Inconsistent Salinity Readings

[SurfTrack]

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.

Both refractometers are "saltwater d20/20"

This is a good point...I had not considered this

 

[SurfTrack]

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.

This seems like the way to go. I just got back into the hobby and have a three week old 15g rimless cube. Years ago, I 112g had a Red Sea Reefer with a built in 20g ATO reservoir. I'm not used to such a small system.

I am genuinely shocked by how much water evaporates from the 15g (0.5-1g/day)...I never had salinity doubts with my larger setup. I'm currently looking for a good ATO system. The only livestock I have now are two clowns which can handle the slight salinity fluctuations, but I need to get it sorted before I get any CUC or corals..

 

[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.

Both refractometers are "saltwater d20/20"

This is a good point...I had not considered this

Okay then at least the refractometers should give equal readings.

If you have the AquaMedic DensiMeter (65905), JBL Hydrometer (6140800) or TropicMarin Hydrometer (51001) it's 25/4. Double check the product code as some manufacturers sell 20/20 versions as well. Other devices are very likely 20/20.

 

[254633]

Its expensive as all get out but I've had a lot of success with my Milwaukee digital

Ive had it for about a year and it always reads 1.000 with distilled water.
Ive heard it can be a bit off with the exact number for salt, but if it is its consistently off so measurements are repeatable. Everything is still alive so it must be close to correct haha

The price is a big pill to swallow but I cant tell you how nice it is to have instant salinity readings that I can trust(so far)

Amazon product

 

[Fish Fan]

Its expensive as all get out but I've had a lot of success with my Milwaukee digital

Ive had it for about a year and it always reads 1.000 with distilled water.
Ive heard it can be a bit off with the exact number for salt, but if it is its consistently off so measurements are repeatable. Everything is still alive so it must be close to correct haha

The price is a big pill to swallow but I cant tell you how nice it is to have instant salinity readings that I can trust(so far)

Amazon product

I love my Milwaukee digital refractometer! No, it's not the most accurate way to measure salinity, but it is hands down the most convenient option for sure

 

[Dogeatbird]

step back and look at what is being offered to the publisher of this thread. Is it really necessary to be dead certain. Statistical noise, I.e. variant in reading, is common in data collection, analysis, and practice. Simple variations in the density of water from 4-25•C/39-78•F accounts for this noise.

So use what you have, Refractometers, Hydrometer, Digital Refractometer, Conductivity, a scale and known volume of water. Be aware that regardless of method,measurement apparatus, there will be a variance. Attempt to adhere to your protocol , and you will have success.

If you still are stressed about your data, then consider a second opinion, I.e LFS, local reef club, friend who has a different method. Just be aware it is a single,different, point of data. All methods, even those employed at research universities contend with noise.

 

[Sam7]

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,

... 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.

We have a Winner

 

[vijay_06]

I have been using a Tropic Marine Hydrometer. Based on what I read on the internet, it will give you reliable measurement.