Need Salinity help!

[dtaranath]

For the past 3-5 years, I have used a refractometer to maintain the salinity in my tank. The tank was generally healthy; soft and LPS corals did pretty good, but SPS never really did well. Most wouldn't grow very well, despite good lighting, water flow, and other chemistry parameters. I kept the tank at about 35ppt (as calibrated with a 35ppt standardizing solution). My topoff was inconsistent, with the water sometimes reaching 30ppt (1.022), and I noticed all the corals starting to recede

Recently, in an effort to try and watch and maintain a consistent salinity with my topoff, I started using a PM2 module for my apex. I bought a new calibrating solution to calibrate the probe.

After I calibration, to my surprise, my tank water registered at around 26ppt (1.019)!! Which means that what i thought was low before, was EVEN lower!


Here's where i need help:

My tank is currently at 32ppt (1.024) as registered by my Apex PM2 salinity module. I have recalibrated my refractometer with the same solution that I calibrated the PM2. My refractometer is now reading about 43ppt (1.031). Yet, most of my SPS frags are finally growing, with the exception of some, which have died, but that may be due to placement in the tank. I'm nervous to take the PM2 to 35ppt, mainly because of what my refractometer is saying. Could it be that my refractometer has been wrong all this time? I'm assuming my refractometer is wrong, because surely SPS will not do well at 43ppt, correct?

I have no idea how to check which is right. Is the next step to check pure RO/DI water?

 

[downbeach]

The solution you're using for the Apex is a conductivity solution, and not made to measure refractive index for the refractometer. I would get a new 35ppt calibration solution for the refractometer. It would also be prudent to get a second opinion with another device(a different refractometer), in case the refractometer isn't working properly.

 

[Happyschneider]

You could also check with rodi for an immediate idea. If it does not read zero you know something is bad with the refractometer. However, if it reads zero, you still need to get a proper 35 ppt calibration solution.

 

[dtaranath]

The solution you're using for the Apex is a conductivity solution, and not made to measure refractive index for the refractometer. I would get a new 35ppt calibration solution for the refractometer. It would also be prudent to get a second opinion with another device(a different refractometer), in case the refractometer isn't working properly.

THANK YOU. That is actually quite reassuring. I will recalibrate my refractometer with the 53.0 mS calibrating solution from Pinpoint and reconfirm numbers. I had no idea the solution from Apex could not be used on refractometers.

You could also check with rodi for an immediate idea. If it does not read zero you know something is bad with the refractometer. However, if it reads zero, you still need to get a proper 35 ppt calibration solution.

Thank you also!! Very much appreciated. That will be also done!