Hydrometer vs Refractometer

[Lanamonster]

Hi, All - I've been out of the hobby for 20 years. My tank has been up for about 5 weeks, and I've been monitoring SG by hydrometer, which has ranged from 1.022 to 1.024. However, the refractometer (Agriculture Solutions, Portable Refractometer) I just acquired is indicating an SG of 1.030. Any thoughts on this discrepancy would be welcome.

 

[PmCarbrey]

Have you calibrated the refractometer? They're not always accurate right out of the box. Having said that, your hydrometer may just be trash, they're notoriously inaccurate if they get any buildup on the swing arm

 

[Mastiffsrule]

I’m going with the hydro. After 30 years I just don’t trust those things. They need calibration and hard to see. I have a vertex refract and calibration solution in my closet. When I first got it I used it a lot. That stopped after the readings were the same.

The only thing to be super careful with on the hydro is if bubbles are on the arm it will raise the reading. Also they should be changed out after a while. Minerals can build up holding the arm down.

I’m going to be the only one though to say this. I’m a loner. Everyone else with say refrac, which isn’t a bad thing. Just me being old and stubborn

 

[Lanamonster]

Thanks for your response. My hydrometer is an old glass one from my homebrewing days; not sure how accurate it is either. As for calibration, I checked the refractometer against tapwater before using it, and it was reading right on 1.000. After my initial experiment, I checked it against a fresh bucket of salt water, and got 1.026. Having done that, I'm also aware that buckets and measuring cups aren't the most accurate things in the world, either. The two damsels in the tank continue to seem happy, so I think I'll leave things alone, buy a calibrating solution, and revisit.

 

[Mastiffsrule]

Can tell you’ve been in the hobby a while. I’m not sure how many would know about the glass one. I like them, the only thing on those is the water has to be 100% still.

It would be interesting to see if you have all 3 how they compare

 

[Lanamonster]

I'm curious, too, to see how they compare. And you're right; the glass hydrometer does bounce around a bit, even with the pumps off. I'll repost once I've dialed in the refractometer. Hopefully they'll be a little closer next time. Thanks, everyone!

 

[GThompson]

Can tell you’ve been in the hobby a while. I’m not sure how many would know about the glass one. I like them, the only thing on those is the water has to be 100% still.

It would be interesting to see if you have all 3 how they compare

I have all three and they are close enough together to trust anyone of them

 

[Sailingeric]

My beer refractometer is ok to calibrate with tap water but my SW refractometer I got from Bulk Reef Supply says to use calibration fluid and not water. I would get some and calibrate that way. Also I would get a scale to weigh out the salt and not just use a cup to measure salt.

 

[Lanamonster]

Hi, Everyone. Thanks for all the comments on this. There are some great articles on these forums regarding temperature and specific gravity. Upon inspection, my old homebrewing hydrometer is calibrated for 60 deg F, which isn't surprising given its intended application. Placing the hydrometer in a 78 deg bucket of tap water confirmed my suspicion that the readout was artificially low in my tank; applying a correction puts it pretty close to the SG from the refractometer. As for the refractometer, it was OK when I tested it using a reference solution. I'm due for a water change this weekend, so I'll work on getting the SG down when I do that. I'll also be using the refractometer from now on. For Sailingeric, thanks for the suggestion regarding a scale; I've been thinking about that, too, and I'll pick one up this weekend. Live and learn, right? Thanks again, everyone!

 

[Peace River]

Here is a link on a DIY solution to calibrate your refractometer. Good luck!

Given the choice between a hydrometer and a refractometer, I'd pick the Milwaukee digital refractometer!

 

[Peace River]

[...]
I’m going to be the only one though to say this. I’m a loner. Everyone else with say refrac, which isn’t a bad thing. Just me being old and stubborn

Although this may be true, you're still a fan favorite!!!

 

[Neil S.]

I've used a float hydrometer (glass type) since starting. If you get one that was calibrated for sea water testing, with a narrow range for the entire scale, you'll have a good level of accuracy. They use these to calibrate the digital refractometers.....so I figured I'd just use what the digital companies use to calibrate with. So far my water's SG is very stable at 1.0256 (yes the glass float hydrometers can get that accurate). Easy and fast to use.

 

[Ebslinger]

From personal experience, the paper piece in the hydrometer can move... and often does.

As for refractometer (which I use), it needs occasional calibration... Using RO/DI water to assure it's a 0, and a solution of 35ppm is a good way to ensure a proper calibration.

The RO/DI at 0 is often used as a second set point in my lab.

 

[Lanamonster]

One last question. I'm thinking it's probably better to bring salinity down slowly over several day. Any thoughts?

 

[Ebslinger]

If you have an ATO, just pull out small amounts of H20 over time... the ATO will fill with clean H2O.

No ATO, very, very small changes.

 

[Lanamonster]

No ATO, so small changes it is. Thanks, everyone!

 

[Neil S.]

From personal experience, the paper piece in the hydrometer can move... and often does.

As for refractometer (which I use), it needs occasional calibration... Using RO/DI water to assure it's a 0, and a solution of 35ppm is a good way to ensure a proper calibration.

The RO/DI at 0 is often used as a second set point in my lab.

You have a good point, generally this is a problem with the cheaper (think Marin or Fluval glass hydrometers). However the good ones don't have that as an issue. (but they also cost a fair bit more). I think so long as care is taken then the larger of the Marin hydrometers is okay, just don't shake it dry.

 

[Billdogg]

I have two swing arm and one floating (lab grade) hydrometers as well as a refractometer. Are the swing arm's dead on accurate? Nope. They are, however, very consistent, and once calibrated with my floater have been a mainstay of my systems for over 30 years. I just marked them where 1.026 really is and they've been just fine since. (FWIW - one of them read about .002 low, the other was about .003 high) The refractometer is also very accurate, but IMO, not as simple to use. I use whichever is handy, knowing that in the end, they are only as accurate as the person using them.

 

[Neil S.]

I have two swing arm and one floating (lab grade) hydrometers as well as a refractometer. Are the swing arm's dead on accurate? Nope. They are, however, very consistent, and once calibrated with my floater have been a mainstay of my systems for over 30 years. I just marked them where 1.026 really is and they've been just fine since. (FWIW - one of them read about .002 low, the other was about .003 high) The refractometer is also very accurate, but IMO, not as simple to use. I use whichever is handy, knowing that in the end, they are only as accurate as the person using them.

Awesome! I've always liked the accuracy and ease of use of the glass float hydrometers. My brother, in the early 80's was using one on his first saltwater aquarium. I acquired a lab grade one and haven't regretted not getting a refractometer. I check my salinity once a week during feeding time when the pumps are off. Just drop it in, wait a minute or so to let the temperature equalize....and read, so simple. I'm running a Triton Method tank (new) which means that I won't be doing too many water changes, but tracking the SG to make sure the ATO and the Triton Method don't alter it.

 

[HunterW]

I’m going with the hydro. After 30 years I just don’t trust those things. They need calibration and hard to see. I have a vertex refract and calibration solution in my closet. When I first got it I used it a lot. That stopped after the readings were the same.

The only thing to be super careful with on the hydro is if bubbles are on the arm it will raise the reading. Also they should be changed out after a while. Minerals can build up holding the arm down.

I’m going to be the only one though to say this. I’m a loner. Everyone else with say refrac, which isn’t a bad thing. Just me being old and stubborn

I have been researching refractometers big time. I have had hydro's since the 70's and ran a tank off of that for years BUT wadn't doing corals. Had great fish growth and spawning by clowns. I am on a budget but should I get a refractometer when I take one rank to a reef tank? Thanks.