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Over the past 24 hours I have been investigating and testing the Hanna HI98319 salinity tester due to some issues I had noticed on a new batch of salt that I mixed up. I wanted to test out Captiv8 Aquaculture's Formul8 Reef salt and I made up my first batch last night. When I mixed to the instructions for 25gallons of water I was reading low on my salinity through my Hanna salinity tester. I had just guessed on the 25 gallon RODI volume in my 32G brute mixing container though based on dumping in 5 gallon buckets of water, so I recalibrated my salinity tester and confirmed the salinity value and added salt up till I reached the 35.4 value I was looking for. At this point I took a Alk measurement had got a reading of 10.4dkh. I did a second test to make sure the first wasnt a fluke and got a reading of 10.3dkh. The salt is rated to have a alk of 8.0 so I knew something was wrong.
I either mixed the proportions wrong (this is a 4 part salt mix similar to ESV), or my testing equipment wasn't working properly. I had a refractometer but I didn't have any calibration fluid at that moment so I didn't want to get a false positive or negative if the calibration was off. I then went up to my main tank and took a reading and got a salinity of 35.2, and a dkh of 6.8 using TM Pro Reef salt which seems reasonable.
With this being the case I was still confused because the Alk values were close to matching what TM says they should be in that salinity range, but the Formul8 Reef was way off. With this being the case I wanted to verify that the calibrations were correct using @Randy Holmes-Farley calibration recipes (http://reefkeeping.com/issues/2004-06/rhf/index.htm). Luckily I have access to reagent grade chemicals (I am a chemist) so I made up calibration standards for both refractometers and conductivity testers using NaCl and KCl respectively.
Conductivity:
Target: 3.2435 wt% KCl solution (6.487g KCl in 193.513g DI Water)
Refractometer:
Target: 3.65 wt% NaCl solution (7.30g NaCl in 192.70g DI Water)
I guess my main takeaways are that the refractometer should be my go to method for checking salinity as that appears to be the most accurate to the calibration standards. I am not sure what to make of the Hanna salinity tester. It reads extremely accurately when comparing to the 35ppt calibration solution that comes with it, but the KCl calibration solution was reading low by 0.7-0.8ppt. Should I trust the 35ppt from the Hanna calibration solution or trust the 34.2 from the KCl test? Have I missed anything obvious here?
When I get home from work today I will cross test the Hanna salinity tester against the refractometer and see what I get. I will also formulate a single gallon of the Formul8 Reef salt as written in the instructions and see what I get from that. Any thoughts would be appreciated!
I either mixed the proportions wrong (this is a 4 part salt mix similar to ESV), or my testing equipment wasn't working properly. I had a refractometer but I didn't have any calibration fluid at that moment so I didn't want to get a false positive or negative if the calibration was off. I then went up to my main tank and took a reading and got a salinity of 35.2, and a dkh of 6.8 using TM Pro Reef salt which seems reasonable.
With this being the case I was still confused because the Alk values were close to matching what TM says they should be in that salinity range, but the Formul8 Reef was way off. With this being the case I wanted to verify that the calibrations were correct using @Randy Holmes-Farley calibration recipes (http://reefkeeping.com/issues/2004-06/rhf/index.htm). Luckily I have access to reagent grade chemicals (I am a chemist) so I made up calibration standards for both refractometers and conductivity testers using NaCl and KCl respectively.
Conductivity:
Target: 3.2435 wt% KCl solution (6.487g KCl in 193.513g DI Water)
Refractometer:
Target: 3.65 wt% NaCl solution (7.30g NaCl in 192.70g DI Water)
I guess my main takeaways are that the refractometer should be my go to method for checking salinity as that appears to be the most accurate to the calibration standards. I am not sure what to make of the Hanna salinity tester. It reads extremely accurately when comparing to the 35ppt calibration solution that comes with it, but the KCl calibration solution was reading low by 0.7-0.8ppt. Should I trust the 35ppt from the Hanna calibration solution or trust the 34.2 from the KCl test? Have I missed anything obvious here?
When I get home from work today I will cross test the Hanna salinity tester against the refractometer and see what I get. I will also formulate a single gallon of the Formul8 Reef salt as written in the instructions and see what I get from that. Any thoughts would be appreciated!
