Unexpected problem with refractometers... lol

Rick.45cal · Mar 15, 2017

I saw that post, it made me thankful I don't have a wife/kids and use an electronic refractometer

GoFish · Mar 15, 2017

GoVols said:
Anybody Following...
Trust me... Don't zero out your meter to RO water. Use 35 solution, it does makes a different.

Hmmm when I use RO to calibrate mine its right on target with my homemade 35ppt solution... why would you not zero your meter with RO for an instrument that sugggests doing so when it effectively coincides
We can't always trust store bought solution based on my experience. I've seen both Sybon and Pinpoint out of whack

Gator1970 · Mar 15, 2017

GoFish said:
Hmmm when I use RO to calibrate mine its right on target with my homemade 35ppt solution... why would you not zero your meter with RO for an instrument that sugggests doing so when it effectively coincides
We can't always trust store bought solution based on my experience. I've seen both Sybon and Pinpoint out of whack

You should use calibration solutions that bracket your target value - this way any instrument error should be accounted for. If you calibrate to one extreme or the other, any error in the instrument will be magnified more the further away your measurement is from from the calibration point. This is why ph meters use two solutions on either side of 8.3 for calibration.

GoVols · Mar 15, 2017

Gator1970 said:
You should use calibration solutions that bracket your target value - this way any instrument error should be accounted for. If you calibrate to one extreme or the other, any error in the instrument will be magnified more the further away your measurement is from from the calibration point. This is why ph meters use two solutions on either side of 8.3 for calibration.

Exactly!

I ran out of the solution and got lazy. Started zeroing out my meter to RO water. Thought my display was at 1.025. Got some more 35 solution and re-calibrated 3 months later. Well, After calibrating to the 35 solution my display was really at 1.021 sg not 1.025.

Note: Using two little fishes 35 solution, that is 35 natural seawater solution... not that it could be off too.

But you want to calibrate very close to your target as Gator1970 stated above

.

Hmmm... A Gator and a Vol agree

AllSignsPointToFish · Mar 15, 2017

I made my own homemade solution using Randy's recipe and my milligram scale. Solution should be 1.0264, and my Milwaukee refractometer read 1.026

Close enough for government work!

Rick.45cal · Mar 16, 2017

AllSignsPointToFish said:
I made my own homemade solution using Randy's recipe and my milligram scale. Solution should be 1.0264, and my Milwaukee refractometer read 1.026 Close enough for government work!

Looks good from my house!

Paul B · Mar 16, 2017

GoVols said:
Lol

That was a mangrove Island off Key Largo but I have taken it to Bora Bora and most of the Caribbean. I just make my water in between all those places and the fish get over it. There were a lot of manatees there that I was thinking of taking as a clean up crew, but the price of the plastic bag was too much and the airline frowns on taking manatees as they don't fit under the seat. Then there is the problem of them dislodging small frags.
I am also not sure how sensitive manatees are to differences in salinity.

GoVols · Mar 16, 2017

Paul B said:
That was a mangrove Island off Key Largo but I have taken it to Bora Bora and most of the Caribbean. I just make my water in between all those places and the fish get over it. There were a lot of manatees there that I was thinking of taking as a clean up crew, but the price of the plastic bag was too much and the airline frowns on taking manatees as they don't fit under the seat. Then there is the problem of them dislodging small frags.
I am also not sure how sensitive manatees are to differences in salinity.

Lol!!!!!!!!!!!

Thanks for making my day

Randy Holmes-Farley · Mar 16, 2017

GoFish said:
Hmmm when I use RO to calibrate mine its right on target with my homemade 35ppt solution... why would you not zero your meter with RO for an instrument that sugggests doing so when it effectively coincides
We can't always trust store bought solution based on my experience. I've seen both Sybon and Pinpoint out of whack

You may be asking that rhetorically, but there are clear reasons to use a good standard and not RO/DI. How do you know the standards were off? They might have been, but how do you know? In any case, you can make your own and be sure if you have a good scale.

