill things though. I’ve let my ATO go dry and end up with 40 in my SPS tank, and the only reason I checked the salinity was to find out how much fresh water I had to add

 

[Patx]

I use a TM hydrometer to test fresh mixed water at 77 degrees adjusted to 1.025 salinty then use that same water to calibrate my refractometers.

This, this and this !

 

[SeansNanoReef]

Ok fair enough. The Topic Marin hydrometer that exnisstech referred to is the gold standard for something to compare to. I understand your position with it all, 40 probably wasn’t high enough to kill things though. I’ve let my ATO go dry and end up with 40 in my SPS tank, and the only reason I checked the salinity was to find out how much fresh water I had to add

Yeah, I didn't have any issues with my fish or corals, just snails...I think it was because every other element was also through the roof due to my particular salt, and I didn't "acclimate." As soon as I lowered my salinity they have been doing great.

 

[Randy Holmes-Farley]

Hey there,

I'm using one of those basic refractometers that claim to adjust their scale based on ambient/sample temperatures (ATC). I've found that it holds calibration extremely well, but I still check it every other test.

One thing I haven't seen being discussed is my particular method of calibrating. I set my tank at 77F (checked with multiple thermometers) and float the calibration solution AND the refractometer prism (where the sample is placed) to bring them both to the same temp.

Most people say to just float the solution, put it on the prism, and wait 30 seconds for the temp to 'stabilize' before reading. However, this doesn't make much sense to me, as if ambient temperatures are several degrees cooler than the sample water (~68F in my case) the water will cool below the target 77F. A couple drops of water won't bring the prism and surrounding aluminum to 77 degrees.

In my experience, my method and the "wait 30 seconds" method provides different results - floating the prism to temp makes the reading about 1 PPT lower as I expect. Does this mean the ATC actually isn't that accurate?

So, which method would be best? I don't have a true glass hydrometer to test this with. I think by ensuring both the refractometer and the solution are both at 77F, it would be closer to a TRUE 77 degrees rather than somewhere between room temp and 77.

With an ATC refractometer, the temp of a standard and the temp
Of the sample should not matter, at least within its range of ATC effectiveness. If you do see temp differences, then yes, it means the correction is not perfect and having tank and 35 ppt standard at close to the same temp is best.

Realize that drops on the refractometer fairly quickly come to the temp of the refractometer, not the starting water temp.

 

[Randy Holmes-Farley]

Ok fair enough. The Topic Marin hydrometer that exnisstech referred to is the gold standard for something to compare to. I understand your position with it all, 40 probably wasn’t high enough to kill things though. I’ve let my ATO go dry and end up with 40 in my SPS tank, and the only reason I checked the salinity was to find out how much fresh water I had to add

Just to clarify, it may be very convenient and perfectly adequate for reefers to do that, but it is not meeting the definition of a gold standard. Conductivity is truly the gold standard,,and is how salinity is actually defined these days.

 

[rtparty]

Salinity is absolutely essential and the most important parameter to get correct. All elements are predicated upon a correct salinity to begin with.

We see it almost daily. Someone will come on claiming a bad batch of salt because the parameters are super low or super high but the reality is their salinity is wrong.

They will claim their “tank has always run at low levels” but in reality their salinity was incorrect.

Anyone saying otherwise is ignoring basic science

 

[Waters]

I haven't calibrated my refractometer since the day I got it, 4 years ago lol. It still reads identical to my Milwaukee. If either shows something way off, then I will dig a bit further.

 

[BryanM]

Hey there,

I'm using one of those basic refractometers that claim to adjust their scale based on ambient/sample temperatures (ATC). I've found that it holds calibration extremely well, but I still check it every other test.

One thing I haven't seen being discussed is my particular method of calibrating. I set my tank at 77F (checked with multiple thermometers) and float the calibration solution AND the refractometer prism (where the sample is placed) to bring them both to the same temp.

Most people say to just float the solution, put it on the prism, and wait 30 seconds for the temp to 'stabilize' before reading. However, this doesn't make much sense to me, as if ambient temperatures are several degrees cooler than the sample water (~68F in my case) the water will cool below the target 77F. A couple drops of water won't bring the prism and surrounding aluminum to 77 degrees.

In my experience, my method and the "wait 30 seconds" method provides different results - floating the prism to temp makes the reading about 1 PPT lower as I expect. Does this mean the ATC actually isn't that accurate?

So, which method would be best? I don't have a true glass hydrometer to test this with. I think by ensuring both the refractometer and the solution are both at 77F, it would be closer to a TRUE 77 degrees rather than somewhere between room temp and 77.

This is just another reason I switched to the TM Hydrometer. No fussing around.

 

[GSPClown94]

I also have experienced this where the temperature of the actual refractometer changes the reading, I believe this is from something broken within the refractometer related to the automatic temperature control. I would look into getting a new device to measure salinity.

 

[fish_collector]

Just to clarify, it may be very convenient and perfectly adequate for reefers to do that, but it is not meeting the definition of a gold standard. Conductivity is truly the gold standard,,and is how salinity is actually defined these days.

Yes I mean from a hobbyists perspective.

 

[SeansNanoReef]

I'm leaning towards a true seawater refractometer like the VeeGee. I have a small tank so filling a 1000 ml graduated cylinder for a hydrometer every time would be just as big or more of a hassle for my situation.

For now my temperature equalization method seems to be effective, the cheap refractometer hasn't needed any adjustments since purchase.

 

[Randy Holmes-Farley]

Yes I mean from a hobbyists perspective.

It's not worth a debate, and the TM hydrometer is generally a fine instrument that I'm not going to criticize if one validates its accuracy with a standard, but many hobbyists and Reef2Reef members do use high quality instruments to measure conductivity. :)

 

[daikaijureefer]

Just to clarify, it may be very convenient and perfectly adequate for reefers to do that, but it is not meeting the definition of a gold standard. Conductivity is truly the gold standard,,and is how salinity is actually defined these days.

Randy, can you recommend a conductivity probe/ meter that meets these qualifications?

 

[Randy Holmes-Farley]

Randy, can you recommend a conductivity probe/ meter that meets these qualifications?

Since they are quite expensive, many hobbyists get them on ebay.

For decades, I used an Orion Model 128 with a four electrode probe. Many old Orions are good. There are different probe models, and some work in seawater, while others are optimized for lower conductivity. It finally broke and I bought this very old one from VWR on ebay:

Randy's Tank and Learn Thread

can we get a full tank pic please :)

www.reef2reef.com

Rishma bought this meter:

New (to me) toy- conductivity meter

I’m just excited and nobody outside this forum would care 😁

www.reef2reef.com

 

[fish_collector]

It's not worth a debate, and the TM hydrometer is generally a fine instrument that I'm not going to criticize if one validates its accuracy with a standard, but many hobbyists and Reef2Reef members do use high quality instruments to measure conductivity. :)

No debate at all Randy. Thank you for mentioning there was something better.