Refractometer, make sure it's calibrated.

[Dekon]

Been a long time lurker on R2R. Great forum with great information. So, I had an unexplained tank crash earlier this year, could not figure out why. Tank had been going great for 5 years. Lost everything except for a hippo tang, a clown fish, and two snails. After the crash, and many water changes later got my perimeters back in line, but still could not keep any inverts alive, and because of that I was afraid to add anything to the tank. Took my water to my LFS, perimeters tested fine. As an afterthought, he tested my salinity, it was 1.032. I run my tank at 1.024 or so I thought. Refractometer was way off. I never ever thought to check it. Sorry to be so long winded but for new reefers and experienced ones, make sure your refractometer is calibrated. I do it once a month now.

 

[redfishbluefish]

To add to what @Dekon said, calibrate with 53mS fluid (35 ppt, 1.026 sg), and NOT RO/DI water.

 

[Jlobes]

To add to what @Dekon said, calibrate with 53mS fluid (35 ppt, 1.026 sg), and NOT RO/DI water.

agreed! i calibrate my refractometer every time i use it.

 

[Vinh]

Thanks for the reminder! I just re-calibrated and what I thought was 1.025 was actually 1.022. I need to get into a better habit of calibrating more often. Time to top-off with saltwater mix to raise it back up.

 

[AdamNC]

I have a habit of calibrating mine once a week when I check my salinity.

 

[JasReef]

To add to what @Dekon said, calibrate with 53mS fluid (35 ppt, 1.026 sg), and NOT RO/DI water.

I'm curious why you say not to use ro/di water. I thought that was the standard.

I do happen to have 53ms fluid so I will use that to double check. [emoji1]

 

[Jlobes]

I'm curious why you say not to use ro/di water. I thought that was the standard.

I do happen to have 53ms fluid so I will use that to double check. [emoji1]

calibrating with RO is not the best option, as it is quite far away from your expected result.

If you ever use a PH meter, its very similar, they suggest to calibrate close to the range you are testing or do a multi step(high/low) calibration. If you calibrate with RO, thats close to the zero mark, calibrating with 35ppt solution, is more accurate because you are calibrating within the desired range

 

[Tanggirl12]

I check with refractometer and my hydrometer, which run the same.

 

[domination2580]

Well here's a question.....I've been told y even use the calibration fluid? Water has 0 salinity...use fresh water, adjust to zero...I don't believe in that but that's what I've been told...please explain why we use calibration fluid

 

[Jlobes]

look ^^

 

[domination2580]

Well what's the difference between 0 and the certain range? If ro is 0 then it's 0 if it's 35 PPT then it's 35PPT

 

[Randy Holmes-Farley Verified Community Expert]

Well here's a question.....I've been told y even use the calibration fluid? Water has 0 salinity...use fresh water, adjust to zero...I don't believe in that but that's what I've been told...please explain why we use calibration fluid

There are two important reasons.

The first is that most of the refractometers sold to hobbyists are not designed for seawater (they likely are not unless they claim "true seawater refractometer). Seawater has a different relationship between refractive index (which these devices measure) and specific gravity or salinity (which these devices report) than does the brine (sodium chloride) solution they are intended for. So even if perfectly manufactured and perfectly calibrated at 0 salinity, they will give incorrect values for seawater, and are off by an exactly known amount. If you have this type of refractometer, and it was perfectly made and calibrated in freshwater, it will ALWAYS read seawater to be higher in salinity than it actually is (misreporting an actual 33.3 ppt to be 35 ppt).

The second reason is that even if it is a seawater refractometer, calibration at a point (0 ppt) far from your intended use (35 ppt) requires that it be perfectly made. Calibration at 35 ppt and use at 35 ppt requires no such level of perfection in the manufacturing. Even if it is a very crappy refractometer, matching the 35 ppt standard will get you very close to 35 ppt. Calibrating at 0 ppt and then hoping it is calibrated at 35 ppt is just that: hope that it was made right.

Further, it is never going to lead to errors to calibrate with a high quality 35 ppt solution, but it can lead to errors to use RO/DI water.

The only exceptions I know of are certain digital refractometers that , becuase of their electronics, force calibration with RO/DI, but you can always check their performance with a 35 ppt standard.

