Refractometer/Hydrometer/GHL
 

I am having some serious measurement reading issues on my refractometer, hydrometer, GHL Profilux 3.

First I calibrated the refractometer with clean ro/di, freashwater (TDS 134) and set it at zero. I then calibrated my GHL probe with the factory 50mS fluid at 77 degrees. The refractometer now reads at 1.025 and the hydrometer and GHL probe are both reading at 1.0213.

I have done this over and over numerous times hoping for a different outcome but each time the same results.

I also have a pinpoint salinity probe at it as well (when calibrated with the factory 53.0mS) it too reads completely different than any of the other measurement tools.

Hoping to get some reef guru's to help me out here.

Thank you all in advance.

All the calibration fluids including the fresh water should the same temp as the tank. The profilux has a density offset that also needs to be set after calibration. If it's a good quality refractometer and calibrated properly I would use that as the guideline and set the profilux offset to match. You can try RO or distilled water with the refractometer but it shouldn't make a difference.

Thanks for the info. The refractometer is a Sybon salinity and I assume its not a bad quality one. I will use the refractometer as a guideline to set my GHL but it still puzzles me that the hydrometer and the Pinpoint are not within the same parameters.

GHL: 1.0213
Pinpoint: 53.0 (1.026)
Instant Ocean Hydrometer: 1.025
In-sump bobbing Hydrometer/Temp: 1.022

I just tried the calibration fluids that came with the GHL and the Pinpoint and this is what my refractometer measured.

GHL 50mS @ 25 degrees: 1.018

Pinpoint 53.0mS @ 25 degrees: 1.028

Makes no sense to me. Perhaps the calibration fluids are contaminated or old?

Contamination seems unlikely as both of the bottles have never been left open and are under 30 days old from both manufacturers (store purchased).

First of all, if the Sybon refractometer is a standard salinity refractometer then calibrating it with water will result in error at standard salt water aquaria salinity.
Even if you have one of the few sea water refractometers, it's still recommended to use calibration fluid to set it.
http://reefkeeping.com/issues/2006-12/rhf/index.php

Firstly, I wouldn't worry about the hydrometer reading as they cannot always be trusted ( put it in a drawer and forget about it )
As for calibrating the refractometer;
Mine requires me to have the solution @ 68f. I take a digital thermometer with me and wander around my basement until I find that room temperature. Then I put a drop on the lens and wait a couple minutes for it to equalize before I close the cover. I've never had an issue with it when I do this.

A TDS of 134 is really high for ro/di. It should be closer to zero. It could be throwing off the calibration.

I don't have the link on me as I am on my iPad, but shoot micheal a pm (aqua digital) he has a thread on rc about the reasons why and how to calibrate the ghl properly....

Steve

Makes sense to me, like I said the GHL offset needs to be set. Throw out the hydrometer reading and things make more sense. The refractometer reads 1.025 while the pin point reads 1.026. I would sway towards the refractometer being more accurate than the pin point but the fact these are very close is a good sign. So you can assume the refractometer is accurate so set the GHL offset to match.

Refractometers should be calibrated with a seawater calibration fluid.
Swing Arm Type Hydrometers are only good for hockey pucks
Pinpoint Meters... no comment but I gave up using them a long time ago.
Floating hydrometers I don't use either.

Make sure the GHL Cond probe is cleaned and swish it through the calibration solution to get rid of any air bubbles.

Cheers,
Tim