Refractometer and distilled water

[jc061471]

Can someone tell me exactly why distilled water isn't recommended to calibrate a refractometer?

[mako61]

You want the calibration value close to the desired measurement value to reduce error. Thats around 1.026 SP hence you want to calibrate to 1.026.

[Ron Reefman]

The further the readings you are looking to get 1.022 to 1.027 are away from the point you calibrate at 1.000, the bigger the error rate could be. But I've never tried calibrating a refractometer to 1.000 and then tested it against a calibration fluid to see how big the error rate is. I suspect it's quite small.

I calibrated my hydrometer to a see it's error rate and I found it to be -0.004. I put a label on it with the error rate so I wouldn't forget. That was 5 years ago and it has been tested about 12 times (quarterly at first and then semi-annually) since then and has always been off by the exact same amount. I quite testing it about 18 months ago. My refractometer is just collecting dust!

[Kadee]

The calibration instructions that I received with my refractometer (ATC) directed to use distilled water as the calibration fluid for adjustment to zero.

[FugeReefer]

Using distilled or ro/di water only calibrates your refractometer against have a false high reading. Your refractometer could still read a false low( i.e. it could read 1.025 and actually be higher.)

Using a control solution to calibrate your refractometer will set it to read a true measurement.

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[d0ughb0y]

salinity scale is linear, so calibration can be done at any point. calibration for 1.0 is just as good as at 1.026. If that is not the case, there is something wrong with the refractometer.

[Yogre]

This article by Randy Holmes-Farley discusses refractometers and their calibration.

It also discusses why the refractometers most of us use should not be calibrated with distilled water, but a 35ppt standard.

http://reefkeeping.com/issues/2006-12/rhf/index.php#14

[d0ughb0y]

the reason is because you may be using the wrong type of refractometer.

the science behind the linearity of salinity scale is sound. if it does not work, the issue is with the refractometer, as the linear scale may be offset. it is still and always will be linear.

a good way to measure is by hydrometer, as it is based exactly on definition of Archimedes' principle, which has stood the test of time. All other means of measurement (light refraction, electrical conductivity) are mere approximation.

[mcgyvr]

IMO if the instructions say to calibrate with RO then do so.. If they say to calibrate with a 35ppt standard then do so..

[Gladmaker]

I believe a hydrometer is accurate if used properly. There must be no air bubbles on the indicator. If there is, then pour the water out and try again. Also, it should be rinsed with the water to be tested before filling with the sample water. After use, it should be rinsed with clear water to remove salt residue.

[Yogre]

The difference is the fact that most of the refractometers sold for use in the hobby are salt refractometers, not true seawater refractometers. If you're using a salt refractometer to measure a brine solution, the you're fine to calibrate to zero using distilled water.

According to Randy's article, if you calibrate to zero with a salt refractometer, you will read a 35ppt seawater solution as 33.7ppt. It's not super far off, but it's off. That's why I calibrate my cheapo Sybon refractometer with a 35ppt standard.

The only true seawater refractometers I'm aware of are the Vital Sine and the VeeGee, as well as the Milwaukee digital instrument.

Read the article, which was written by a PhD chemist. Or, check on this subject in the Reef Chemistry forum.

[Ron Reefman]

Originally Posted by Gladmaker

I believe a hydrometer is accurate if used properly. There must be no air bubbles on the indicator. If there is, then pour the water out and try again. Also, it should be rinsed with the water to be tested before filling with the sample water. After use, it should be rinsed with clear water to remove salt residue.

Oh I don't thing so. Sorry.

I've talked a few friends into using their hydrometer after calibrating it. I've done 2 of my own and 3 for friends and they ranged from being 0.002 off to as much as 0.005 off. The big thing about hydrometers is, they are crazy reliable over time if you use them properly.

[Gladmaker]

Originally Posted by Ron Reefman

Oh I don't thing so. Sorry.

I've talked a few friends into using their hydrometer after calibrating it. I've done 2 of my own and 3 for friends and they ranged from being 0.002 off to as much as 0.005 off. The big thing about hydrometers is, they are crazy reliable over time if you use them properly.

I think that's basically what I said. 0.002 is accurate enough. I don't know how you could calibrate a hydrometer. You said they are crazy reliable over time if you use them properly. I believe that's what I said.

