Trust Refractometer or Hydrometer

TangerineSpeedo

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With the plastic Hydrometer, there are too many variables that can influence the reading (air bubbles, made by children in a foreign country, etc.) I have three different refractometers and they all read slightly different. But I do have one that once it is adjusted to 35ppt it will also read O with distilled water. Never the less it will read different from my Hanna and my Milwaukee. There are reasons for that, but I won't get into that because it will just confuse you more. The best is the aforementioned Tropic Marin Hydrometer, I would suggest you pick on up, you will not use it all the time but you will use it to reference your other methods. But using it, it MUST be at 25 dg C or 77 dg F to be accurate.
But we have to deal with what you have right now, and that is a refractometer and a home made solution. I would suggest you adjust your refractometer to your solution. Then prepare another solution and retest. If it is the same you are good to go. If you have to raise your salinity. I would add more saltwater to your tank the concentration it is now. and let the water evaporate which will raise your salinity slowly. If it is too high in salinity, take out some water and put in some fresh. But do not lower it more than a point a day to keep everyone happy.
Until you learn why instruments read different, it will be best you use your refractometer and be consistent about using it. Your LFS may be different that yours, but who says theirs is right.
 

MBruun

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A floating hydrometer, like the one from Tropic marin, is the most accurate salinity measurement tool.
It does not depend on calibration like a refractometer, but require the use of a calculator application like the links below to get the actual salinity.
Most refractometers use ATM (automatic temperature adjustment) and will give a very accurate result.

 

Thumbster

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So I made this solution by measuring everything and mixing it up and my refractometer is reading 1.016. Should I calibrate it to the 1.026 that it should be to match with the 35ppm? Also, this makes sense why the hydrometer is going above because if this is correct then the salt in my tank is running about 1.030. Not sure if anyone is up to respond to this.
If you made the solution correctly it should read 1.026/35ppt on your refractometer.

As a side note, this solution is ONLY for the refractometer. There’s a different solution if you’re using a hydrometer and yet another for a conductivity meter.

Here’s the article explaining how it works.
 

merkmerk73

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Just don't trust a hydrometer, I've made that mistake as a beginner. Refractometer has the most accurate measurements, I myself use a milwauke digital refractometer but handheld ones are just as accurate. Hydrometer often get stuck or jammed and just isn't a good tool

I don't think the TM hydrometer is a typical hydrometer that you think of when you think of one that gets stuck or jammed
 

Rusty_L_Shackleford

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Everyone swears by the tropic marin hydrometer which is a big giant thermometer looking thing.

It does seem to be extremely accurate.
This is exactly what i use. I got tired of constantly having to constantly calibrate the refractometer. Plus the little Guage was getting a little hard to read. The hydrometer is much easier. I have a digital refeactometer but never even use it. Might just sell it one of these days.
 

salty joe

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Refractometers are great for their convenience. Problem is, they get out of calibration. I use that that big honkin Tropic Marin hydrometer and adjust my refractometer accordingly.

If your tank is doing well, it might be worthwhile to hold off doing anything until you get a TP hydrometer. For ease of use, I made an acrylic tube I fill with water. Turning off the pumps and reading it from outside the tank is a hassle for me. Just like the swing arm type, you have to make sure the TP is free of air bubbles. The TP is going to be on the money.

BTW, where a refractometer really shines is acclimation when the fish come in with low salinity.
 

Dburr1014

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Thumbster git it right posting RHF's article.
Follow it to make your own solution for the refractometer.

Then, what I did, take the swing arm once you're system water is spot on where you want run, is to mark the swing arm with a magic marker. Now you have 2 forms to measure the salinity.
I got lucky with my 10 year old swing arm I think. It's always read spot on with my refractometer. I use it for quick checks when making a fresh batch of salt. When I get close to the sg, I switch over to the refractometer.
 

RichReef

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After having a serious issue with salinity crashing my entire system I will only use a refractometer calibrated with BRS calibration fluid or TLF fluid. On top of that I use 2 refractometers at a time all the time.

Have not had a single salinity issue since.
 

dschuffert

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I prefer a refractometer over a hydrometer. I like to use 1.025 calibration fluid to calibrate the refractometer. I also use an electronic Milwaukee salinity device (that needs calibration too).
 

XtraKargo

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I'll throw a vote in for the Tropic Marin Hydrometer as well. I keep it around to tune my refractometers to it, along with family and friends units. But you have to have the water at the correct temp, like mentioned before. Neat piece of kit, and really not too pricey for the accuracy it provides. (I use one of the 10 dollar pen style thermometers off amazon for meat to check temps quickly.)

Good luck!
 

Gavin Noy

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Hey, so I broke my old hydrometer and it was a very old hammy down hydrometer. So I decided to buy a refractometer to get better results. Now, I got it and I put RO water on it and it tested at the 1.000 that it says it should, and then I put my tank water on it and it tested at 1.020 which didn't seem right. So instead of dumping a bunch of salt I went to my local Petco and got a hydrometer and tried that it has a range of 1.014-1.028, and the hammer in it is going to the surface of the water reading higher than 1.028. So, which one do I trust? Is the hydrometer I bought compatible with saltwater? From what I read they are all the same. I'm gonna post links to both the hydrometer and refractometer.


I have the same refractomiter and out of the box it was bang on when tested with calibration fluid at 35 and RO water at zero.
 

Naekuh

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You can calibrate a refractometer with distilled water?
Am i the only one that feels dumb for not knowing this and always picking up the 35pt solution to calibrate it?

