How accurate are refractometers?,

[VR28man]

They're both conductivity meters, so they both can have some of the same problems. Air bubbles and equipment interference can cause unstable readings. I think this is more of an issue with the Neptune probe since it's in your tank 24/7. If you're using a conductivity meter to spot-test salinity, it's easier to work around these problems. In my display tank the reading jumps all over, so I just put some water in a cup, drop the probe in, and give it a minute to stabilize. Works great.

I don't have any of these issues with my saltwater mixing station and my QT tank. I can drop the probe right in and get stable readings directly from the tank. This is especially handy when adjusting salinity. When I'm making saltwater, I usually add more salt than I need to. Then, I just adjust the salinity down by adding freshwater. I drop the probe in and add a little fresh water. If the salinity's still too high, I pump in a bit more until it reads where I want. Same with QT when I get a new fish. I drop the probe in the bag, get a salinity reading, then move the probe to the tank. I add freshwater with real-time feedback until the tank matches the bag. Then the fish goes right in.

Many hobbyists seem to be concerned with conductivity meters needing time to temperature compensate or being affected by interference from pumps and other equipment. I've never really understood this. It takes 2 minutes at most for the probe to temp compensate and it's easy enough to scoop up some water in a cup if there's interference. I know that wasn't really your question. I just really think that a lot of hobbyists miss out on a great way to test salinity because of some characteristics of conductivity probes that don't really end up being a problem in the real world.

Thanks, this does answer a lot (including useful stuff I didn't ask but which were logical follow on questions).

A refractometer is a very useful tool, however, it is meant to be a museum piece, or used as strictly a backup.;Pompus Get a Hanna digital salinity/temp checker and never look back. You’ll be happy you did.

Ha, indeed! And it doesn't look that much more expensive than some refractometers. Again, I've been quite unhappy with both one sample of the BRS refractometer (never got it to work properly, i assume it was a sample problem) and the Red Sea refractometer (can give odd results, and more importantly its hard to see sometimes). I may get the Hanna in the future.

 

[Daniel92481]

Yea, highly recommended. It only needs calibration about every 3 months. Takes about 5 seconds to test. The time saved could be used to drink a beer, or 3.

 

[LOVEROCK]

How do you guys read on your refractometer ? I notice there’s a blue line , and sometimes it shows like a slight white gap

 

[Reef.]

How do you guys read on your refractometer ? I notice there’s a blue line , and sometimes it shows like a slight white gap

Good question, my blue line looks slightly blurry sometimes, not sure why, next time it does it I’ll try adding more water to see if that’s the issue.

 

[minus9]

Using sun light will minimize the blurry affect of the line. I usually point mine towards my neighbors house so they feel like I'm spying on them, makes for interesting conversation when you run into them on the street. Just kidding, but use a bright light and you'll eliminate the blurriness.

 

[Reef.]

Using sun light will minimize the blurry affect of the line. I usually point mine towards my neighbors house so they feel like I'm spying on them, makes for interesting conversation when you run into them on the street. Just kidding, but use a bright light and you'll eliminate the blurriness.

That made me laugh, that’s probably the reason I’m getting the blurry line, I go to the window to check the reading and someone is always looking right at me, I feel a little pervy so back off a little from the window...I need to man up ;Snaphappy

 

[blasterman]

This is why I still use my old plastic floating needle hydrometer. I check it against a reliable and calibrated refractometer once a year and dont have to worry about it.

 

[MartinWaite]

They are accurate as long as you have calibration solution and are calibrating them. If not, they can be wildly inaccurate.

Think this depends on several factors these being 1. How well you look after it it terms of care given to it one drop can knacker it.
2. I keep mine in the same room as I'm going to be using it.
3. If you have a seawater or a saline refractometer I know in the UK there is only 2 that are for seawater the Red Sea one and the D&D one of which I own read differently to the saline one which is really made for cooking and doesn't account for the elements we us in our marine tanks and the saline one will read 1.5ppt more due to this fault. If you got a seawater refractometer it will show a range of 20 to 40ppt and a saline refractometer will read from 0 to 100ppt.
You shouldn't use RO water to calibrate a refractometer instead purchase a 35ppt solution to check and calibrate it that way you are calibrating the refractometer at near enough the result we want our seawater to be.

 

[SMSREEF]

YES use calibration fluid. I was using my RODI to calibrate and i was running 31ppt in tank when I figured it out. May have been cause of tank crash.
ALSO VERY IMPORTANT and rarely mentioned. Make sure you put the same amount of liquid on it. Too much or too little will give a different reading. Therefore if you have calibration fluid. You can put a set amount on let’s say 0.1ml. Set it to 35ppt. Then check it each time You make new water.

Same thing with me.
I was using RODI but when I brought some water into my LFS my salinity was actually 39ppt. Know wonder I was having problems at the time...
Now I use 35 ppt calibration fluid.

 

[Miller535]

Think this depends on several factors these being 1. How well you look after it it terms of care given to it one drop can knacker it.
2. I keep mine in the same room as I'm going to be using it.
3. If you have a seawater or a saline refractometer I know in the UK there is only 2 that are for seawater the Red Sea one and the D&D one of which I own read differently to the saline one which is really made for cooking and doesn't account for the elements we us in our marine tanks and the saline one will read 1.5ppt more due to this fault. If you got a seawater refractometer it will show a range of 20 to 40ppt and a saline refractometer will read from 0 to 100ppt.
You shouldn't use RO water to calibrate a refractometer instead purchase a 35ppt solution to check and calibrate it that way you are calibrating the refractometer at near enough the result we want our seawater to be.