Here is my standard explanation of why a 35 ppt standard can be a better choice:

No matter what manufacturers claim, there are reasons to use a standard other than RO/DI.

A perfectly designed and perfectly manufactured true seawater refractometer can be correctly calibrated with Ro/DI. If you totally trust them, go for it.

Even an imperfectly designed (e.g., brine refractometers, which make up the bulk of those sold to hobbyists) or imperfectly manufactured refractometer can be correctly calibrated to read 35 ppt seawater using a 35 ppt seawater standard. If you have any question about its accuracy, a good standard will eliminate the concern.

So it all boils down to who you trust.

Randy Holmes-Farley · Mar 16, 2017

Gator1970 said:
You should use calibration solutions that bracket your target value - this way any instrument error should be accounted for. If you calibrate to one extreme or the other, any error in the instrument will be magnified more the further away your measurement is from from the calibration point. This is why ph meters use two solutions on either side of 8.3 for calibration.

Well said.

Randy Holmes-Farley · Mar 16, 2017

GoFish said:
Hmmm when I use RO to calibrate mine its right on target with my homemade 35ppt solution... why would you not zero your meter with RO for an instrument that sugggests doing so when it effectively coincides

Then you either have a perfectly made true seawater refractometer, or an improperly made brine refractometer. lol

Myka · Mar 16, 2017

[QUOTE="GoVols, post: 3611162, member: 76040"]Note: Using two little fishes 35 solution, that is 35 natural seawater solution... not that it could be off too.

[/QUOTE]

The TLF solution, when compared to two Pinpoint solutions (one 2 years old, one just cracked open) is 2 ppt off! I can't remember which one is higher, but 2 ppt difference!!! what the heck!

Salinity measurement and refractometer calibration drive me freaking nuts. The solutions read different. Doesn't matter which ones you buy. It's a frickin joke. So frustrating! It's just salinity people (aimed at manufacturers), why can't you guys agree on this?!?!?!

I'm going to order some calibration weights for my digital scales. Hopefully I can make a solution that is more accurate, but I don't have faith in this...

@Randy Holmes-Farley is a $23 weight calibration set (Class M2??) anywhere near accurate? M2 kit: https://www.amazon.ca/American-Weigh-Scales-Calibration-Weight/dp/B003STEJAC

I see this Class F1 set for $150, that's doable. If you think it's worth it, I'll buy this one instead. I'm tired of this salinity battle. The weights are small though 1mg-5g. The heavier weight sets are over $1000. https://www.amazon.ca/Ohaus-Stainless-Steel-Calibration-Weight/dp/B0051WFBLK

EDIT: I found this weight class tolerances chart just now - looks like the M2 is a piece of crap (or at least the tolerances are huge... 10-20%!!!). http://www.troemner.com/media/downloadablepdfs/tolerance/weight_tolerances.pdf

GoVols · Mar 16, 2017

Well, After re-calibrating to my TLF solution.
I mixed up 15 gallons (for a water change) to 1.025sg and stored a lot in small bottles. (Got tired of paying $10 for a tiny calibration bottle)
Now I calibrate to 1.025 from my stored bottles. So, If my TLF solution is wrong then (lol) my sg is going to be off for along time.

DLHDesign · Mar 16, 2017

Paul B said:
I am also not sure how sensitive manatees are to differences in salinity.

Interestingly; not very. But they are mammals, thus they actually need fresh water to drink.

wattson · Mar 16, 2017

is there any info how to make the calibration fluid for refractos

Paul B · Mar 16, 2017

DLHDesign said:
Interestingly; not very. But they are mammals, thus they actually need fresh water to drink.

OK I give up. Where do they get that in the ocean? I have followed them and swam with them for a few days and never saw them coming out of the water for a drink, but I think, at night they crawl over to a swimming pool so they can get a drink of fresh water and maybe take a bath.

Or maybe they get it from the same place dolphins,whales and seals get it. Poland Spring.

