Conflicting results with salinity

[Brandonmw]

I have always just calibrated my refractometer using ro water and have it dialed into 0 and my salinity is .026 right where it should be for a reef tank. I have recently just re calibrated my refractometer using calibration fluid. And when I test my water it is at .021. I purchase my salt water from a local store and they always have there mix at .026 I check with there meter every time and mine before I to water changes but my question is I am now very unsure which reading is correct as everything in my tank look good and healthy but now my salinity is way low according to the calibration fluid . Should I be looking at making changes or just go back to my ro calibrating as everything looks good and happy? 

[j.falk]

If your livestock looks good the way you have been doing things, I would not change your methods.  When you start getting into conflicting methods...who's to know which one has the correct reading?  There are so many variables when testing salinity.  This is why I pick one method of doing things and stick with it.  The livestock will tell you if there are problems just by looking at them and knowing what is normal and what is not.  If your livestock starts looking poorly...then try to figure out what you are doing wrong.  If the livestock looks good and you aren't seeing any problems...don't create a problem by changing things.

[GetPsyched2124]

Calibrating with RO water usually isn't the best though. 1.021 is on the low end, but if everything is  doing fine to your liking then there's no point in changing things.

A lot of LFSs keep their salinity around 1.021, mainly just the systems containing only fish.

 

[I'm Batman]

@GetPsyched2124 I asked my LFS what their salinity is and they said on the coral side 1.029 using brightwell and on the fish side it’s 1.026 using instant ocean. 
 

The other 2 reef shops keep theirs at 1.026 as well. Maybe that’s based by location? Not sure why they would keep it so low?

@Brandonmw

If the stores water tests at 1.026 and your RO calibration is 1.026, but the calibration solution gives you a 1.021, I’d go to the LFS with your refractometer a day test again. If it’s still 1.021 then it’d be safe to say you got some bad Calibration solution. 

[j.falk]

From what I've read, the lower salinity 1.021 is supposed to make it harder for parasites to thrive as well as provide a less stressful environment for fish.  

 

But it's for fish only tanks as GetPsyched2124 noted above.

[jservedio]

16 hours ago, I'm Batman said:

If the stores water tests at 1.026 and your RO calibration is 1.026, but the calibration solution gives you a 1.021, I’d go to the LFS with your refractometer a day test again. If it’s still 1.021 then it’d be safe to say you got some bad Calibration solution. 

If you bought calibration fluid from a legit company like Hanna, the likelihood of the calibration solution being off is pretty much impossible. Those solutions are used for lab-grade equipment and each batch is numbered and verified on equipment infinitely better than our hobby-grade stuff. You could even call/email them with a lot number from your bottle and get verification.

 

What is more likely is that the LFS's display tanks run at 1.026 to make it less stressful for the corals to be transferred, but the ASW they sell in bulk is 1.021. Or the refracto is poorly calibrated.

 

@Brandonmw, when you calibrate, make sure that your calibration solution is at the exact same temperature as your tank water. I just float my calibration fluid bottle in my tank for a few minutes. The refractive index of water changes with temperature (so does conductivity if you use a probe) - so they need to be the same temperature or close. I calibrate my refractometer with 35ppt fluid, but instead of matching that up to the 1.026 line on the refracto, I match it up to the 1.025 line since it is a much larger line and easier to see.

 

The build quality of hobby refractometers isn't that great, so if you are calibrating with 0ppt water, the scale likely isn't very accurate and when you get up to 35ppt, it'll probably be reading pretty far off. If you calibrate with 35ppt, it dosn't matter if the scale is off, since you are just aiming for that line.