Salinity - Refractometer or Apex Probe

[Privateye]

It's also a matter of what your refractometer is made for. There are ones for seawater, brewing, etc. I think I use a brewing one at the moment, but it was a gift bought off Amazon a decade ago so I'm not certain. If I calibrate to 0 with RO/DI it will be off by a couple ppt when reading in the 30's (according to the Red Sea one I inherited later). Just something I have to account for mentally. The slope of the readings is how they differ.

 

[mpoletiek]

It's also a matter of what your refractometer is made for. There are ones for seawater, brewing, etc. I think I use a brewing one at the moment, but it was a gift bought off Amazon a decade ago so I'm not certain. If I calibrate to 0 with RO/DI it will be off by a couple ppt when reading in the 30's (according to the Red Sea one I inherited later). Just something I have to account for mentally. The slope of the readings is how they differ.

Holy cow. That's some information I wasn't expecting.

 

[mpoletiek]

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.

Makes sense. Thanks!

 

[gbroadbridge]

I bought some solution already. Great resource though.

The problem is that purchased calibration solutions are notoriously unreliable.

It takes only a tiny amount of evaporation from a 100ml bottle to make it useless.

if you spend the money on a good set of scales you can make gallons of calibration fluids for a few cents whenever you feel like it.

 

[rtparty]

Conductivity is the most accurate way to test salinity. Wish I could find Randy's explanation again. The problem isn't the Neptune probe but the technology and implementation on our tanks

 

[gbroadbridge]

Conductivity is the most accurate way to test salinity. Wish I could find Randy's explanation again. The problem isn't the Neptune probe but the technology and implementation on our tanks

This is true, The problem is that temperature compensation is tricky to get right.

Even some well respected manufacturers of aquarium control systems seem to do it their own way, which means the reading can vary between different control systems.

Not sure why, the science is reasonably simple, it is different interpretations that cause problems.

 

[Randy Holmes-Farley]

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?

As I stated above, both of these devices attempt to correct for temperature complications. The swing arm hydrometers I tested were actually better at getting the temperature correction correct then they were in absolute salinity determination.

As an aside, salinity does not change with temperature, only the physical properties tested by these devices changes.

 

[Randy Holmes-Farley]

This is true, The problem is that temperature compensation is tricky to get right.

Even some well respected manufacturers of aquarium control systems seem to do it their own way, which means the reading can vary between different control systems.

Not sure why, the science is reasonably simple, it is different interpretations that cause problems.

Ive never understood the problem either. The exact change in seawater conductivity with temp is well known.

 

[brandon429]

MPoltiek


my hydrometer hasn't drifted in accuracy since I bought the second one to check it ten years ago.

Unless we need to keep basket stars, why pay over twelve bucks to measure salinity/ alert needs I can understand as complex ato setups have serious fail point analysis needs.

I didn't want it to sound like a hydrometer is a ticking time bomb, apparently if I keep rinsing mine in distilled water after every use it'll go another decade at minimum

My swingarm doesn't exactly match a calibrated refractometer, it runs .001 too low, but it's held that mark for years on end reliably without wild variance. When I read of 25 posts regarding bad calibration fluid=refract misread=someone sets their display salinity wrong- a thumped swingarm never did that I recall.

A person who effectively rids bubbles off a testing swingarm sure has one long term consistent salt measure ability

 

[melonheadorion]

i would trust your refractometer more than the apex. the reason being, is that it has less factors that could cause a bad reading, whereas the apex is affected by a couple things. stray voltage near the wire for the probe could cause it to read incorretly, just to name one. i mainly just use my apex probe to see if there are any crazy fluctuations that would indicate a problem. other than that, if i want to confirm what my probe is telling me, i always get out the refractometer. the refractometer shows a difference between the two every time.

 

[gbroadbridge]

MPoltiek


my hydrometer hasn't drifted in accuracy since I bought the second one to check it ten years ago.

Unless we need to keep basket stars, why pay over twelve bucks to measure salinity/ alert needs I can understand as complex ato setups have serious fail point analysis needs.

