How accurate is the ATI ICP test?

[bluecheese]

I sent my water samples to ATI two weeks ago. I just received my results. Most parameters were where I thought they should be. Except salinity. ATI is showing my salinity at 31.27 PSU, which is very low. I check my salinity weekly with a BRS refractometer. The refractometer is calibrated at least monthly with BRS Refracto Juice. I just calibrated it this morning after receiving the results, and my tank's water is still showing at 35ppm.

So either my refractometer is faulty and BRS's Refracto Juice is not at the 35 it claims, or ATI is wrong.

I'm using Instant Ocean Reef Crystals salt. I mix it at their recommended 1/2 per 5 gallons.

I'm not really sure where to go from here, other than bringing a water sample to my LFS to be tested.

 

[Snoopy 67]

A double check sounds like a good idea.
Unless you weigh the ingredients there is always a chance of error.
And yes, the calibration solution could have changed slightly.

 

[bluecheese]

So, I posted this question on the AskBRS facebook page. They declined my post, but responded with

If mineral levels are in expected range, corals look happy and not stressed, and if you take a sample to the LFS and get comparable results I wouldn't worry too much on the ATI salinity. Accuracy will depend on the method use by them

So I guess my next step will be taking the water to my LFS to get tested.

 

[exnisstech]

Not sure what 1/2 per 5 gallons means. I've been using IO and reef crystal for years and always have to use more than they recommend. I mix 28 gallons at a time and have to use 16 cups to get to 1.025. Maybe look into a hydrometer as a backup. I recently bought one of the Tropic marine ones just to check my checkers.

 

[fishyjoes]

I would suggest you get a tropic marin high precision hydrometer.

They're easy to read, accurate, and don't need calibration. The downsides are that they're large, need a lot of water to perform the test (a 500ml cylinder), and are easily broken.

My ATI-ICP test and my own salinity measurement matched exactly (1.0258)

 

[areefer01]

I sent my water samples to ATI two weeks ago. I just received my results. Most parameters were where I thought they should be. Except salinity. ATI is showing my salinity at 31.27 PSU, which is very low. I check my salinity weekly with a BRS refractometer. The refractometer is calibrated at least monthly with BRS Refracto Juice. I just calibrated it this morning after receiving the results, and my tank's water is still showing at 35ppm.

So either my refractometer is faulty and BRS's Refracto Juice is not at the 35 it claims, or ATI is wrong.

I'm using Instant Ocean Reef Crystals salt. I mix it at their recommended 1/2 per 5 gallons.

I'm not really sure where to go from here, other than bringing a water sample to my LFS to be tested.

Maybe you have a typo because Instant Ocean is 1/2 cup to 1 US gallon.

 

[bluecheese]

Sorry. A typo on my part. I use 1/2 cup per every gallon.

 

[Randy Holmes-Farley Verified Community Expert]

Any chance the sample froze? If filled all the way, Oceamo has shown errors when liquid is forced out of the vials, which would lower salinity once the ice melts.

 

[drolmaeye]

I experienced exactly what the OP describes -- faithfully calibrating my BRS hydrometer with the BRS calibration solution, mixing to 35 ppt, and getting an ATI-ICP test result of 31-32 PSU. As others suggested above, I purchased a Tropic Marin hydrometer to double-check my results and the hydrometer measurement was lower than I was expecting, and closer to the value from the ICP test. I have since bumped up my salinity so the Tropic Marin measurement comes back between 1.026 and 1.027 (I still use analog or digital refractometer most of the time for mixing and quick checks).

One hint was my major elements seemed to be a bit low based on more than one salt manufacturer's target parameters.

 

[ReeferHD]

i'd check with a swing arm hydrometer as they are very consistent and don't need calibration.

 

[bluecheese]

Any chance the sample froze? If filled all the way, Oceamo has shown errors when liquid is forced out of the vials, which would lower salinity once the ice melts.

Sample came from south Louisiana, so it wouldn't have frozen on my end. Between here and Germany, I couldn't say.

 

[exnisstech]

I don't understand how you folks are able to use 1/2 cup IO to 1 gallon of RODI. I've been using IO for 8 years and always have to add 32 1/2 cups to 28 gallons of RODI

 

[taricha]

different trusted calibration solutions giving different answers is exactly the scenario in which I'd consult Randy's article about making salinity standards.

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