Also, beware that a 53 mS/cm standard DOES NOT necessarily match the refractive index of 35 ppt seawater unless it is designed to do so. So please check that the standard is claimed for this purpose and not just for calibrating a conductivity meter. The Pinpoint standard is suitable.

This has more on these issues, and gives a DIY calibration recipe:

Refractometers and Salinity Measurement by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2006-12/rhf/index.php

 

[domination2580]

Thank you sir

 

[joeyhatch11]

For the past 4 years all I've used is RO/DI to calibrate my refractometer. I always do 2 passes with the RO/DI making sure its set for 0. Every time making water or just checking my salinity I've always came back with the same result, 1.025. For giggles, I just ordered some calibration solution and will test my tanks against that to see how close if not spot on it is against the RO/DI.

 

[Randy Holmes-Farley Verified Community Expert]

Thank you sir

You're welcome.

 

[Randy Holmes-Farley Verified Community Expert]

For the past 4 years all I've used is RO/DI to calibrate my refractometer. I always do 2 passes with the RO/DI making sure its set for 0. Every time making water or just checking my salinity I've always came back with the same result, 1.025. For giggles, I just ordered some calibration solution and will test my tanks against that to see how close if not spot on it is against the RO/DI.

A perfectly miscalibrated refractometer will also give the same, slightly wrong, result every time.

You can tell whether it is a seawater or brine refractometer in many cases by seeing what specific gravity lines up with 35 ppt. If a specific gravity of 1.0264 lines up with 35 ppt, it is a seawater refractometer. If the specific gravity of about 1.025 lines up with 35 ppt, it is a brine refractometer.

But in general, if you are reading in specific gravity (rather than ppt), the inherent errors in perfect brine refractometers tend to be smaller. When a brine refractometer is perfectly calibrated, it will read the specific gravity of 35 ppt seawater to be a bit low, at 1.0261 instead of about 1.0264. That error (reading 0.0003 or so too low) is, however, probably less than most reef aquarists are concerned with.

 

[Rausch]

I calibrate mine with every water change (once a week), so quick and easy to check. Stability is the key to success. I only really check the water i am putting into the tank though. I will check tank levels every now and then just to be sure everything is staying in the tank

 

[joeyhatch11]

The refractometer I'm using is a Vertex

 

[AdamNC]

Well here's word for word how to calibrate a Red Sea Seawater Refractomer from their instructions and it states to use DI water.

Calibration:

Alignment should always be carried out with the instrument at 22-25°C. Allow the refractometer to stand at this temperature for 30 minutes before alignment.

1. Remove the cover from the alignment screw.
2. Place a sample of DI water on the glass prism and check

the salinity reading as directed above.
3. If the reading is not exactly on the zero ppt mark on the

scale, adjust the position of the reading by rotating the alignment screw with the screwdriver provided until the reading is zero ppt.

4. Replace the cover from the alignment screw.

 

[Randy Holmes-Farley Verified Community Expert]

Well here's word for word how to calibrate a Red Sea Seawater Refractomer from their instructions and it states to use DI water.

Calibration:

Alignment should always be carried out with the instrument at 22-25°C. Allow the refractometer to stand at this temperature for 30 minutes before alignment.

1. Remove the cover from the alignment screw.
2. Place a sample of DI water on the glass prism and check

the salinity reading as directed above.
3. If the reading is not exactly on the zero ppt mark on the

scale, adjust the position of the reading by rotating the alignment screw with the screwdriver provided until the reading is zero ppt.

4. Replace the cover from the alignment screw.

Yes, that is a true seawater refractometer (or at least claims to be), so if it is made perfectly, RO/DI water works perfectly for calibration.

Whether it is made perfectly or not, a 35 ppt seawater standard also works perfectly to calibrate it.

Note that Red Sea specifically says on their web site for this refractometer that most are not this type:

http://www.redseafish.com/red-sea-salts/seawater-refractometer-salinity-test/
from it:

"Most refractometers used within the aquarium hobby are not specifically designed for reef aquariums and use an algorithm for the measurement of brine (NaCl – rather than seawater) and at a temperature of 15oC/59 0F rather than 25oC/77 0F. Thus, a measurement deviation of up to 1.5ppt is possible, which can have a significant adverse effect on coral growth and coloration."