Inconsistent Salinity Readings

[SurfTrack]

I have two refractometers AND a hydrometer and I am consistently getting different readings between the three. They range from 34 PPM to 36 PPM. It's driving me crazy. I clean and calibrate the refractometers every single use. I just don't know which device to trust. Is there a more accurate way to measure? I'll buy something new at this point.

Any ideas? Thanks!!

 

[RoanokeReef]

https://www.bulkreefsupply.com/high-precision-hydrometer-tropic-marin.html
Buy that and be done with it

 

[SurfTrack]

https://www.bulkreefsupply.com/high-precision-hydrometer-tropic-marin.html
Buy that and be done with it

Done.. Thanks!!

 

[RoanokeReef]

Done.. Thanks!!

Id also get something like this - Amazon product ASIN B00LV3ZFZ0

 

[Dogeatbird]

May I ask; why three? I would trust a refractometer versus a hydrometer.

Hydrometer require a large enough cylinder to float, both cylinder and hydrometer need to be clean, hydrometer must not have bubbles attached to outside surface, and be in no flow condition.(suspension)

Refractometers should be calibrated,(RODI) be viewed into decent light. If there is a diopter, verify it is set for your eyesight. Also note the refraction line should be crisp, and defined.

You could verify a reading by evaporating a known volume of test water and weighing the salt residue. Requires a calibrated scale , math, microwave, and small glass beaker.

Could also verify by mixing known volume of fresh salt water. Again weigh out dry salt mix to set volume of RODI Water. Example 100ml Water:2.5 grams Salt = SG 1.025.

Finally, Salinity measured in ppt is temperature dependent, Specific Gravity is a ratio of volume to weight. 34-36 ppt is not a big swing in concentration and may be an interpretative error, not a bad reading.

 

[SurfTrack]

May I ask; why three? I would trust a refractometer versus a hydrometer.

Hydrometer require a large enough cylinder to float, both cylinder and hydrometer need to be clean, hydrometer must not have bubbles attached to outside surface, and be in no flow condition.(suspension)

Refractometers should be calibrated,(RODI) be viewed into decent light. If there is a diopter, verify it is set for your eyesight. Also note the refraction line should be crisp, and defined.

You could verify a reading by evaporating a known volume of test water and weighing the salt residue. Requires a calibrated scale , math, microwave, and small glass beaker.

Could also verify by mixing known volume of fresh salt water. Again weigh out dry salt mix to set volume of RODI Water. Example 100ml Water:2.5 grams Salt = SG 1.025.

Finally, Salinity measured in ppt is temperature dependent, Specific Gravity is a ratio of volume to weight. 34-36 ppt is not a big swing in concentration and may be an interpretative error, not a bad reading.

I started with one new refractometer and when that one started giving slightly inconsistent readings, I picked up a hydrometer as a sort of "fail safe". Then I pulled out an old refractometer to triple check. They are all slightly different..

Yeah 34-36 ppt is not that much so I'm just letting it go for now. I'm going to pick up a more reliable testing device and go with that.

 

[NanoSteam]

https://www.bulkreefsupply.com/high-precision-hydrometer-tropic-marin.html
Buy that and be done with it

This is the way... solved all my salinity woes.

 

[Fish Fan]

The Tropic Marin hydrometer specifically is very good, I use one along with a 500 mL graduated cylinder as suggested above. Other hydrometers may be less accurate, and I really don’t care for the swing arm type, if that’s what you’ve been using.

I’d also suggest taking a look at this article from RHF on making your own DIY calibration solution since the store bought stuff can often give poor results. It’s easy to make your own with regular Morton’s iodized table salt and an accurate kitchen gram scale:
https://www.reef2reef.com/ams/reef-aquarium-salinity-diy-calibration-standards.956/
I hope this helps!

 

[Dogeatbird]

Ultimately it is your choice. Almost all equipment have error. Refractometers can be misaligned due to manufacturing error, dropped, impact, prism hazing. Hydrometer also have known error from weight, read error. Electric means also have known errors. Decide what is a best for you and evaluate based on your observations. Ultimately error whether mechanical, or statistical can be averaged out.

