Salinity question
 

My conductivity probe reads 33.5 ppt and my refractometer reads 35 ppt or 1.026 SG. Neptune is telling me conductivity probe reads only nacl whereas refractometer reads total salts. So if this is true do I add salt to get my conductivity to 35 or leave it because my specific gravity is 1.026

Neptune is wrong. The conductivity meter reads, well, conductivity, which is influenced by all the charged particles in the water. The refractometer measures the refractive index, which is affected by the salts added. These articles have more:

http://reefkeeping.com/issues/2004-06/rhf/index.htm
http://reefkeeping.com/issues/2006-12/rhf/index.php#3

How have the conductivity probe and refractometer been calibrated?

I dial in my refractometer using RO water. The line between the blue and white is on zero. I calibrated my neptune conductivity probe using their 53000 siemen/cm solution. So my probe isn't calibrating correctly?

Its possible your refractometer isn't calibrated correctly. What kind of refractometer do you have?

I would read those articles bertoni posted. Very helpful and informative.

I'll also leave this here as well that may be of interest
Does your calibration solution need calibrated?
http://www.reefcentral.com/forums/sh...php?p=24570008

Even if you have a true seawater refractometer I would still use a 35ppt reference solution to check accuracy. But for the apex salinity probe you'll need a different solution then what I made in the link I posted. Randy also provided in one of his articles the recipe.

Refractometer says atc portable on it. Got it from brs. Ok. I'll give these a read. Thx.

Yes, please do. Your refractometer is not a true seawater refractometer. It's perfectly fine to use but you'll have to calibrate it near where you want the end point to be. Like a 35ppt calibration/reference solution.

I wouldn't trust an RO/DI calibration, even on a true seawater refractometer. That article should help. The PinPoint 53 mS conductivity calibration solution is fine for a refractometer, since it's made from artificial saltwater.

A note for the OP - it has been said that the Neptune solution does not have the correct refractive index to use for calibrating refractometers. I can confirm it's way off from 35 ppt when I checked mine.

So when bertoni recommends Pinpoint brand, it's because that manufacturer specifically claims that it will work for refractometers.


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I find calibrating @ 35ppt that RO shows as an ants whisker below 0

This is fine, for anyone wondering. You want your meter to be most accurate in the range you'll actually be using it. So anything above 37ppt or below 33ppt isn't critical to be spot on accurate. Although using DI water to calibrate to 0 could get you close at 35ppt, it's hard to have any confidence in your reading. I haven't even checked mine with DI water as it doesn't mean anything useful if you've calibrated at 35ppt