[ericarenee]

^^^ You do not really calibrate them. You just find how much they are off and adjust accordingly

[slief]

Originally Posted by Gladmaker

I think that's basically what I said. 0.002 is accurate enough. I don't know how you could calibrate a hydrometer. You said they are crazy reliable over time if you use them properly. I believe that's what I said.

.002 can actually be significant in this hobby. The difference between 1.026 and 1.028 for example is a big difference. Even the difference between 1.023 and 1.025 can be significant in terms of alkalinity and calcium levels. Plastic Hydrometers also don't have any kind of temperature compensation which means their accuracy can vary based on the water temp and the temperature of the water. I have one here that was brand new and came with a tank I acquired and it's - .005 off. That means that the hydrometer reads 1.025 when the actual water salinity was 1.030. I have another older one that reads very high. There is nothing accurate about hydrometers. They just aren't consistent from one to the next let alone at varying temperatures. Any experienced hobbyist will tell you that and if you want to be accurate which is critical in this hobby, then the only tool for the job is a properly calibrated refractometer that is calibrated with 35ppt refractometer calibration solution.

Also, in my experience, over time, the plastic arm tends to wear a bit causing them to become less accurate over time.

[Ron Reefman]

I think your concern for being accurate is just a bit over the top, but that's OK. It's definitely better to error on the side of being more careful than less. Although I think it's more important in big, high care tanks than what the average or beginner here needs.

As for the comment that a hydrometer plastic arm will 'wear a bit over time'... yikes! Adding some saltwater every week and then rinsing it out and the plastic will wear... seriously? I'll admit, I've only been testing mine for 5+ years and it hasn't changed at all.

[slief]

Originally Posted by Ron Reefman

I think your concern for being accurate is just a bit over the top, but that's OK. It's definitely better to error on the side of being more careful than less. Although I think it's more important in big, high care tanks than what the average or beginner here needs.

As for the comment that a hydrometer plastic arm will 'wear a bit over time'... yikes! Adding some saltwater every week and then rinsing it out and the plastic will wear... seriously? I'll admit, I've only been testing mine for 5+ years and it hasn't changed at all.

I say that based on my friend Jim's refractormeter but he uses his daily as that was his reference point for service customers. The arm was a bit worn and it also got sticky at the hinge point. When compared to my refractometeres, it was significantly off. The same can be said about the hyrdometers I have here.

I think we can agree that their accuracy is less than desired with a swing arm hydrometer and accuracy in your parameters is pretty important in my opinion. Especially one that impacts calcium, alkalinity & mg due to the nature of our salt mix. That .002-.003 can mean the difference between having low or high calicium, alk and mg depending on the salt mix. Thus, it's my contention that a refractometer and calibration solution should be first order of business for a new hobbiest. They are inexpensive and verifiably accurate. If you have a refractometer and can verify the margin of error on your hydrometer than great but for somebody new to the hobby who is looking for the proper tool for the job, a refractometer is the way to go.

[ericarenee]

I have to agree with Ron.


I also have a 30 year old glass hydrometer that is 100% accurate .Back before swing arm hydrometers came out for our hoby everyone said DO not buy a cheap swingarm they are wrong and will get worse over time...

Now its do not use swing arm because refractometer cost more and looks kewl..

Its like the argument i have with people in the trade i work in..

anyway

[slief]

Originally Posted by ericarenee

I have to agree with Ron.


I also have a 30 year old glass hydrometer that is 100% accurate .Back before swing arm hydrometers came out for our hoby everyone said DO not buy a cheap swingarm they are wrong and will get worse over time...

Now its do not use swing arm because refractometer cost more and looks kewl..

Its like the argument i have with people in the trade i work in..

anyway

I have no qualms with a glass hydrometer. When used properly, they can be very accurate. Swing arm ones are a different story. I am sure some are more accurate than others but to my knowledge, there is no documented comparison showing which are most accurate.

In the case of a fish only system, I have no issues using a swing arm one but in a reef, it's just not going to be accurate and there is a trickle down effect from that. When people have issues here, the first question is always "what are your parameters".. "Well, my salinity is somewhere between 1.023 and 1.027." This figuring a reasonable +/- .002 margin of error. I think most of us here would want to know their actual salinity with the least margin of error possible.

If I remember when I get home, I will dig out all my hydrometers (I have 2 or 3 different brands) and fill them up with some tank water to show how they all differ in results. Then use my refractometer to compare results. I've done it before for my friend Jim as that was the only way I could convince him to retire his beloved hydrometer in favor of a refractometer that I gave him. The differences were surprising.

