Refractometer @ swingarm SG testers

04-09-2004, 03:48 PM

Hydrometers give us the SG or specific gravity reading of our reef aquarium water.
SG swing arms hydrometers will vary with water temperature, as most are designed to work normally with 25 degrees C or 77 degrees F.
Now if you are testing water at a temperature that has NOT been calibrated for your swing arm then you will get a false reading.
Cold test water will give a false positive reading and warm test water will give a false negative reading.
Most swing arms claim to be .001 + - in accuracy.
As most reefers have used these types of hydrometers and have found them not to very accurate at all do to many factors involved when testing with them.
Swing arm hydrometers must be kept clean and free of any partials and air bubbles on the swing arm. The temperature must be at the temp it was calibrated for, which most of us in this hobby really don't have the time or effort to do this.
I personally have used 2 brand new SeaTest and 1 used 1 new deep 6 at the same time and got 4 different reading which all were below what I thought it should be. I have taken water in to a LFS and have had it tested with a refractometer and it was the same reading as my refractometer.
Now refractometers are known to be the most accurate SG testing devices. Most have ATC (automatic temperature compensating) which makes it a fine tool to use for us lazy reefers. Just apply 4 or 5 drops of tank water on to the lens and view the results. When finished wipe lens off with a damp towel. Most are .001 in accuracy.

Disclaimer: These are not the views of 3reef.com and or any other company that there equipment that was mentioned. These are only for discussion purposes with other reef aquarium users as an information tool and for discussion. This post was written by Nautilus aka David A. and are his views while using said equipment while doing his own water testing with his personal reef aquarium.

04-09-2004, 04:13 PM

This type of swing arm by SeaTest would be the unit I believe is the hardest to use.
1. You have to add water to the line at the top of the unit which some times is difficult to get it exactly right.
2.The way a person holds the unit must use a light grip to keep it level and if not the arm will sway up wards or down wards making it difficult for a accurate reading.
3. the Temperature must be exactly the same temperature it was calibrated for if not the reading with be false.

IMO if the unit is held incorrectly and you get a reading of say 1.022 then .001 + or - making it 1.023 or 1.021 and you have a known SG of 1.025 then this reading is caused by human error as most miss readings are.

Also if we don't take care of this type of unit by rinsing it after every use then we also take a greater chance of getting a greater miss reading.

The .001 accurate IMO is probably true when taken care of or close to it, but when you add in human error and not cleaning the unit the factor of getting miss reading is to great for me to deal with.

I had 2 new SeaTest units some time ago and if I remember correctly the reading were 1.021 and 1.023 this is within the manufactures accuracy of .001 and thats if it is calibrated correctly. Most of these units do not come with instruction on how to calibrate them and to me it would be to much of a hassle to do so.

IMO the lazy reefer as most are the refractometer is the way to go. it also has the same .001 accuracy but has a grander less chance of human error.
1. The ATC on a refractometer compensates for temperature so you don't have to worry.
2 Hold it in different angles does not produce false readings.
3 Clean with a damp cloth. easy as 1 2 3.

04-10-2004, 11:58 AM

Please post up some of your readings when you tested them against the refractometer. And which refractometer you did the testing with, and which swing arm you were using.

Thanks

Boomer · 04-10-2004, 12:30 PM

Dave

There is allot of incorrect stuff here.

SG swing arms hydrometers will vary with water temperature, as most are designed to work normally with 25 degrees C or 77 degrees F.
Now if you are testing water at a temperature that has NOT been calibrated for your swing arm then you will get a false reading

This is incorrect, this is for floating hydrometers. Many of the swing arms, i.e., SeaTest, Deep-SIX and I'm pretty sure the Usha, are temp comp. It is not an Oceanic SeaTest or a Marine Systems hydrometer. It is a Marine Environment hydrometer. The company name is right on the photo you posted . That swing arm has a registered trade mark name "Specific Gravity Tester". It iis not a AS but a poor copy of one. It is the only swing-arm that does not use thermal expansion plastic, that ADJUSTS fro temp compensation. As the water gets cold or warm the plastic expands or contacts at a know rate. That means you read the SG/Salinity direct off the unit. It is good for around 60-95 F. However, there is a real issue with the Deep-Six. They claim that you have to let it sit in water to become "seasoned" What ever the case may be, on independent test on the Deep-Six, against a know std, it has failed every time.

