Apex salinity probe calibration by Randy recipe but still fault readings?

[Trueruby]

Hi everyone,

I am in hobby around 8 years but pretty new to apex neptune systems. So, just got my set including ph, orp, salinity and temp probe.
For salinity probe I used @Randy Holmes-Farley condutivity calibration solution by table salt. Which is supposed to be 53 ms/cm S:35. I let the solution stay in a tank for a while to set temperature at 77F as tank. After calibrating, the salinity probe reads the solution 34.9 PPT which i think not bad!
But when I place probe in to tank( slightly shaking to not have air bubbles) , it reads 31.7 ppt. When I check with refractometer I can see my tank has 33 PPT.
So which one should I trust in this case?

 

[Miami Reef]

Hi everyone,

I am in hobby around 8 years but pretty new to apex neptune systems. So, just got my set including ph, orp, salinity and temp probe.
For salinity probe I used @Randy Holmes-Farley condutivity calibration solution by table salt. Which is supposed to be 53 ms/cm S:35. I let the solution stay in a tank for a while to set temperature at 77F as tank. After calibrating, the salinity probe reads the solution 34.9 PPT which i think not bad!
But when I place probe in to tank( slightly shaking to not have air bubbles) , it reads 31.7 ppt. When I check with refractometer I can see my tank has 33 PPT.
So which one should I trust in this case?

Can you make Randy’s refractometer calibration
solution?

This 3.65 weight percent sodium chloride solution can be made by dissolving 3.65 grams of sodium chloride in 96.35 grams (mL) of purified freshwater.

For a rougher measurement in the absence of an accurate water volume or weight measurement:”

1. Measure ¼ cup of Morton's Iodized Salt (about 73.1 g)
2. Add 1 teaspoon of salt (making about 79.3 g total salt)
3. Measure the full volume of a plastic 2-L Coke or Diet Coke bottle filled with purified freshwater (about 2104.4 g)
4. Dissolve the total salt (79.3 g) in the total water volume (2104 g) to make an approximately 3.65 weight percent solution of NaCl. The volume of this solution will be slightly larger than the Coke bottle, so dissolve it in another container.
[[Notice added post-publication: the standards described here that use Coke bottles are subject to variation in the volume of a 2-L Coke bottle. It has recently come to my attention that such 2-L bottles can vary in total volume, and that this can lead to at least a 1 ppt error in the salinity of the standards matched to seawater salinity of 35 ppt. Standards made with accurate measurements of salt and water should still accurately match 35 ppt.]]

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

 

[Trueruby]

Can you make Randy’s refractometer calibration
solution?

This 3.65 weight percent sodium chloride solution can be made by dissolving 3.65 grams of sodium chloride in 96.35 grams (mL) of purified freshwater.

For a rougher measurement in the absence of an accurate water volume or weight measurement:”

1. Measure ¼ cup of Morton's Iodized Salt (about 73.1 g)
2. Add 1 teaspoon of salt (making about 79.3 g total salt)
3. Measure the full volume of a plastic 2-L Coke or Diet Coke bottle filled with purified freshwater (about 2104.4 g)
4. Dissolve the total salt (79.3 g) in the total water volume (2104 g) to make an approximately 3.65 weight percent solution of NaCl. The volume of this solution will be slightly larger than the Coke bottle, so dissolve it in another container.
[[Notice added post-publication: the standards described here that use Coke bottles are subject to variation in the volume of a 2-L Coke bottle. It has recently come to my attention that such 2-L bottles can vary in total volume, and that this can lead to at least a 1 ppt error in the salinity of the standards matched to seawater salinity of 35 ppt. Standards made with accurate measurements of salt and water should still accurately match 35 ppt.]]

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

Yes I can, I did it actually and it was reading well with refractometer. Really tough situation

 

[ColoredRock]

Read thru this pot and see if it helps you any.

New to Apex

I’m wondering if my salinity probe can mrs pre calibrated. I have three separate salinity testers and they all read 35 ppt and the apex is reading 28. How can I correct this. Thank for helping out!

www.reef2reef.com

 

[Randy Holmes-Farley]

Taken together, the errors for a 31.7 ppt reading on one device and a 33 ppt reading on a second device probably overlap and I’d just conclude the salinity is in the range of those values.

 

[Trueruby]

Read thru this pot and see if it helps you any.

New to Apex

I’m wondering if my salinity probe can mrs pre calibrated. I have three separate salinity testers and they all read 35 ppt and the apex is reading 28. How can I correct this. Thank for helping out!

www.reef2reef.com

Read already thanks for this.

 

[Trueruby]

Taken together, the errors for a 31.7 ppt reading on one device and a 33 ppt reading on a second device probably overlap and I’d just conclude the salinity is in the range of those values.

I agree for sure, retried your refracto solution by preparing with 5 digit sensitive weight measurement. When solution shows 35 ppt on refracto, the tank shows 33 ppt. Mean while salinity probe was showing 32 ppt. So I assume around 32.5 like you are saying. By playing with TC value on salinity probe calibration, I made it sat at 32.7, now feel more confident.