Simon_M
Active Member
I bought the Hanna Salinity Tester which comes with at least four sachets of Calibration Solution.
Some things I found out (most of it will be pretty obvious):
a. it's best to calibrate the Tester with the solution and then retest it to confirm that it the value recorded afterwards is also 35.0 ppt - if it's not then recalibrate until it is reading correctly. The instructions say to clean the Tester after use but when calibrating and recalibrating it is best to wait until afterwards and when calibrated, clean the Tester. I use RO water to wash down the Test equipment and deionised water for washing down and diluting for some of the tests e.g. Calcium, so RO water for cleaning the Tester.
b. if you press the Cal button after the Tester is already calibrated then the previous calibration will be "lost". This requires the Tester is recalibrated and my unit defaults to about 39 ppt. At least you know the calibration is lost? To avoid this, the Hanna Support suggest turning the Tester OFF. However, this is exactly what you don't want to do. Press Cal and the ON/OFF button will remove the calibration! The solution is simply to press the Cal button again and it will display "Esc" - the calibration is retained. This is the same behaviour as the pH probe but isn't documented in the SG manual. I only accidentally pressed the Cal button once, but I didn't want to use another sachet and (a) allows calibration again, anyway, if washing off is left until afterwards.
c. the salinity will reduce as the unit acclimates to the temperature of the DT water. When the temperature is stable then the reading is final and the wait symbol disappears. The Tester doesn't need to be switched on immediately e.g., put the probe end into the water and wait 20-30 seconds before turning it on will give the same reading and finish just as quickly.
d. I queried the calibration "document" for the Tester, because the uncalibrated Tester is 39 and not 35.0 in the Calibration Solution. The meaning of the calibration "document" is that the probe CAN be calibrated and used within the specified tolerances - once calibrated e.g., it's not calibrated and adjusted (trimmed) at the factory.
e. i have no idea if the calibration won't be reset if the Cal button is accidentally pressed and the unit allowed to power down without pressing the ON/OFF button. Or that the calibration won't be reset if the battery is changed. Something to try when I next calibrate the unit?
f. many users have reported that the calibration doesn't deviate over quite long intervals, so the need to recalibrate every month may be too cautious.
g. I'm not one to chase numbers, but the Tester is remarkably repeatable so the same reading is repeated at intervals (all things being equal). I do a 10% water change weekly and adjusting the DT salinity can be done in small increments if new water is mixed weaker or stronger knowing that the dilution 10:1 causes only about a 10% adjustment. I aim to increase/decrease the overall salinity by at most 0.2 ppt after a water change. Other attempts I have had to alter the salinity of DT water e.g., mixing extra salt in a jug of DT water haven't been quite so successful (with precipitation). Although it is often recommended to slowly increase salinity by adding salt to ATO water, I want the DT salinity to be "about right" before I do other tests since they are dependent on the salinity being "correct" or for an allowance to be made.
h. overall, I think it is a worthwhile "investment" for the DT because maintaining and adjusting salinity is one of the easiest things to "get right" and all other tests depend upon it. Fish and invertebrates seem to like stability too...
Some things I found out (most of it will be pretty obvious):
a. it's best to calibrate the Tester with the solution and then retest it to confirm that it the value recorded afterwards is also 35.0 ppt - if it's not then recalibrate until it is reading correctly. The instructions say to clean the Tester after use but when calibrating and recalibrating it is best to wait until afterwards and when calibrated, clean the Tester. I use RO water to wash down the Test equipment and deionised water for washing down and diluting for some of the tests e.g. Calcium, so RO water for cleaning the Tester.
b. if you press the Cal button after the Tester is already calibrated then the previous calibration will be "lost". This requires the Tester is recalibrated and my unit defaults to about 39 ppt. At least you know the calibration is lost? To avoid this, the Hanna Support suggest turning the Tester OFF. However, this is exactly what you don't want to do. Press Cal and the ON/OFF button will remove the calibration! The solution is simply to press the Cal button again and it will display "Esc" - the calibration is retained. This is the same behaviour as the pH probe but isn't documented in the SG manual. I only accidentally pressed the Cal button once, but I didn't want to use another sachet and (a) allows calibration again, anyway, if washing off is left until afterwards.
c. the salinity will reduce as the unit acclimates to the temperature of the DT water. When the temperature is stable then the reading is final and the wait symbol disappears. The Tester doesn't need to be switched on immediately e.g., put the probe end into the water and wait 20-30 seconds before turning it on will give the same reading and finish just as quickly.
d. I queried the calibration "document" for the Tester, because the uncalibrated Tester is 39 and not 35.0 in the Calibration Solution. The meaning of the calibration "document" is that the probe CAN be calibrated and used within the specified tolerances - once calibrated e.g., it's not calibrated and adjusted (trimmed) at the factory.
e. i have no idea if the calibration won't be reset if the Cal button is accidentally pressed and the unit allowed to power down without pressing the ON/OFF button. Or that the calibration won't be reset if the battery is changed. Something to try when I next calibrate the unit?
f. many users have reported that the calibration doesn't deviate over quite long intervals, so the need to recalibrate every month may be too cautious.
g. I'm not one to chase numbers, but the Tester is remarkably repeatable so the same reading is repeated at intervals (all things being equal). I do a 10% water change weekly and adjusting the DT salinity can be done in small increments if new water is mixed weaker or stronger knowing that the dilution 10:1 causes only about a 10% adjustment. I aim to increase/decrease the overall salinity by at most 0.2 ppt after a water change. Other attempts I have had to alter the salinity of DT water e.g., mixing extra salt in a jug of DT water haven't been quite so successful (with precipitation). Although it is often recommended to slowly increase salinity by adding salt to ATO water, I want the DT salinity to be "about right" before I do other tests since they are dependent on the salinity being "correct" or for an allowance to be made.
h. overall, I think it is a worthwhile "investment" for the DT because maintaining and adjusting salinity is one of the easiest things to "get right" and all other tests depend upon it. Fish and invertebrates seem to like stability too...
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