 

[Amstar]

this -- I use the tropic marine to get a "true" reading then I dial in my refractors and Hannah checker to the tropic marine - as well as cross check when I do calibrate them with solution back to the tropic marine -- hasn't steered me wrong and easy to do every month/two months

 

[exnisstech]

I've only been reefing 9ish years but I've never had a problem using a refractometer as long as it's calibrated with an accurate solution before each use. I use a TM hydrometer (verified accurate) to test each batch of new water. I then use that water to calibrate my two refractometers.

 

[rtparty]

A decent refractometer and good calibration solution is usually enough. Using 3 things will just end up where you are….frustrated

You don’t buy off the shelf calibration solutions either. They all suck. You make your own following RHF’s DIY recipe

 

[Sisterlimonpot]

I started with one new refractometer and when that one started giving slightly inconsistent readings, I picked up a hydrometer as a sort of "fail safe". Then I pulled out an old refractometer to triple check. They are all slightly different..

The point that needs to be made is that most hobbyists have this warped sense that theres a hobby grade piece of testing equipment that is accurate.

When someone says,

Buy that and be done with it

... it doesn't mean that's a more accurate solution, it just means someone, at some point used words and phrase in such a manner to convince you to trust a products results over another.

The take away is if you're looking for accurate results, you're not going to find it through hobby grade equipment. And that's not a bad thing. The goal is to pick one and use it. If a piece of equipment starts to fail, simply replace it and allow that to be your new standard.

 

[Dogeatbird]

It is your choice. There are refractometers for: Salinity, Glycol, Sucrose. Hydrometer also exist for a variety if solutions. Conductive methods also are available.

I would not recommend purchase of a new system. What variety and deviation is acceptable; only you, your goals, and your observations of your system will determine the answer you seek.

 

[DivingTheWorld]

This is the way... solved all my salinity woes.

It's the only thing I trust. Regarding the temperature required, it's 77 degrees F. But you can easily overcome this with Randy's temp corrections:

http://www.reefkeeping.com/issues/2004-07/rhf/
I have the calculation for the correction for my tank temp. I just turn off my pumps, float the hydrometer for 10 seconds to get the reading, then turn my pumps back on. Super easy, no cylinder required.

 

[Mr. Mojo Rising]

Pick a sword and live and die by that sword. Multiple tests usually give different readings and cause confusion and self-doubt.

 

[james frantz]

I have two refractometers AND a hydrometer and I am consistently getting different readings between the three. They range from 34 PPM to 36 PPM. It's driving me crazy. I clean and calibrate the refractometers every single use. I just don't know which device to trust. Is there a more accurate way to measure? I'll buy something new at this point.

Any ideas? Thanks!!

When using your refractor meter let it sit with the water droplets on it for about ten minutes before checking, and when calibrating do the same thing. I had a lot of the same issues myself, consistency is key.

 

[Dogeatbird]

Reminds me of poet, Robert Frost. “Two roads diverged in a yellow wood…”

Where each path leads, the bends, and snares, so each journey is unique.

Whatever choice made, the best of success.

 

[RoanokeReef]

... it doesn't mean that's a more accurate solution, it just means someone, at some point used words and phrase in such a manner to convince you to trust a products results over another.

Ok thanks for the wisdom. Just because you may be easily influenced by a salesman doesn't mean we all are.

The one thing I do agree with is pick one and use it hence " and be done with it" comment

 

[EnterName]

Can you tell me which devices you use?

The refractometers should give very similar readings but the hydrometer might be based on a different standard so you are measuring the density relative to freshwater's density at a different temperature than the refractometers do.

This means both readings are correct but the conversion from relative density to salinity differs between devices.

When you look through your refractometers you might see something like d20/20 which means the precision is best at 20°C and the result is the density relative to freshwater at 20°C. When your hydrometer has something like "SpGr. 25/4" on its neck, this means the precision is best at 25°C and the result is the density relative to freshwater at 4°C.

So the hydrometer will always show lower readings in this case, but using the correct conversion table for each device, you would get the same salinity.

.../4 refractometers are common in Europe and science as their readings are equivalent to the actual density of the liquid. In the US .../20 seems to be more common which makes it less confusing when comparing to refractometers which are nearly all 20/20 or 25/20 or when species in fahrenheit 68/68.