Refractometers and salinity

DaveR11

DaveR11

Well-Known Member
I had lost a couple of Acros recently and wanted to check my parameters and I had worred my salinity might be off. So on visiting a new LFS today I got another refractometer to compare with mine. I keep my DT and QTs at 35 ppt with the temperature at between 25 and 26 centigrade. My original refractometer was by DD with the new one being unbranded.

So on getting home I tested the DT. The results were as follows:

DD - 35 ppt (as expected as the ATO works pretty well on my Red Sea 650).
Unbranded - 40 ppt. Yes 40!

I could not believe the difference. I calibrated both again using RO water and got the same result. So that really got me worried. Which one was correct? If the tank genuinely was 40 that might explain the loss of more sensitive corals. So I mixed up some new seawater - 1 litre according to Red Sea's instructions for the Coral Pro - 38g in 1 litre of water to give 35 ppt. The DD read it as 35 bang on the money and the unbranded as 40 ppt. So I know am pretty sure which one to believe.

When in the LFS I was told they use these unbranded refractometers for making up their water so I checked the water in the bags the new fish were in. I was told they kept their fish system at around 26 ppt. The DD machine read it as 23ppt so there was an even bigger difference in their salinity from mine....

Wondering now if I take the unbranded refractometer back as it is so far out....?
 
StirCrayzy

StirCrayzy

Well-Known Member
For reference, there was another thread recently on the same topic, and led me to wonder about my calibration. Mine is cheap BRS brand 7yrs old ish, and I've never adjusted since day 1.
So I dug out both my 35PPT fluid, and some fresh RODI and was 1 PPT lower than both values. Nothing to bother me, but I will note that I take great care to clean the prizm EVERY time I use it. There is a coating on it that must be maintained or you can have problems. I'm not sure exactly what those problems are, but might be worth looking into.
 
D

DaveK

Well-Known Member
You need to check the instructions that came with each refractometer. Some like to be calibrated with pure water, others like to be calibrated with a 35PPT fluid. If I was in doubt, I'd use the 35ppt fluid.

You really can not tell which refractometer is out. Either one could be off or they both might be off.

It's the old "A man with two watches never knows what time it is" kind of issue.
 
DaveR11

DaveR11

Well-Known Member
DaveK said:
You need to check the instructions that came with each refractometer. Some like to be calibrated with pure water, others like to be calibrated with a 35PPT fluid. If I was in doubt, I'd use the 35ppt fluid.

You really can not tell which refractometer is out. Either one could be off or they both might be off.

It's the old "A man with two watches never knows what time it is" kind of issue.
Click to expand...

Both manuals say calibrate with RO/DI water which I did. As I said I made up a litre of salt water as per the Red Sea instructions for 35ppt and the old DD one gave a reading of 35...
 
D

DaveK

Well-Known Member
This gets us into a different area. Salt loves to absorb moisture. This means that the only way to get SW to 35 ppt is mix the new SW and then measure it with a hydrometer or refractometer and then fine tune it by adding either more salt or more water until you get to 35 ppt.

After all that, if your new refractometer is way off and you can't calibrate it, it's time to return it to your LFS.
 
Paul B

Paul B

Well-Known Member
I don't use a refractometer for that problem and others. But what I do is take my $5.00 swing arm hydrometer to the airport, get on a plane to the place where my fish were collected. After I get there I rent a car so I can get to the sea. Then I rent a boat and go a few miles from shore, jump in the water with my $5.00 hydrometer and put a line on it with a permanent marker exactly where it reads. Then I get back on the plane, go to my house and check my water. Simple and accurate. :cool:

 
Oxylebius

Oxylebius

Well-Known Member
@nanoreefing4fun - good article.

I would be suspicious of the new unbranded model that you bought. I'd take it back. I have a milwaukee refractometer and four hydrometers (acquired since the 90s). I have to calibrate this brand of refractometer before each use. I use the milwaukee to calibrate the hydrometers so I can determine how off they are (not very, as long as you keep them clean and don't drop them).

BTW - have you tried to test your water with the refractometer in a dark room? Then see what the results show.
 
DaveR11

DaveR11

Well-Known Member
Paul B said:
I don't use a refractometer for that problem and others. But what I do is take my $5.00 swing arm hydrometer to the airport, get on a plane to the place where my fish were collected. After I get there I rent a car so I can get to the sea. Then I rent a boat and go a few miles from shore, jump in the water with my $5.00 hydrometer and put a line on it with a permanent marker exactly where it reads. Then I get back on the plane, go to my house and check my water. Simple and accurate. :cool:

Click to expand...

But Paul, I was expecting you had a supermodel jump in the water.....
 
Antics

Antics

Active Member
I've never had that issue but I've also never really thought to doubt my salinity in the past. Perhaps you could try a digital option like the Milwaukee MA887. A little pricey sure, but it sure is cool to use!
 
DaveR11

DaveR11

Well-Known Member
Oxylebius said:
@nanoreefing4fun - good article.

I would be suspicious of the new unbranded model that you bought. I'd take it back. I have a milwaukee refractometer and four hydrometers (acquired since the 90s). I have to calibrate this brand of refractometer before each use. I use the milwaukee to calibrate the hydrometers so I can determine how off they are (not very, as long as you keep them clean and don't drop them).

BTW - have you tried to test your water with the refractometer in a dark room? Then see what the results show.
Click to expand...

My regular LFS has just got a Milwaukee so definitely considering one now I know others I respect are using one....
 
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