Refractometer a must?

falconut

falconut

New member
I've been in the hobby for over 5 years now. I still use a swing arm to test salinity. This week at one of our reef meetings, there were people that said you really need a refractometer. They were saying that the swing arms tend to read too high. My swing arm is and has been reading around 1.026, so now I'm wondering if by tank is too high. Is this true?
 
The swing arm hydrometer I have is significantly off. I calibrated mine with my properly calibrated refractometer, by putting a mark at the point for 1.0264. You need to make sure all the bubbles are removed to get a proper reading with a swing arm during the calibration and for every use.

When my swing arm reads 1.0225 it is actually at 1.0264. It is off by 0.004, which is not uncommon with the posts we have received from other hobbyists. :(
 
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I have two square box Seatest swing arms that I've been using for over 17 years now. (one I purchased a few years after the first when they first come out with full scale)
I rinse well after every use and I soak overnight in white vinegar once a week.
I "wet" the hydrometer well before using and then take two readings. If one is much different than the other I take a third and go with the two that reasonably match. If done properly, there is little chances of bubbles on the swing arm.
I lower the hydrometer slowly, top downward about 45° angle and slowly "scoop" the water into the hydrometer.
Once a year I check my hydrometers against a certified calibrated hydrometer and have never found them to vary after the initial calibration.
 
rayjay said:
I have two square box Seatest swing arms that I've been using for over 17 years now. (one I purchased a few years after the first when they first come out with full scale)
I rinse well after every use and I soak overnight in white vinegar once a week.
I "wet" the hydrometer well before using and then take two readings. If one is much different than the other I take a third and go with the two that reasonably match. If done properly, there is little chances of bubbles on the swing arm.
I lower the hydrometer slowly, top downward about 45° angle and slowly "scoop" the water into the hydrometer.
Once a year I check my hydrometers against a certified calibrated hydrometer and have never found them to vary after the initial calibration.
Click to expand...

You obviously have success with the hydrometer (17 yrs), but it just seems to me alot of 'maintenance' work with keeping your hydrometer on point. It seems that using a refractrometer is much easier....once calibrated, couple drops of SW and presto, your done. a quick targeted rinse with RO/DI and ready for next use. IMO, this free's up time for more of the fun stuff :beer:

'To each his own', I guess!!
 
Well first of all, I had these before refractometers were being used around here, and indeed I don't remember them even being discussed when I first got a computer in around 98.
Also, in the last 15yrs, I haven't had less than 10 sytems on the go so they get a lot of use for that as well as my brine shrimp growing operations not to mention the phyto and rots.
I have no way to know how many times I've knocked the hydrometers accidentally and just picked them up and used them again. At worst, once I had to super glue one that broke apart.
How does a refractometer stand up to accidents?
At the very least I would want it calibrated again.
Speaking of calibration, I've used my certified calibrated hydrometer to show other hobbyists that their refractometers are not always calibrated accurately.
One even disputed my readings and took his refractometer and his commercial calibration fluid to a company for testing and found his cf was out.
He then purchased two pkgs of their calibration fluid and went home and later that month found that both pakages, the same brand, differed.
The company that sold them didn't have an explanation other than they replaced one pack.
While they were out a little, which was correct and how much variation would there be from worst to best over time?
How about brand to brand variations?
At least with a certified calibrated hydrometer the only error is going to be user error if they have not be properly instructed on it's use.
As far as I'm concerned though, to be dead accurate is completely unnecessary as long as your readings are stable and you are in a reasonable range of NSW, unless you are doing hypo.
If whatever you have been using works for you, then I see no reason to change.
 
and Ray I agree :) I still have one I have had for more than 20 hears and it is right on the nose when checked against a $400 conductivity meter. The issue with the SeaTest swing arm is almost always "user" error :) And that is big fault, which pushes the refract to be a better device for measuring Salinity.

certified calibrated hydrometer

I could by a new car for all those I have broken :( If I still had tanks now I still would be using my SeaTest swing arm :D
 
I'm using a Tropic Marin glass hydrometer. I also use a calibrated refractometer. How do glass hydrometers stack up in terms of accuracy? Mine has always been pretty much dead on with my refractometer. Just curious. :)
 
They real question is does the slight variance make a difference in the health of the tank. I am pretty "ball park" with my swing arm and everything seems to do just fine for the last 5 years.
 
