thoughts and questions on calibrating refractometers, etc

[reefmaster70]

Ok. I was thinking about some things today as I was checking the calibration on my refractometers, and my Pinpoint digital salinity meter. I check them against a test solution ever few months just to be sure they are still "ON" and accurate.

Anyway, today I got to thinking, as I was reading some folks posts that they check their refractometers with fresh RO/DI water, and "Zero" out their refractometers using that method. I thought to myself, Huh, maybe I'll try that..I mean Zero is Zero (or in this case 1.000) right? How hard can that be.

HERE is where my questions about it come into play. How many do that, and have soft water? If your house has a water softener, then there is already some salt in your water and it would NEVER read 0 or 1.000 right? Or would the RO/DI unit take the salt out as well? I don't know. So I thought I'd test it. First, I used my usual 1.026 testing standard, and checked my two refractometers and my Pinpoint pH digital conductivity meter, and all of them were on at 1.026. So then I took some of my fresly made Ro/DI water from my storage tank (which is reading 0 TDS) and low and behold I had a reading of 1.010 on my refractometer. So.....if you are running a water softener is it safe to safe that you should NOT calibrate your refractometer to 0 or 1.000 sg? I guess I never thought about this today and am wondering how many people are zeroing out their refractometers that also have water softeners in their homes. This would throw your actual saltwater mixing off, by quite a bit if you do it that way.

Thoughts?

 

[Reef.]

Not a good idea to test with rodi water, best to test with salt water at the range you are testing for…a bad analogy coming up…you wouldn’t test a car can drive at 70mph by checking the meter reads zero when not moving.

Do yourself a favour and buy a Tropic Marin hydrometer, works every time and doesn’t need calibration, you can use it to keep your other testing methods in check if you prefer to use those.

 

[Privateye]

If you have 0 TDS then the sodium added from your water softener is not making it through the RO/DI unit. Sodium would be a dissolved solid. That being said, we measure salinity in terms of parts per thousand (or specific gravity) and water softeners typically treat in the parts per million range. So I wouldn't expect it to add a full ppt of sodium.

One thing that comes to mind about refractometers is they are calibrated for certain salinities and salts. I have two refractometers: one for seawater and one for brewing. The one for brewing was a lot cheaper, but the slope is slightly off from seawater. That means if I calibrate both of them at 0 ppt, the brewing refractometer will read off by about 2 ppt at full-strength seawater.

 

[reefmaster70]

Not a good idea to test with rodi water, best to test with salt water at the range you are testing for…a bad analogy coming up…you wouldn’t test a car can drive at 70mph by checking the meter reads zero when not moving.

Do yourself a favour and buy a Tropic Marin hydrometer, works every time and doesn’t need calibration, you can use it to keep your other testing methods in check if you prefer to use those.

I have a glass "float" hydrometer that I use occasionally, and I know they are the best for accuracy. I do test my refractometers against that as well. However, that still wouldn't tell me why I'd be reading 1.010 on my RO/DI water, when all of them are calibrated and read 1.026 across the board for my saltwater.

 

[NanoSteam]

I have a glass "float" hydrometer that I use occasionally, and I know they are the best for accuracy. I do test my refractometers against that as well. However, that still wouldn't tell me why I'd be reading 1.010 on my RO/DI water, when all of them are calibrated and read 1.026 across the board for my saltwater.

It's because the brine refractometers are only accurate within a certain range of where they are calibrated to. You'll never get an accurate ready with RODI with one unless you're using a seawater refractometer designed to be calibrated with RODI water which are much more pricey.

 

[reefmaster70]

It's because the brine refractometers are only accurate within a certain range of where they are calibrated to. You'll never get an accurate ready with RODI with one unless you're using a seawater refractometer designed to be calibrated with RODI water which are much more pricey.

that's kind of what I figured, but just wasn't sure, and never actually tested the theory. I've always calibrated at 1.026 and never looked back, but when I saw several people saying they calibrate with RO/DI water I thought I'd see what my refractometers would read after I calibrated them to 1.026. I figured they'd read 1.000.....I was wrong. :)

 

[Kooma]

I used to calibrate to RODI and once I realized my mistake I started making my own calibration solution. Rodi water with table salt and an accurate scale is all you need to bring yourself within an acceptable accuracy. I make about half a cup of it at a time and calibrate when I notice a change in my salinity of the tanks. With the ATO and tank size, even a half ppt takes months to drift down or up.

 

[exnisstech]

I never used rodi to calibrate and I don't remember reading any instructions that came with my refractometers stating to do that so I'm not sure how using rodi came to be recommended unless it's another Internet myth.
I used to use calibration fluid I bought then switched to Randy's diy fluid. Now I mix a batch of water once a week. I mix to 1.025 because that's where my tanks run. I verify the salinity with a TM hydrometer then I use that same water to calibrate my refractometers. Since I'm mixing once a week my refractometers are calibrated every week and it only takes a minute to check them.

 

[Gumbies R Us]

I use Calibration solution on my refractometer to make sure it is reading everything correctly

 

[BryanM]

I stopped trying and bought a TM Hydrometer.