Salinity, Refractor, and Calbration

[oldschoolgoods]

When starting my aquarium I read here I was suppose to calibrate my refractor with a 35PPM solution not RO or distilled and that’s what did. I used Reagents Solution. My tank is thriving and everything is growing and looks happy n healthy. Anyways recently I’ve tested the water in my bags of fish and corals from both stores I frequent. One was 1.030 and the other I believe was 1.028 (I can’t recall to the exact point as I didn’t make a note of that one and it was a little while ago). When I did a test calibration with RO before my solution came mine was about 1.028. I assume I’m doing right calibrating with the solution and I should ignore the stores higher numbers? Mine is coming is at 1.026

 

[RobertK]

Not sure I completely understand your question, but I can tell you:
- it is best to calibrate hobbyist refractometers to a salinity of 35 PPT or SG 1.0264 rather than calibrate to 0 with pure water
- commercially available calibration solutions are not always accurate
- you can make your own calibration solution using the instructions in this article (the section on Refractometer Standard)
- pet shops often keep their saltwater fish in lower SG to save money on salt.
Hope that helps!

 

[slingfox]

I would not trust any off the shelf calibration solution. Better to make your own.

 

[Chris_from_SoCal]

I recently ran into this. 30 years ago refractometers were not adjustable. When I started again I trusted the one I bought and something did not seem right so I purchased a digital meter. At first I thought the digital meter was way off. After a bunch of looking around I found out that the newer refractometers are adjustable.

I watched a few videos on how to calibrate the new refractometer and found that it was way off and my salt was way to high. After adjusting it it now matches my digital one and the tank is doing way better.

 

[JonasRoman]

I have always calibrated to RO water. When I double-check against a professional lab like ICP, the results are similar. Maybe I have been a little fortunate that this exact refractometer have has the correct slope and no issues with manufacturing. As I understand it, the reason for calibrate to marine salt with a known concentration is to compensate for slope variation due to imperfect manufacturing.

 

[winxp_man]

One recommendation from me. Aside of all these calibration needing tools, I would recommend you grab a Tropic Marin hydrometer. Super accurate, and you only need a 500ml graduated cylinder from Amazon, and a temp salinity adjusting link to get salinity correction for temp difference.

I use many other things, but after loosing a flame angel to high salinity spike in new salt, I said never again will I not verify salinity with my hydrometer, when big water changes are done. The flame was in a QT. 15 gallon and did a 10 gal WC which spiked salinity because my digital reader was off.

 

[oldschoolgoods]

Not sure I completely understand your question, but I can tell you:
- it is best to calibrate hobbyist refractometers to a salinity of 35 PPT or SG 1.0264 rather than calibrate to 0 with pure water
- commercially available calibration solutions are not always accurate
- you can make your own calibration solution using the instructions in this article (the section on Refractometer Standard)
- pet shops often keep their saltwater fish in lower SG to save money on salt.
Hope that helps!

I forgot to add the most important part. My salinity reads 1.026 on my refractor. Which match’s the calibration solution I’ve used. Tho the tires waters are both coming in a little higher and that concerns me. Tho everything in mine is thriving.

 

[Fish Fan]

The calibration solution that you buy is likely off. It's best to use a DIY salinity calibration fluid that you can easily make with regular Morton's kitchen salt and a decent kitchen scale or measuring spoons. Use this solution to calibrate your refractometer, then double check your salinity readings:
https://www.reef2reef.com/ams/reef-aquarium-salinity-diy-calibration-standards.956/

Good luck!

 

[Seregus]

I have refractometer with LED from Aquamedic. Digital probe from GHL and digital Milwaukee unit.

All three have different ways of calibrating them.

All three had their own manuals with exact way of calibrating.

After doing calibration refractometer and digital Milwaukee shows exact same number for my water. GHL probe is 1 point lower, but manual says ‘adjust’ in digital settings. After it was done - if salinity rises probe shows it was rised.

So my point is - you need to follow calibration manual which come with your tool. People here have their own tools and their own calibration manuals. Some can be same as yours, some can be different.

As for water from your LFS - were the bags sealed? Maybe some evaporation happened?

 

[Anonymous'Reefer90]

Utilizo un refractómetro Red Sea. En las instrucciones de uso se recomienda calibrarlo con agua RODI. Tiempo después de comprar el refractómetro, adquirí la solución BRS y, sin recalibrarlo, la solución me dio un valor muy similar a 35 PPT.

After that I measured the tank water twice plus one calibrated with the water at zero tds with RODI water and the other calibrated with the BRS solution and they were very, very similar, varying 0.5 PPT.

 

[RobertK]

I have always calibrated to RO water. When I double-check against a professional lab like ICP, the results are similar. Maybe I have been a little fortunate that this exact refractometer have has the correct slope and no issues with manufacturing. As I understand it, the reason for calibrate to marine salt with a known concentration is to compensate for slope variation due to imperfect manufacturing.

I think it depends on the refractometer. Some can be calibrated to zero but my understanding is that in general it is better to calibrate them closer to the range you will be using it at.

One recommendation from me. Aside of all these calibration needing tools, I would recommend you grab a Tropic Marin hydrometer. Super accurate, and you only need a 500ml graduated cylinder from Amazon, and a temp salinity adjusting link to get salinity correction for temp difference.

I use many other things, but after loosing a flame angel to high salinity spike in new salt, I said never again will I not verify salinity with my hydrometer, when big water changes are done. The flame was in a QT. 15 gallon and did a 10 gal WC which spiked salinity because my digital reader was off.

I use both. I did a one time calibration check of the Tropic Marin hydrometer using the specific gravity standard in the above linked article (a different recipe for mixing the calibration solution than for the refractometer) to make sure it was accurate from the factory. I then calibrated the refractometer to match the hydrometer using fresh mixed saltwater. I did also mix up some of the refractometer standard to calibrate the refractometer. It is reassuring when they all give the same results.

 

[Randy Holmes-Farley Verified Community Expert]

. As I understand it, the reason for calibrate to marine salt with a known concentration is to compensate for slope variation due to imperfect manufacturing.

If it’s a true seawater refractometer, that is correct. If it is, as the majority are, a repurposed brine refractometer then even if perfectly made, it has a slope mismatch.

 

[Randy Holmes-Farley Verified Community Expert]

I used Reagents Solution.

I’ve not heard of that. Do you have a link? It may not be what you think it is.

 

[oldschoolgoods]

I’ve not heard of that. Do you have a link? It may not be what you think it is.

https://a.co/d/0hPFzHxa

I found it in an old post on here where I was setting up my aquarium.

I’m hesitant to change as I feel my fish and corals are thriving better in my aquarium than they were in the store as I was waiting on buying some of them. But I have ocd and want everything perfect.

 

[Randy Holmes-Farley Verified Community Expert]

Ok, here’s a tell of a possibly crappy product. The link above says it is 35 ppt and literally on both the label and the advertisement it says it is 53 us/cm. lol

Should be 53 mS/cm.

Having your actual product label (not just an ad typo) off by a factor of 1000 does not inspire any confidence whatsoever.

 

[RobertK]

I have always calibrated to RO water. When I double-check against a professional lab like ICP, the results are similar. Maybe I have been a little fortunate that this exact refractometer have has the correct slope and no issues with manufacturing. As I understand it, the reason for calibrate to marine salt with a known concentration is to compensate for slope variation due to imperfect manufacturing.

What refractometer are you using?

 

[JonasRoman]

What refractometer are you using?

DD