Wish I had calibrated my two coralife swing arms before I went 1.026; most corals showed no signs of stress, but the creatures that did, died slow deaths. I'm a stubborn Nørske American who believed refractometers needed to cost hundreds, and since my two swing arms measured consistently the same they were accurate.
 
I used a swing arm for years successfully. I think one key item is to rinse them with fresh water after each use. When salt water dries on the arm it leaves a crystal that will "attract" a small bubble the next time it is used and give a false higher reading. Make sure that each time you use it that you check for small bubbles adhering to the arm. If you see one bump it on the rim of the tank to get it off.

That being said, I use a refractometer now because I got a real good deal on one and it's pretty simple to use.
 
How do glass hydrometers stack up in terms of accuracy? Mine has always been pretty much dead on with my refractometer. Just curious.

Very well Kasey, as long as you are using a temp correction table for the hydro if using it at some other temp other than its cal temp of 77 F. NONE of these refracts will be accurate at low salinity but the hydro still will :)
 
Of course you dont have to have one. I think there great though, no bubbles to worry about and easy to verify there accuracy using calibration solution for reassurance. When you consider how much money you dump into your tank between equip. salt, filtration, livestock, etc its well worth the $40 for piece of mind IMO.
 
Boomer said:
How do glass hydrometers stack up in terms of accuracy? Mine has always been pretty much dead on with my refractometer. Just curious.

Very well Kasey, as long as you are using a temp correction table for the hydro if using it at some other temp other than its cal temp of 77 F. NONE of these refracts will be accurate at low salinity but the hydro still will :)
Click to expand...

Well that's good news! :p Thanks for the info Boomer!
 
I would phrase it: Hobby grade swing arm hydrometers can be used satisfactorily as long as you calibrate them first (usually one time is all that is needed) with a properly calibrated refractometer, since some (Deep Six Hydrometers for example) can be off significantly. ;)
 
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How about using 0 TDS water to calibrate?
For example i know my glass Hydrometer reads 0.001 in RO water.
So I know whatever the reading is... subtract 0.001.
The temperature was not 25 Celsius that should have been as stated on the hydrometer, but I will test again with 25C just to be sure what the reading is.
 
I used a swing arm for 4 years and was pretty accurate,but have changed to a refractormeter,I take it to my lfs and check it with the water he has made up to sell.The calibration fluid has varied alittle for me.
 
When I say swing arm I only stand behind the Instant Ocean/SeaTest, all other are crap. You can not calibrate a swing arm or a glass hydrometer, they have no adjustment to do that with. Instant Ocean/SeaTest do not need to be temp corrected for, as they are made out of thermal expansion plastic which auto temp corrects them. Most of the other swing arms are not. The Deep-Six is the worst thing there is :) But any of them can be tested against a mock seawater sample that is 35 ppt.

For most you are best off to go to the drug store and have the chemist make you one. Take some Morton's Iodized Salt, a empty container and RO/DI water with you. Have him add 3.714 grams of the salt to 996.256 ml of RO/DI water. Any hydrometer should read 1.0264 with this solution. If it is a floating hydrometer to test it or test you tank water to get temperature correction of any hydrometer cal temp go here.


Temp correction calculator
http://www.hamzasreef.com/Contents/Calculators/SalinityCorrection.php

1. Type in the reading you get on the floating hydrometer form the tank or bucket of water, say it reads 1.024
2. Type in the calibration temp of the hydrometer, say 77 F
3. Type in the water temp of the water you are testing, say 80 F
4. Hit calculate = 1.0245

Since our std is 35 ppt @ 1.0264 we are to low. IF we want that 1.0264 = 35 ppt then we need to raise the salinity but not to 1.0264 but 1.0259, which = 1.0264 =35 ppt if water was 77 F. I'll get soemthing added to this calculator so one can get that 1.0259 reading and not have to guess the Sg but typing it in till it reads 1.0259 = 35 ppt = std 1.0264/35 ppt in 77 F water.

If this is a tank then we use this to get the salinity we need.

Target Salinity Calculator
http://www.hamzasreef.com/Contents/Calculators/TargetSalinity.php



The temperature was not 25 Celsius that should have been as stated on the hydrometer

Who's hydrometer is it or where did you get it form. It may not be a 25 C but a 20 C or 15 C hydrometer
 
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