What salinity to trust?

Salty_Box_Reef · May 11, 2017

So I have a atc refractometer that I had been "calibrating" with RO/DI water. Found out thats not the best way to calibrate it and purchased some Aqua Craft 35ppt calibration solution. Based on that it turns out I was running my tank at around 30ppt/1.022. So I raised my salinty to 35ppt/1.026.

I also have a new apex with salinity probe. At 35ppt on the refractometer it was reading 42ppt. I purchased some neptunes 53.000 calibration solution and re calibrated it. The probe reads 35ppt in the solution after calibration, but 38.8 in my tank.

So now my refractometer reads 35ppt with tank water and 35ppt with AquaCraft solution, but the neptune conductivity solution makes it read 1.020.

So whats right? What else can I do to triple check everything?

My tank is experiencing some issues so i would like to rule out salinity asap.

Shaddow_wolf169 · May 11, 2017

You tank is really high I would agree with the probe. If it read high twice

terri_ann · May 11, 2017

You know that's a loaded question, right?! Various things can be done however, IMO, I would go with the Apex/Neptune's. If the probe and calibration solution is reading the same/correct, then I would say the salinity in the tank is off/high. I would then slowly lower it.

High Plains Reefer · May 12, 2017

do not go with the apex trust your refractometer my apex reads 45+ they go by electroconductivity so any number of things can cause the salinity to read high according to the apex

Salty_Box_Reef · May 12, 2017

So see my dilemma? I need a more definitive result.

Shaddow_wolf169 · May 12, 2017

Mix a perfect batch of salt test with the refract the then probe. Then take the water to the lfs and get a second opinion

120reefkeeper · May 12, 2017

I have a refractometer, Apex Salinity probe and a Milwaukee Digital Refractometer . The Milwaukee and the regular refractometer read the same. My apex probe has always been off a little.

reeftilldie · May 12, 2017

Ur refractometer with 35ppt calibration is ur best toy.

Pongo · May 12, 2017

If your refractometer is calibrated with 35ppt solution and your tank water then reads at 35ppt with the refractometer - use the tank water to calibrate the Apex probe.

After calibrating the Apex probe, you can adjust the temperature compensation to get it close to 35.
Then just use the probe to alert you if something changes drastically.

terri_ann · May 12, 2017

Ssteve, as you can see, there are many things that can be done and said, not to mention other variables when testing such as temperatures, tolerances allowed within a standard, etc. Again, IMO, I strive for the closest accuracy and "consistency". That's what's important to me for tanks. Good luck!

Water Dog · May 12, 2017

Use your calibrated refractometer for your specific salinity numbers. Use the Apex conductivity proble to recognize trends. The Apex is a pain to keep consistent. Mine always read higher even after proper calibration. Any air bubble build up on the tip of the probe and it will be off. If you don't have a dedicated temperature probe with your PM2 (Classic Apex), it will be off. Ended up getting rid of the PM2 as it would just give me something extra to fret about. I use a Milwaukee digital and cross reference it with a calibrated refractometer from BRS.

Shaddow_wolf169 · May 12, 2017

Has anyone ever check to see if there probe reads high due to a minute amount of electricity in the water?

Randy Holmes-Farley · May 12, 2017

Ssteve said:
So I have a atc refractometer that I had been "calibrating" with RO/DI water. Found out thats not the best way to calibrate it and purchased some Aqua Craft 35ppt calibration solution. Based on that it turns out I was running my tank at around 30ppt/1.022. So I raised my salinty to 35ppt/1.026.
.

The refractometer should not have read that far off when calibrating with RO/DI (the offset is a known specific amount), and it suggests either the refractometer is poorly designed (i.e., not working right), or the standard is not correct.

Randy Holmes-Farley · May 12, 2017

Try the conductivity probe in a cup of water outside the tank.

A good conductivity meter system will have no such interference, but some people report issues with the Apex.

Berlibee · May 12, 2017

Check this: https://www.reef2reef.com/threads/i-run-my-system-at-1-029.230701/ but read the full story

Salty_Box_Reef · May 13, 2017

So I recalibrate my prob with solution I floated in the tank. So about 78deg. The tank now reads 37ppt. If I calibrate my refractometer with fresh rodi then my refractometer reads 37ppt. However if I calibrate it with the calibration solution then it reads 39ppt.

At this point I'm beginning to think the solution is off and my salinity is high.

Randy Holmes-Farley · May 13, 2017

Calibrating a brine refractometer with Ro/DI will cause it to be off by 1.7 ppt and it will read too high.

When you used the calibration solution, do you set the device to 35 ppt or sg = 1.0264 (you cannot generally do both at the same time). unless it is a true seawater refractometer)