Well yes. But I would assume that someone would take care of their equipment (if not I don't see why they would be concerned with accuracy), and also assume that someone is using a seawater refractometer. And the directions of them clearly state that they are ATC, temperature compensated and to keep them at the temp of the water being tested. I would really hope that someone would read the directions before they use something and take care of it.

 

[Reef.]

Well yes. But I would assume that someone would take care of their equipment (if not I don't see why they would be concerned with accuracy), and also assume that someone is using a seawater refractometer. And the directions of them clearly state that they are ATC, temperature compensated and to keep them at the temp of the water being tested. I would really hope that someone would read the directions before they use something and take care of it.

as you say they are temperature compensated, so no need to keep them at the water temp.

 

[Miller535]

as you say they are temperature compensated, so no need to keep them at the water temp.

Not exactly at the temp, but the directions do say to keep it around the temp. At one point in time I thought that ATC would compensate fully so I was keeping it in my basement near my mixing station, and it does not. And reads a bit off. Not a lot, but more then I like.

 

[SunnyX]

When properly tuned, they are very accurate.

I finally dumped my refractometer and picked up a Tropic Marin Hydrometer. Much better! No more calibration and messing around with water droplets.

Perhaps it was just my luck, but two refractometers had to be calibrated at least once a week.

 

[Anchor]

Having been a lab rat and using the refractometer quite a bit.. here is how I do mine. In a floating container with tank water fill with tank water and float your cal fluid.. 35 ppt. set your refractoerter on top of tank.. this will closely equalize cal fluid and instrument to the water you are going to test.. Use cal fluid in your refractometer. Adjust if needed.

Keeping the lens clean is important.., clean with RO after each use.

Everything should be rinsed 3 times.. standard lab practice.

dont shake, you should invert or swirl.

Wait. going to far for this discussion.

Basically I have 5 different ways to read salinity.. All of them come out equal (+/- 0.1 Spec gravity) when compared. 3 sal meters, 2 refractometers. I have 3 ways to measure pH.. they all read the same (+/- .05 for digital) I have 8 ways to measure temp both digital and glass.. None read the same but occasionally half will read within a degree of each other. Hobby grade stuff is not accurate generally.. Not if you want to be anal about it anyway.

 

[Miller535]

Having been a lab rat and using the refractometer quite a bit.. here is how I do mine. In a floating container with tank water fill with tank water and float your cal fluid.. 35 ppt. set your refractoerter on top of tank.. this will closely equalize cal fluid and instrument to the water you are going to test.. Use cal fluid in your refractometer. Adjust if needed.

Keeping the lens clean is important.., clean with RO after each use.

Everything should be rinsed 3 times.. standard lab practice.

dont shake, you should invert or swirl.

Wait. going to far for this discussion.

Basically I have 5 different ways to read salinity.. All of them come out equal (+/- 0.1 Spec gravity) when compared. 3 sal meters, 2 refractometers. I have 3 ways to measure pH.. they all read the same (+/- .05 for digital) I have 8 ways to measure temp both digital and glass.. None read the same but occasionally half will read within a degree of each other. Hobby grade stuff is not accurate generally.. Not if you want to be anal about it anyway.

Don't shake the calibration fluid?

 

[Reef.]

Don't shake the calibration fluid?

I’m thinking same reason you don’t shake water tests, bubbles can throw of the results.

 

[Miller535]

I’m thinking same reason you don’t shake water tests, bubbles can throw of the results.

If this is true then I have been doing it all wrong. I was always under the assumption that after sitting for a while the salt would separate from the fluid and need to be vigorously shook. No?

 

[Reef.]

If this is true then I have been doing it all wrong. I was always under the assumption that after sitting for a while the salt would separate from the fluid and need to be vigorously shook. No?

I don’t think shaking vigorously is needed, swirling should be enough, Salt I don’t think separates from the fluid that much I don’t think, I make my salt water for water changing for 2 weeks ahead, once it’s mixed I don’t mix it again for those two weeks, the salinity stays the same.

Saying that though, I can’t see shaking doing much harm.

 

[Miller535]

I don’t think shaking vigorously is needed, swirling should be enough, Salt I don’t think separates from the fluid that much I don’t think, I make my salt water for water changing for 2 weeks ahead, once it’s mixed I don’t mix it again for those two weeks, the salinity stays the same.

Saying that though, I can’t see shaking doing much harm.

I mix water ahead of time too. But I always turn the pump back on in the mixing station for at least a few min's before I use it. Not sure if it's needed, but surely doesn't hurt anything.

Particularly when the bottle of calibration solution is new, I wouldn't think swirling would move it much. At least with the BRS bottles.

 

[Reef.]

I mix water ahead of time too. But I always turn the pump back on in the mixing station for at least a few min's before I use it. Not sure if it's needed, but surely doesn't hurt anything.

Particularly when the bottle of calibration solution is new, I wouldn't think swirling would move it much. At least with the BRS bottles.

Swirling is quite effective...maybe next time you use the calibration fluid try one test before you shake, then one after shaking, see the results.

I do mix the quantity again I need for the water change when bring it to temp but when I've tested the standing salt water it was the same salinity.