I also use a Hanna, but i like to double verify with a trusty refractometer.
 

Reefkeepers Archive

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You can calibrate a refractometer with distilled water?
Am i the only one that feels dumb for not knowing this and always picking up the 35pt solution to calibrate it?

I also use a Hanna, but i like to double verify with a trusty refractometer.
It's what I do anyway, works for me. Though @Randy Holmes-Farley probably would know more on that matter
 

Dburr1014

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You can calibrate a refractometer with distilled water?
Am i the only one that feels dumb for not knowing this and always picking up the 35pt solution to calibrate it?

I also use a Hanna, but i like to double verify with a trusty refractometer.
You are doing the right way of calibrating.
RHF has a whole article on the subject.

It's what I do anyway, works for me. Though @Randy Holmes-Farley probably would know more on that matter

Read this and why you should not use distilled water for calibrating.

 

Narideth

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I have an entire thread on trying to sort why my corals were unhappy and finding out that my salinity was somewhere around 1.017 because of all things, an unexpectedly poor result on a magnesium test and then the debacle of testing with multiple pet stores and multiple devices to try and figure out what was actually accurate once someone mentioned that my salt could be off.

This event included purchasing two different salinity fluids, and having attempted to calibrate my refractometer with bad results on both as well as distilled water. The purchased fluids were off and each one gave me different results. I ended up getting the big TM glass hydrometer and now I use it to calibrate my refractometer periodically. It removes a degree of human error and gives me a bit of peace of mind after that madness.
 

Randy Holmes-Farley

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I ended up getting the big TM glass hydrometer and now I use it to calibrate my refractometer periodically. It removes a degree of human error and gives me a bit of peace of mind after that madness.

Playing the devil's advocate, it removes some of your possible testing errors, but not the possible human error in manufacturing the hydrometer, or the possible error of the paper moving later.

IMO, it is worth checking at at least once.
 

TangerineSpeedo

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Playing the devil's advocate, it removes some of your possible testing errors, but not the possible human error in manufacturing the hydrometer, or the possible error of the paper moving later.

IMO, it is worth checking at at least once.
Checking against what…? lol.
You are right, human/manufacturing error is a factor. But what can one do to exclude any of that.
I love the statement people make and say I use this or that product and it is never off. But tested against what? The best hope you can have is for consistency at our level/price point.
At least I have the ocean next to me so that I have a testing reference.
 

Randy Holmes-Farley

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Checking against what…? lol.
You are right, human/manufacturing error is a factor. But what can one do to exclude any of that.
I love the statement people make and say I use this or that product and it is never off. But tested against what? The best hope you can have is for consistency at our level/price point.
At least I have the ocean next to me so that I have a testing reference.

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com

Specific Gravity Standard

Most aquarists recognize that inexpensive hydrometers are often prone to error. In some cases, inaccuracy is due to poor manufacturing, and in other cases it is due to poor usage by aquarists. In a previous article I tested several hydrometers and found variable results, from good to marginal. Beyond the inherent accuracy of the measurement is the confusing problem of how specific gravity relates to the temperature of the measurement, an issue which I detailed in that same article.

The best way to be sure that a given hydrometer is giving accurate information is to check its accuracy in a solution with a density (specific gravity) similar to the aquarium water. In order to provide a standard for hydrometers, a solution of a similar specific gravity to normal seawater is required. Seawater with S= 35 has a specific gravity of about 1.0264 (Tables 1 and 3).

In order to match this specific gravity to a standard solution made from sodium chloride, look up the density of different sodium chloride solutions in the scientific literature. My CRC Handbook of Chemistry and Physics (57th Edition, Page D-252)4 has such a table (partially reproduced in Table 4), but it has data only for 20ºC (68ºF). Specific gravity at 20ºC is then easily calculated by dividing the density of the solutions by the density of water at the same temperature. This table (4) can then be compared to seawater at 20ºC (Table 5). The primary purpose of showing specific gravity at 25ºC (77ºF; Tables 1 and 3) and 20ºC (Table 4) is to show that specific gravity does not change much with temperature (1.0264 vs. 1.0266). Nevertheless, it is only the 20ºC data that will be used to devise a standard.

The table in the CRC Handbook has entries for 3.7 and 3.8 weight percent solutions of sodium chloride that span the specific gravity value for normal seawater. Interpolating between these data points suggests that a solution of 3.714 weight percent sodium chloride has the same specific gravity (and density) as S=35 seawater, and can be used as an appropriate specific gravity standard (Table 5). For most purposes, 3.7 weight percent is accurate enough.

To produce a 3.714 weight percent sodium chloride solution, dissolve 6.20 grams (1 teaspoon) of Morton's Iodized Salt in 161 mL (161 g) of fresh water (making a total volume of about 163 mL after dissolution of the salt). This solution can be scaled up as desired.

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

1. Measure ¼ cup of Morton's Iodized Salt (about 73.1 g)
2. Add 1½ teaspoon of salt (making about 82.4 g total salt)
3. Measure the full volume of a plastic 2-L Coke or Diet Coke bottle filled with purified fresh water (about 2104.4 g)
4. Add an additional 2 tablespoons of purified fresh water (about 30 g)
5. Dissolve the total salt (82.4 g) in the total water volume (2134.4 g) to make an approximately 3.7 weight percent solution of NaCl. The volume of this solution is larger than the Coke bottle, so dissolve it in another container.
 

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