LOL

GoFish · Mar 16, 2017

Randy Holmes-Farley said:
You may be asking that rhetorically, but there are clear reasons to use a good standard and not RO/DI. How do you know the standards were off? They might have been, but how do you know? In any case, you can make your own and be sure if you have a good scale.
......
No matter what manufacturers claim, there are reasons to use a standard other than RO/DI.
.......
A perfectly designed and perfectly manufactured true seawater refractometer can be correctly calibrated with Ro/DI. If you totally trust them, go for it.
.....
If you have any question about its accuracy, a good standard will eliminate the concern.

Sorry didn't mean for that to come off as a rhetorical. It totally makes sense to calibrate with a solution near target levels leaving less room for error. But just like saying these common brine water refractometers are better off being calibrated with 35ppt solution it should be known that these store bought solutions may be equally or more inaccurate than using RO @ 0.000
My buddy had his tank water checked and double checked by the local trustworthy fish store, that also verified his Sybon bottle was off. I believe they confirmed his tank water was @ 1.026 so it's a good thing he didn't make any drastic changes to his tank which would've been .0025 low...
The difference between our store bought solutions was 0.035. Are there any brands that are known to be 100% accurate for seawater solutions? And I should think about selling the Marine Depot brine refractometer and buy a seawater refractometer instead?

Myka said:
Salinity measurement and refractometer calibration drive me freaking nuts. The solutions read different. Doesn't matter which ones you buy. It's a frickin joke.

Touché. Totallly frustrating when you think you're buying the proper equipment and fluid to do things right. If you find a reasonably priced set of weights let me know. Never thought of checking the calibration of my digital scale but sounds like a good idea

GoFish · Mar 16, 2017

wattson said:
is there any info how to make the calibration fluid for refractos

This is from the article Randy wrote in 2004, posted on the previous page... and how I made my homemade solution...

"This 3.65 weight percent sodium chloride solution can be made by dissolving 3.65 grams of sodium chloride in 96.35 grams (mL) of purified freshwater.

For a rougher measurement in the absence of an accurate water volume or weight measurement:

1. Measure ¼ cup of Morton's Iodized Salt (about 73.1 g)
2. Add 1 teaspoon of salt (making about 79.3 g total salt)
3. Measure the full volume of a plastic 2-L Coke or Diet Coke bottle filled with purified freshwater (about 2104.4 g)
4. Dissolve the total salt (79.3 g) in the total water volume (2104 g) to make an approximately 3.65 weight percent solution of NaCl. The volume of this solution will be slightly larger than the Coke bottle, so dissolve it in another container.

[[Notice added post-publication: the standards described here that use Coke bottles are subject to variation in the volume of a 2-L Coke bottle. It has recently come to my attention that such 2-L bottles can vary in total volume, and that this can lead to at least a 1 ppt error in the salinity of the standards matched to seawater salinity of 35 ppt. Standards made with accurate measurements of salt and water should still accurately match 35 ppt.]]"

leptang · Mar 16, 2017

p7willm said:
A refractometer is measuring the difference in the speed of light in the air and in the liquid. They do not directly measure the specific gravity of the liquid or the number of particles in the liquid. They take that speed difference and tell you how dense or how much of a specific item dissolved in another item would cause the difference. If you dissolve an equal amount of salt, sodium chloride, and the stuff in sea water, sodium chloride and a lot of other stuff, in water the speed of light will change differently. The difference between a salinity and a salt water refractometer is how they interpret the change in speed.

They also make refractometers that are designed to tell how much sugar is dissolved in water that are used to test grapes.

This is why I fell keeping up on water changes is important... How many impurities change your hydrometers and refractometers... Maybe extra protein in the tank could throw off a true measuring of salinity?

Sabellafella · Mar 16, 2017

GoVols said:
Well, After re-calibrating to my TLF solution.
I mixed up 15 gallons (for a water change) to 1.025sg and stored a lot in small bottles. (Got tired of paying $10 for a tiny calibration bottle)
Now I calibrate to 1.025 from my stored bottles. So, If my TLF solution is wrong then (lol) my sg is going to be off for along time.

Lol i use to tlf stuff as well if i dont have standards to cross check test kits. Imo worth the 7 bucks