Salinity driving me nuts

[diverrad]

So I’ve been keeping reef tanks for about 25 years with rather good results. But now I had to go all out with fancy equipment just to make myself crazy.
I started a new IM fusion 40 crammed more gear than possible in to it and I’m letting it sit for a 3 months before I put anything in it. It will be all sps.
here’s my problem
apex salinity probe reads 37
hanna reads 32
reflectometer reads 1.27
I’m guessing the Hanna is off but I did calibrate it with the 35ppt solution. And when it reads the solution it does read it as 35.
the apex probe reads the same solution as 32
and the reflectometer reads the solution at 1.22
the Apex and the reflectometer seem to be getting the same reading but how can they see the test solution as less than 35 ppt?
all this makes me miss my old plastic hydrometer

 

[Sarcazian]

Tagging along. I have been getting mixed reading myself.

I have not personally calibrated my devices though .. solution(single BRS) came back higher on everything; however, every place I have purchased frags from has reported 34 or 35ppt.

Have you tried creating the salt solution mentioned on here? I did it once, but without a scale I have no confidence on the solution made.

 

[MONTANTK]

I would go with the refractometer since it’s the simplest of all your devices. I calibrate mine every time I use it and have never had issues since replacing my old one. I’ve read a lot of posts about hobbyists having issues with the apex salinity probe. I believe some have found success by mounting it upside down.

 

[diverrad]

I think you may be right. Though I believe that my problem might be the Hanna calibration solution. Both the apex and the reflectometer see it as low in the 31 range. Could it be that a whole box of new solution is that off?

 

[58e970b2-3f88-4897-87ba-5]

You can try making your own calibration solution:

http://www.reefkeeping.com/issues/2004-06/rhf/index.php

 

[diverrad]

You can try making your own calibration solution:

http://www.reefkeeping.com/issues/2004-06/rhf/index.php

Thank you for the link. Ok I will give this a shot.

 

[Dkeller_nc]

There are several reasons for your observations. One is that different instruments always give slightly different readings, it's just a matter of our expectations on how close those readings should be. A second is that both conductivity and refractive index vary with temperature. In the case of refractive index, it varies rather strongly with temperature in the range between a typical residential indoor temperature and a typical reef tank temperature.

Finally, the Apex salinity probe is known to have quite a bit of variation and is generally not used as the primary means of checking the absolute specific gravity of tank water. Instead, most owners set it up to alert them if there's a large change in conductivity (and hence specific gravity/salinity), such as caused by a malfunctioning ATO.

When you mention "Hanna", are you referring to the Hanna digital refractometer, or a Hanna conductivity pen/meter? If it's the digital refractometer (also available as a Milwaukee-branded unity), that is probably the one that I would trust over other instruments, as I've verified the accuracy of mine against carefully prepared laboratory refractive index standards, and it's off by no more than 0.001 RI units. That doesn't mean that my meter is completely representative of all of those meters, but it is a decent indication as to its accuracy.

 

[FishyFishFish]

Are you using the correct calibration fluids?

I’m not sure you can use the same solution for both the salinity meter and the refractometer.

 

[stanleo]

I just got an Apex and the salinity probe varies between 34 and 34.5 throughout the day. My refractometer reads 35. I go with it. You have been doing this a long time so I am sure you know that a stable salinity means more than an exact 35 ppt reading. If all three devices always read those numbers, then I wouldn't worry about it. not that 35 isn't ideal, but if its 33 or 37, as long as it is stable there, I am sure your tank is happy.

And people are right, I won't trust the salinity probe on the Apex except to tell me if there is a major event in salinity.

 

[Reef.]

I think you may be right. Though I believe that my problem might be the Hanna calibration solution. Both the apex and the reflectometer see it as low in the 31 range. Could it be that a whole box of new solution is that off?

the Hanna solution is not a salt solution so the other devices will not read it correctly, it’s a fluid designed to read conductivity at 35ppt, so you can’t add it to a refractometer and get a refractive index reading, you can use the refractometer calibration fluid on the Hanna though.

Buy a Tropic Marin hydrometer for your reference reader.

 

[CK00020]

Just like reef said, the hydrometer is really the only way. I have a Milwaukee that I use regularly and it stays in calibration well. I have fought with calibration fluids before as I have a bunch of other salinity testers some are more accurate than others. Making your calibration solution is really the only way to go. I will say the worst device I have for reading salinity is the icecap pen, it’s terribly frustrating and inaccurate.

 

[kaylajoy]

I have the same problem, my swing arm hydrometer is way off and the float hydrometer has a different reading from the refractometer...

What I've been doing is just testing the water that my livestock comes in. So far it's been very close to my tank on the refractometer so I'm not too worried. I also mixed up a homemade calibration solution and the refractometer was the most accurate one according to that.

Edit: I've read that some stores run super low salinity so I know this isn't always reliable, but it at least tells me which instrument is in the ballpark.

 

[diverrad]

Thank you for all your replies and suggestions.
I think the problem is and was the hanna pen salinity tester That came with my Hanna reef testing kit.
the apex is generally in the right zone. my reflectometer is spot on and I just had it tested at my lfs same readings.
so the Hanna is off by about 5 ppt. Way too much in my opinion. In to the growing junk pile it goes. Now to set up my apex trident I’m sure there will be posts with questions to follow lol.

 

[JosephM]

Go with TM floating hydrometer. It’ll confirm which is testing right and wrong. Never needs calibration and has a max deviation of 0.00001

 

[Randy Holmes-Farley Verified Community Expert]

Go with TM floating hydrometer. It’ll confirm which is testing right and wrong. Never needs calibration and has a max deviation of 0.00001

Ever check it? If not, how do you know it is accurate?

"a max deviation of 0.00001"

Don't know what that means, but I am highly skeptical you can distinguish 1.02601 from 1.02602.

Are you actually making that claim?

 

[JosephM]

Ever check it? If not, how do you know it is accurate?

"a max deviation of 0.00001"

Don't know what that means, but I am highly skeptical you can distinguish 1.02601 from 1.02602.

Are you actually making that claim?

They make that claim on their website. I can see with my eyes to the 0.0001. No I can’t distinguish to 0.00001.

 

[JosephM]

@Randy Holmes-Farley i can test it for you if you can do the math for me on how much table salt to add to 500ml of RO/DI water to make a 1.0255 calibration solution

 

[Reef.]

@Randy Holmes-Farley i can test it for you if you can do the math for me on how much table salt to add to 500ml of RO/DI water to make a 1.0255 calibration solution

I tested mine, I used 578.10g rodi water and 21.9g of table salt, my TM was 1.0265 with all the variables I was happy with that.

 

[JosephM]

I tested mine, I used 578.10g rodi water and 21.9g of table salt, my TM was 1.0265 with all the variables I was happy with that.

Yeah I love mine. It doesn’t jump around numbers like the Milwaukee tester I had before.