Swing arm hydrometers must be kept clean and free of any partials and air bubbles on the swing arm

Yes and that is an easy thing to do, but by far, most don't and that is the real issue of them giving incorrect readings

I personally have used 2 brand new SeaTest and 1 used 1 new deep 6 at the same time and got 4 different reading which all were below what I thought it should be. I have taken water in to a LFS and have had it tested with a refractometer and it was the same reading as my refractometer.

This is not thinkin' Dave, it is assuming. You really don't know if you refract is correct or not. If it is not tested against a std and RO/DI water is NOT a std. Thus, there should be know comment, as to who or which one is accurate or inaccurate. We see this all the time. Then there is the issue of accurac. Most are said to be within +/1 .001 SG, thi is refracts and hydrometers (to include $200 NIST hydrometers). If it or they fall with in that range, they will not replace it. 99.99 % of the time a NIST is exactly right on the noise, as far as hydrometers go. So is the Tropic Marine Hydrometer and the Hagen pseudo-lab hydrometers. Also, there is not a issue any more of temp compensation for floaters. I have a program/calculator done by a friend, that allows you to correct for temp. I also have his large Excel Spread Sheet one

Ok, the website is down or Simon has killed it, so I can't show it to day. Alll you do is type in the calibratiom temp, tank temp and observed SG -->Enter = x Salinity in ppt

http://www.wymag.org.uk/simon/salinityhr.htm

Now refractometers are known to be the most accurate SG testing devices

This is also incorrect. An EC Meter/ Conductivity meter is the most accurate. It is the std for Seawater analysis. Second, 99.99 % of all refracts are calibrated to NaCl NOT seawater. Seawater has a higher RI (Refractive Index )than NaCl . Which means, that right out of the box the refract is +/- .001 for seawater. If you know this and I and Randy have posted it many times, you can get it to its more normal +/- .001. You would want the refract to read .001 SG higher than you would normally want it. NSW is 1.0264 = 35 ppt NSW, so the refract needs to read 1.0274 =35 ppt NSW, IF it has ATC. If there is no ATC, you need to wait to let the water sample equilibrate with the refract and it is best to do it a 25 C/77F.

When finished wipe lens off with a damp towe

No, rinse off with RO/DI water then the damp towel or salt deposits will collect on the plate, just like they collect on the arm and pin of a swing-arm.

The issue on almost all of these refracts in this hobby, most are buying the same one, is where they came from and who makes them and how accurate are they really and how well does the ATC really work. They are made in China by Huake Instrument Co . They have NEVER been tested against a know std. That doesn't mean they are no good or less accurate than a SeaTest (properly cared for), they may be bette. I'm glad some people have stepped up a notch to a refract.

http://www.instrument-china.com/index.htm

Boomer · 04-10-2004, 01:08 PM

This type of swing arm by SeaTest would be the unit I believe is the hardest to use.

Not even, a floating hydrometer is the most difficult.This was in the other post, which hydrometer is the most difficult

1. You have to add water to the line at the top of the unit which some times is difficult to get it exactly right.

I have never found this to be a problem and it does not have to be exact

2.The way a person holds the unit must use a light grip to keep it level and if not the arm will sway up wards or down wards making it difficult for a accurate reading.

Easy enough, put on a table, that is why it has a flat bottom.

3. the Temperature must be exactly the same temperature it was calibrated for if not the reading with be false.

No, as before only the Marine Environments

IMO if the unit is held incorrectly and you get a reading of say 1.022 then .001 + or - making it 1.023 or 1.021 and you have a known SG of 1.025 then this reading is caused by human error as most miss readings are.

As I said, you are suppose to put it on a flat table/surface

Also if we don't take care of this type of unit by rinsing it after every use then we also take a greater chance of getting a greater miss reading.

Yes for sure and it needs to be soaked in vinegar for a few hours or so every month. I believe that is in the instructions, to include rinsing it

The .001 accurate IMO is probably true when taken care of or close to it, but when you add in human error and not cleaning the unit the factor of getting miss reading is to great for me to deal with.

There have been many tests on the SeaTest, against a std. Of all the tests I've seen, it is almost always a tad low, usually about 1.0255-1.0265, that would be a range of 34-35 ppt when it should read 35 ppt. Take note that a refract is off that much or more than that right out of the box, if you don't know the trick about RI, few do.

I had 2 new SeaTest units some time ago and if I remember correctly the reading were 1.021 and 1.023 this is within the manufactures accuracy of .001 and that's if it is calibrated correctly. Most of these units do not come with instruction on how to calibrate them and to me it would be to much of a hassle to do so.