[ericarenee]

Originally Posted by slief

I have no qualms with a glass hydrometer. When used properly, they can be very accurate. Swing arm ones are a different story. I am sure some are more accurate than others but to my knowledge, there is no documented comparison showing which are most accurate.

In the case of a fish only system, I have no issues using a swing arm one but in a reef, it's just not going to be accurate and there is a trickle down effect from that. When people have issues here, the first question is always "what are your parameters".. "Well, my salinity is somewhere between 1.023 and 1.027." This figuring a reasonable +/- .002 margin of error. I think most of us here would want to know their actual salinity with the least margin of error possible.

If I remember when I get home, I will dig out all my hydrometers (I have 2 or 3 different brands) and fill them up with some tank water to show how they all differ in results. Then use my refractometer to compare results. I've done it before for my friend Jim as that was the only way I could convince him to retire his beloved hydrometer in favor of a refractometer that I gave him. The differences were surprising.

I agree that each one will be off a bit. actually some are off a lot. The key to using swing arm hydrometers is to test them against a known good source. Find out how much they are off and adjust your mix accordingly .Just like Refractometers not all hydrometers Glass or swing arm are equal.The one i use is a older one by IO i think you can pull out the Arm and clean the whole thing..

I Agree there has been nothing that i have read where people using hydrometers causing random Results when cleaned and used properly.But i have read horror stories with People not knowing how or the need to calibrate there refractometer properly .
To me its the same as counting on reef controller probes to never fluctuate, I think every piece of equipment we use should be tested against something else.especially if the results seem out from what the Reefers experience is telling them .

I would like to see results of long term use of a hydrometer vs a refractometer. doing nothing but cleaning them both before and after each use. I guarantee the refractometer will be Inconsistent and the Hydrometer will still be accurate or off by the same % as it was from day one..

Thanks for the Discussion..

[Ron Reefman]

+1 for ericarenee

Steve just loves his high end stuff.

[Kadee]

I have yet to find a hobby tester or calibration fluid that does not have a disclaimer stating a margin of error. The main goal in testing at the hobby level is to monitor trends and make adjustments if necessary IMHO. I cannot imagine spending the amount of money necessary to purchase traceable instruments and calibration fluids to monitor your reef so that you can be relatively sure that you are getting exactly 1.026.

[slief]

Originally Posted by Ron Reefman

+1 for ericarenee

Steve just loves his high end stuff.

Nah.. I just trust my properly calibrated $25 refractometer more than I trust hydrometers with the swing arms. My refractometer always seems to match up with my conductivity probes where as I have yet to see a swing arm hydrometer that matches. I just don't see the logic is spending $10 on something that is widely recognized to be inaccurate when you can get a refractometer for $20 plus calibration solution for about $5 and at least have peace of mind that the numbers are accurate. And if we are recommending what to get for a new hobbiest, logic stands to reason that we would recommend the refractometer and not a hydrometer. Especially if one needs a properly calibrated refractometer to verify the margin of error on a swing arm hydrometer. And yes, I have hydrometer around here. I have tested them against my refractometer. I know how much they are off and use them from time to time as quick reference when mixing new water. As was noted in the comments above, if you know how much they are off, then great but I certainly wouldn't recommend one in place of a refractometer. That's all.


That said, I think your comment about expensive stuff is probably aimed more towards my other equipment. I've run cheap stuff in the past but I don't like failures. I've had my current main display for 25 years and it's been up and running here for 20 years now non stop since moving it to this house. I've never once had a return pump or power head failure on this tank. In fact, I have never really had any piece of equipment on this tank fail. I attribute that to buying high quality equipment. When your coral and live stock along with the rest of the system investment pushes the kinds of numbers it does on a system the size of mine, I can't rationalize buying based on price. Failures are unacceptable to me. Especially given the amount that I travel.


P.S. I'm Scott not Steve. I get that all the time though. Maybe I should change my user name.

[boxfishpooalot]

The most reliable and thus accurate method of measuring salinity is a floating glass hydrometer. A nist certified one is best and a diy salinity standard to verify accuracy. Also needs to be used with a thermometer as temperature is the biggest fluctuation in accuracy for salinity.

Refractometers can break and malfuction. Due to moving atc parts. Also inaccuracies exist as said above about calibration. Ive read three calibration solutions all read different. Thats why I recommend making your own.

[Skim]

What brand of Refractometer do you have?