I didn't want it to sound like a hydrometer is a ticking time bomb, apparently if I keep rinsing mine in distilled water after every use it'll go another decade at minimum

My swingarm doesn't exactly match a calibrated refractometer, it runs .001 too low, but it's held that mark for years on end reliably without wild variance. When I read of 25 posts regarding bad calibration fluid=refract misread=someone sets their display salinity wrong- a thumped swingarm never did that I recall.

A person who effectively rids bubbles off a testing swingarm sure has one long term consistent salt measure ability

Perhaps they are both wrong. Lol

 

[gbroadbridge]

i would trust your refractometer more than the apex. the reason being, is that it has less factors that could cause a bad reading, whereas the apex is affected by a couple things. stray voltage near the wire for the probe could cause it to read incorretly, just to name one. i mainly just use my apex probe to see if there are any crazy fluctuations that would indicate a problem. other than that, if i want to confirm what my probe is telling me, i always get out the refractometer. the refractometer shows a difference between the two every time.

Beg to differ.

I trust my EC probe absolutely.

It does not drift, does not get bubble mania causing false readings, and is calibrated once a month using a DIY solution.

It is never wrong when checked against a reference solution.

The important consideration is that these instruments require care in their use.

They are not simple plug and play devices.

They need to be kept clean, the temperature probe must also be kept clean. They both need to be calibrated and compared to a reference standard. Both the EC probe and the temperature probe must be next to each other.

This is basic laboratory technique, not plug and play.

As much as I like how technology is making things simpler, in some cases it means that things have been dumbed down to the extent that the measurement instrument is being blamed for measurement errors that really are the fault of the user.

 

[mpoletiek]

The problem is that purchased calibration solutions are notoriously unreliable.

It takes only a tiny amount of evaporation from a 100ml bottle to make it useless.

if you spend the money on a good set of scales you can make gallons of calibration fluids for a few cents whenever you feel like it.

Good point.

 

[mpoletiek]

i would trust your refractometer more than the apex. the reason being, is that it has less factors that could cause a bad reading, whereas the apex is affected by a couple things. stray voltage near the wire for the probe could cause it to read incorretly, just to name one. i mainly just use my apex probe to see if there are any crazy fluctuations that would indicate a problem. other than that, if i want to confirm what my probe is telling me, i always get out the refractometer. the refractometer shows a difference between the two every time.

This is the direction I'm leaning.

 

[mpoletiek]

MPoltiek


my hydrometer hasn't drifted in accuracy since I bought the second one to check it ten years ago.

Unless we need to keep basket stars, why pay over twelve bucks to measure salinity/ alert needs I can understand as complex ato setups have serious fail point analysis needs.

I didn't want it to sound like a hydrometer is a ticking time bomb, apparently if I keep rinsing mine in distilled water after every use it'll go another decade at minimum

My swingarm doesn't exactly match a calibrated refractometer, it runs .001 too low, but it's held that mark for years on end reliably without wild variance. When I read of 25 posts regarding bad calibration fluid=refract misread=someone sets their display salinity wrong- a thumped swingarm never did that I recall.

A person who effectively rids bubbles off a testing swingarm sure has one long term consistent salt measure ability

I don't own a hydrometer.

 

[Randy Holmes-Farley]

I don't own a hydrometer.

Sorry, my fault for bringing swing arm hydrometers into the conversation.

 

[mpoletiek]

Sorry, my fault for bringing swing arm hydrometers into the conversation.

LOL! All good.

I think I have a solid strategy now. Appreciate all the responses.

 

[vtecintegra]

Recently learned my lesson using calibration fluid and a refractometer. My ICP came back at 32 ppt instead of 35 ppt. I bought the TM hydrometer and it was 32 ppt. I calibrate the refractometer off of the hydrometer now.

 

[mpoletiek]

Recently learned my lesson using calibration fluid and a refractometer. My ICP came back at 32 ppt instead of 35 ppt. I bought the TM hydrometer and it was 32 ppt. I calibrate the refractometer off of the hydrometer now.

This thing?

 

[vtecintegra]

All I see is an A for Amazon. Here it is.

https://www.bulkreefsupply.com/high-precision-hydrometer-tropic-marin.html