There are no instruction for calibrating a SeaTest, it can not be calibrated

IMO the lazy reefer as most are the refractometer is the way to go. it also has the same .001 accuracy but has a grander less chance of human error.
1. The ATC on a refractometer compensates for temperature so you don't have to worry.
2 Hold it in different angles does not produce false readings.
3 Clean with a damp cloth. easy as 1 2 3.

Yes, refract have a lesser change of human error, for sure, even more so than a EC meter or NIST floating hydrometer or a SeaTest. I have been beating people for over 2 decades to get a refract or EC meter, but only recently have refracts come from China where they are so cheap. There has always been the cost thing. Remember though, this is the cheapest made refract that I know of in the world. Here are the real Cadillac ones. And they are way more than $100

http://www.atago.net/

http://www.kruess.com/
This is who the Chinese's are trying to copy, as the "Blue" color is their trade mark

My dream refract, for seawater and a house payment or loan to boot, if you want one
http://www.misco.com/Digital/salinity.html

NUGIO · 04-10-2004, 01:33 PM

That last one is very nice.I wish my house payment wasonly that much LOL!

04-10-2004, 03:09 PM

Boomer,

This is incorrect, this is for floating hydrometers. Many of the swing arms, i.e., SeaTest, Deep-SIX and I'm pretty sure the Usha are temp comp.
I have read information on 2 sites (other sites I never bookmarked... I knew I would need them for boomer...dang it) where both say the temp was effected when testing and that inculed seatest.

"I have owned three Aquarium Systems SeaTest Hydrometers in the past. The early series had less specific graduations, and is therefore less accurate. That one, however, cracked upon dropping, and I was forced to buy another. "
http://www.epinions.com/content_44790222468
and
http://www.practicalfishkeeping.co.u...?article_id=61

This is not thinkin' Dave, it is assuming.
How do we test it for a standard?

Now refractometers are known to be the most accurate SG testing devices ... maybe I should have said between swing arms and refractometers... oh I did it was in the thread title....

Which means, that right out of the box the refract is +/- .002 for seawater.
How can this be when you said it was a +.001. You stated that when reading a refracto meter then we must add .001 to that reading ie: 1.024 would be 1.025. So where do you get the +- .002 or the "-" part from?
Is this not just a +.001

No, rinse off with RO/DI water then the towel . Or salt deposits will collect on the plate, just like they collect on the arm and pin of a swing-arm.
This is what the manufacturer said to do in the instructions! wipe off with a damp cloth... any one else have instructions saying to do this?

04-10-2004, 03:34 PM

Boomer

This is what is advertized for my refractometer the Premium Blue Refractometer - RHS-10ATC

NEW IMPROVED MODEL - Our new Blue model has went through a few changes and is now better then before. It’s now a blue color with more heavy duty materials for longer lasting use. It includes a hard carrying case, screwdriver for calibration and dropper for easy place of water sample. The warranty is now 2 years (on new blue models) compared to 1 year before.PREMIUM BLUE SALINITY REFRACTOMETER with automatic temperature compensation
The RHS series are designed for testing the concentration of saltwater and brine. It's triple scale provides a direct reading of the specific gravity and concentration. (Parts per thousand) of salt in water and the RHS-10 proves itself invaluable for agriculture, food processing and wildlife management. this instrument is equipped with Automatic Compensation system making it ideal for field use.

Easy to use
Dual scale includes specific gravity and % per thousand
Automatic temperature compensation
Easily calibrated
Adjustable eyepiece
No batteries required
Carrying case included
Includes pipette and calibration screw driver
Range measurement:0-10%
Minimum division: 0.10%
Accuracy: 0.1%

How can they say it is for SG when it is really not?
Maybe you can get one and run all those tests for us and have a full report done which would make most of us a little happier ..... please

From website info=Take the reading where the boundary line of the blue and white intersect at the graduated scale. The scale will provide a direct reading (nD). USE THE SCALE ON THE FAR RIGHT FOR SPECIFIC GRAVITY. Clean the prism carefully using a damp soft cloth. DO NOT immerse refractometer in water. Please read the Operation Manual carefully before using the Refractometer.

Even when you look through the len it says SG so what gives here?
If you have time save the image and correct it with your insite for me as I like visuals *

NUGIO · 04-10-2004, 06:18 PM

Shouldnt that be far left for specific gravity?

Boomer · 04-10-2004, 07:17 PM

I have read information on 2 sites (other sites I never bookmarked... I knew I would need them for boomer...dang it) where both say the temp was effected when testing and that inculed seatest.

