Apex salinity question

[HeadOnAPlate561]

Quick question just set up my new (first) apex yesterday. Calibrated salinity when I set it up and was reading low. Even though refractometer was reading correct. Went to Lfs and theirs said low as well. Corrected my refractometer raised salinity. But my apex is still reading low. Any ideas?

 

[alyee5]

Did you calibrate the salinity probe? Are you using the temperature coefficient factor on the Apex? what is the difference in readings?

 

[Randy Holmes-Farley Verified Community Expert]

Be sure the temp is being measured in both the calibration fluid and in the test sample, and not in the tank.

 

[HeadOnAPlate561]

Yes I did calibrate it. I have always read salinity in sg and so far I haven't figured out if the apex will reado sp instead of ppt. But apex reading was about 30 ppt while refractometer was reading 1.022. then increased salinity to 1.025 according to refractometer and apex still shows just above 30. at 30.3. ideally it should be about 35. correct?

I increased salinity about 2:30. Is there a delay in reading.

 

[greg 45]

I would trust refractometer calibrated with a good solution. If you want to also check the probe test with this solution also. They aren't very reliable as I used one in a different controller. There must be good flow passing the sensor and they build up salt in the small opening in between the electrodes. I changed my tank by this reading and what a mistake that was.

 

[Randy Holmes-Farley Verified Community Expert]

30 ppt seawater has a specific gravity of about 1.0226
35 ppt seawater has a sg of about 1.0264

 

[alyee5]

+1....the salinity probe can be finicky...yes it should be reading in 35 ppt range at 1.025....yes, the reading should not be delayed.

I had to carefully follow the calibration procedure as demonstrated in the BRS video below...also after a water change my salinity probe it was drifting really low and had to shake it in tank water and re-plug it into the Apex module to snap it back into shape...

 

[HeadOnAPlate561]

Well thanks to the brs video that I probably should have watched earlier. shook the bubbles out of the probe and problem solved. duh. feel like an idiot now.

 

[alyee5]

Well thanks to the brs video that I probably should have watched earlier. shook the bubbles out of the probe and problem solved. duh. feel like an idiot now.

No worries...that's the great thing about this forum...quick, friendly honest advice and no judgments...
(besides I won't tell you how long it took me to figure out what was wrong with my salinity probe )

 

[Randy Holmes-Farley Verified Community Expert]

But the statement that 35 ppt is a sg of 1.025 is incorrect.