Salinity in ICP doesn’t match

[AaronFReef]

I just did an ICP test and the results claim a salinity that’s 33.28 ppt.

I’ve been having trouble measuring an accurate salinity for a while because two of my three refractometer calibration solutions (an older Brightwell and a newer BRS) read similar but another read 3 ppt lower. I got a Tropic Marin floating hydrometer to be my absolute reference and it matches the lower solution. My friend also verified towards the lower solution. So I set my salinity to 35.5 ppt based on that hydrometer (just didn’t correct it down the half point before the test) and now the ICP test is claiming I’m still high.

The only thing that would agree with that low salinity reading would be my recalibrated Neptune probe but that jumps a whole point just when I turn off my return so it’s pretty unreliable.

All of this is to give background info for the question: do I trust a Tropic Marin hydrometer or an ATI ICP test where all my other parameters pretty well match targeted levels.

more background: I use brightwell bro marine and only dose BRS two part with occasional magnesium from them too . Nothing else in the last year.

 

[Randy Holmes-Farley]

I'd personally trust the ICP salinity unless I made a salinity standard myself and calibrated the device myself.

 

[AaronFReef]

Hah! Good to know. What do you make of all my parameters being spot on though? Won’t they all be elevated if I add more salt?

 

[vetteguy53081]

Salt should not have an impact based on the amount you would add
Id take a water sample to a trusted LFS and have them test salinity for you to see if their result matches icp or yours

 

[Randy Holmes-Farley]

Hah! Good to know. What do you make of all my parameters being spot on though? Won’t they all be elevated if I add more salt?

Yes, they will rise. Not by that much though. If the new salt water matched the tank, and you went from 33 to 35 ppt, everything will rise by a factor of 35/33 = 1.06.

So 7 dKH becomes 7.4 dKH.

 

[DeputyDog95]

I'd personally trust the ICP salinity unless I made a salinity standard myself and calibrated the device myself.

So, my ICP testing has been consistently showing salinity results at 2ppt lower than what I'm reading.

I am measuring salinity with two devices... Milwaukee digital refractometer and a BRS refractometer. I calibrated the BRS unit with BRS refracto juice (Brightwell product) and it reads 35ppt with the BRS solution and zero with distilled water. The Milwaukee unit reads 35ppt using the BRS solution and zero with distilled water.

I've also made your DIY refractometer solution and both the Milwaukee and the BRS devices read 35ppt.

However, my Hanna conductivity pen marries up with the ICP coming in at 2ppt lower than on my other devices using the reference solution. When I was managing my salinity with the Hanna pen, it lined up pretty closely with the ICP.

Now I'm not sure what to believe.

Thoughts?

 

[Uncle99]

Same here, ICP always a few points lower than my tests.
I just go with the majority, my refractometer and my swing arm say 1.0265…..having no issues….so that’s going to be my target.

 

[Randy Holmes-Farley]

So, my ICP testing has been consistently showing salinity results at 2ppt lower than what I'm reading.

I am measuring salinity with two devices... Milwaukee digital refractometer and a BRS refractometer. I calibrated the BRS unit with BRS refracto juice (Brightwell product) and it reads 35ppt with the BRS solution and zero with distilled water. The Milwaukee unit reads 35ppt using the BRS solution and zero with distilled water.

I've also made your DIY refractometer solution and both the Milwaukee and the BRS devices read 35ppt.

However, my Hanna conductivity pen marries up with the ICP coming in at 2ppt lower than on my other devices using the reference solution. When I was managing my salinity with the Hanna pen, it lined up pretty closely with the ICP.

Now I'm not sure what to believe.

Thoughts?

I don’t know what the issue is, but if icp sodium and chloride are off by 5%, that could explain the results.

 

[Cory]

Measure freshly mixed saltwater and see what the calcium/alk is. Manufacturers will tell you what thier values are based on the salinity. Instant ocean for example should be 380ppm calcium and 10-11dkh.

 

[DeputyDog95]

Same here, ICP always a few points lower than my tests.
I just go with the majority, my refractometer and my swing arm say 1.0265…..having no issues….so that’s going to be my target.

I think I'll do the same. Since I can't ICP my tank weekly or my water change mixes, I need to use the tools I have on hand which appear to be agreeing with each other using different samples.

I just bought a VeeGee refractometer as well, but I need to try and chill my office down to 68 to calibrate it using distilled water per the directions. Not an easy task in FL this time of year. I figure if the 3 agree with each other and the ICP is odd man out, then I'll just ignore the ICP.

 

[DeputyDog95]

I don’t know what the issue is, but if icp sodium and chloride are off by 5%, that could explain the results.

The guy who owns the company is a friend of mine. Very bright guy who is hyper particular about running and maintaining the equipment.

I've discussed the salinity variance with him quite a bit. I finally asked him that if I'm using some of the more popular hobby grade equipment that most of his customers are likely using as well, then does he routinely see lower numbers than 35ppt. Which he confirmed a lot of the tanks he tests for have similar low readings like mine.

I'm still not sure what results to put my confidence in but you're right, if those readings on his equipment are a smidge off, that would explain it.