Your read that off this site and it is 100 % wrong. The guy is Michael Del Prete, owner of Marine Environment, aka MDPUSA on forums. He is an *** **** and refuses to debate me or Randy or Craig Bingman. He actually pretends we are not there asking difficult questions. Ask Mojoreef, Mike, he posts here.

http://www.aquacraft.net/sp0001.html

I don't know what you want me to say about those two website, please point it out, other than the first one gives it a high rating. Both sites have errors. Of course you are not suppose to drop it, same for your pH meter or refract, they are delicate instruments. I would be rich if I never had to replace all the 12" hydrometers where I broke the neck off *

Here is one error off the first site;

How It Works
The Aquarium Systems SeaTest Hydrometer, like any other hydrometer, tests for density or S.G.

It measures SG NOT density. Density and Sg ARE NOT the same thing. Many think it is. As temp rises from std or max density of seawater, density and Sg become further apart. By the time you get up into the upper 80's the SG and density are off by about 3 units i.e, 1.023 density and 1.026 Sg, using a 77 hydrometer.

Salinity
Most tropical marine environments have a salinity of about 33 parts per thousand (ppt), but some such as the Indo Pacific can be a lower at 32 ppt, and others like the Red Sea higher at 35 ppt. At 25° C that equates roughly to a specific gravity of about 1.023-1.025.

Most **reefs, go look, are at 35 ppt. The Red Sea is almost 40 ppt. You want your hydrometer to read about 1.0264 and the refract to read about 1.0274 at around 82 F. The *NSW salinity, in any book on this planet, is 35 ppt and is what most coral reefs are.

The common error often found on the net from and from the other website

To make up salt water to suit most reef organisms add about 33g of salt to each litre of water to get a specific gravity of around 1.023 when it’s tested at 25°C.

This gives you 31 ppt and we want NSW, which is 35 ppt or 1.0264 Sg. We are talking reef tanks and not FOT tanks.
Sure there are reefs with lower and higher salinity but we are trying to get people all at the same salinity. Check my other post from the other day, on the Law of Equal Proportions. If your reef tank was 31 ppt I would not be telling you to keep your Ca at 400 mg / l, it would be around 375 mg / l and I would tell you a lower Alk and Mg etc, etc,. See the problem ?

How do we test it for a standard?

Here's a compilation of salinity standards that people can make out of dry table salt and water (using a good balance):

If you want an S=35 standard for specific gravity, try 3.7 weight percent NaCl in water at 20 deg C

If you want an S=35 standard for refractive index, try 3.6 weight percent NaCl in water

If you want an S=35 standard for conductivity, try 3.17 weight percent NaCl in water

How can this be when you said it was a +.001. You stated that when reading a refracto meter then we must add .001 to that reading ie: 1.024 would be 1.025. So where do you get the +- .002 or the "-" part from?
Is this not just a +.001

Correct, but few people know about the add on, I stated that, so that by itself is .001, then there is the accuracy of refract itself of .001, so .001 +.001 = .002, which means the refract out of the box **without the add on can be off by .002. Look at it this way. It reads 1.025, but tested it should 1.026 with a std NaCl, where seawater should be at 1.027. That is .001 to low from std, now we are using it is seawater, another .001 to low, nothing to do with accuracy, so it should read 1.027 *However, ** it could read 1.025, with out the add on. So your salinity showing without the add on will make you think you are at 33 ppt and not 35 ppt. If you corrected it for Seawater it would be 34 ppt, the refract itself is reading low, just like a SeaTest can read to low. The Seatest should read 35 ppt but it reads 34 ppt, it is in error as is the refract. Now if the refract was right on the noise, then the error is only the .001 add on correct ? Don't forget that refract, like a SeaTest, is +/- .001. Now, if the refract read .001 to high, without the add on, the refract would be right where NSW is 1.0264 and you would not need the add on.You are dealing with Seawater and not NaCl, so who cares, thus it is set to NSW Sg by error and you would want it to read 1.026 and not 1.0274 - high 001 error = 1.0264. No add on needed.

This is what the manufacturer said to do in the instructions! wipe off with a damp cloth... any one else have instructions saying to do this?

That does not mean rinse it under the sink. An eye-dropper with some RO/DI or Distilled water to rinse off any salts. The damp cloth may not get them all. It is called being safe. It is std practice to rise instruments of with RO/DI or Distilled water before use. Same with test kit vials.

oh I did it was in the thread title....

Yeah I know, but not in News thread

Your swing arm you mentioned is the hardness to get the most accurate reading from because of the way it was designed.

Taken as the hardest of all units to use i.e., *refracts, floaters, EC meters,etc..