Salinity why 1.025 not 35ppt

[trigon 350]

Hi, fellow reefers.

Im in the united kingdom and have been reefing for 2.5 years now.

This is a four part statement, finding or question.

1) when I first started I always found my salt mixes of various brands never had the mag, calc and kh as the bucket stated.
All the responses I got had always been the same we test at 35ppt, here is the certificate for your bucket.
As far as I was concerned I calibrated my refractometer at 20c many many times with r.o water, so definitely wasn't an issue my end.
I had taken my water to several fish shops who also confirm my salt water was at the recommended 1.025 .

2) months later I was ordering some bits and had seen a 35ppt calibration fluid for refractometers.
A bit confused as the 3 refractometers that I had owned all say to zero with r.o water at 20c ( i had tried 25c aswell ).
Anyway, I placed the order.
I used the 35ppt solution into my r.o water calibrated refractometer and I was registering 1.025???. So very confused.
I then calibrated my refractometer with the 35ppt solution. Now I added a few drops of r.0 water and result was at least 2ppt below the zero line!
So with this in mind, I then mixed a fresh bucket of salt to the newly calibrated refractometer to 35ppt.
This resulted in the extact calc,mag, and kh as stated on the bucket.....

WINNER

Now what has confused me even more is that not one of the salt companies replied in their emails asking if I had used a calibration solution, and also that I know all my local fish shops also use r.o water to calibrate their refractometers, even worse one of them actually gave me a refund for the bucket....

3) I am seriously wondering now in how many people are mixing salt and at nowhere near the salinity they think they are.
I started testing the water from places I was buying corals from, all say they keep water at 1.025, i test it at 1.023...

4) does this also mean that if im using the calibration fluid thats it irrelevant at what temperature i use, as long as at the given time the 35ppt is calibrated at the same temperature as the water to be tested?

The Predicament .
I had started keeping my reef at 35ppt.
I have had many icp tests and this always come back to my 35ppt measured level.

So I have had several different brands of refractometers, all with the same results.

This raises a few questions.

Can this many local shops really be all getting this wrong?

How many hobbiests are aiming for 1.025 and are actually at 1.023 or less?

The main question that I really can't understand is why I'm always being recommended 1.025 and not 1.0264 35ppt?

Where has the 1.025 even come from.

Should we aim for 1.0264 or 1.025.

Im really not concerned about the elements as I dose all, this is literally about the salinity not the changes in elements that this brings.

Thanks for reading, will be interested to hear people opinions on this.

 

[Randy Holmes-Farley]

A few comments...

1. Reef tanks do not seem to require any particular salinity and tanks seem to work great over a significant range. That range does seem to include a sg of 1.025 as well as higher levels, up to at least 1.027. The OK range may be much wider, as long as some critical components are maintained.

2. I think there has sometimes been confusion on the part of some folks in the past about density vs specific gravity, and historically that may have led some folks to inadvertently use or recommend a lower salinity. The density of 35 ppt seawater at normal tank temps (say, 77 deg F) is 1.0234 g/cm3. I think some folks quoted that value or similar values and either did not understand it was different than specific gravity, or others reading or hearing it made that misunderstanding.

3. All devices that hobbyists use have a temperature dependence to the results they produce that is NOT reflective of the actual change (if any) in specific gravity (very small change with temp changes) or salinity (no change with temp changes). Many of these devices try to autocorrect for their own temp effects, including most refractometers (always called ATC refractometers) and conductivity meters. Swing arm hydrometers also account for temp changes, but floating glass hydrometers DO NOT and need a manual correction.

4. If you are using a perfect ATC refractometer with a perfect standard, it will not matter what temp you calibrate or measure at, as long as you are within its range of proper temp correction. Some refractometer manufacturers get this wrong, and claim a particular temp is needed, but that makes no sense. That said, if you calibrate and measure at the same temp, you do not need to make any assumptions that the refractometer is doing the ATC correction accurately.

5. If you are using a brine refractometer (which many in the hobby are), and assuming it is perfectly made and perfectly calibrated with RO water, it will necessarily be slightly off when measuring seawater because brine is not the same as seawater, but resellers of such refractometers neglect to mention that (probably do not know it). If you calibrate it with a perfect 35 ppt standard, it will read 35 ppt and values close to that correctly (but will then read ro water inaccurately, but that's no concern).

 

[Dread Pirate Dave]

A few comments...

1. Reef tanks do not seem to require any particular salinity and tanks seem to work great over a significant range. That range does seem to include a sg of 1.025 as well as higher levels, up to at least 1.027. The OK range may be much wider, as long as some critical components are maintained.

2. I think there has sometimes been confusion on the part of some folks in the past about density vs specific gravity, and historically that may have led some folks to inadvertently use or recommend a lower salinity. The density of 35 ppt seawater at normal tank temps (say, 77 deg F) is 1.0234 g/cm3. I think some folks quoted that value or similar values and either did not understand it was different than specific gravity, or others reading or hearing it made that misunderstanding.

3. All devices that hobbyists use have a temperature dependence to the results they produce that is NOT reflective of the actual change (if any) in specific gravity (very small change with temp changes) or salinity (no change with temp changes). Many of these devices try to autocorrect for their own temp effects, including most refractometers (always called ATC refractometers) and conductivity meters. Swing arm hydrometers also account for temp changes, but floating glass hydrometers DO NOT and need a manual correction.

4. If you are using a perfect ATC refractometer with a perfect standard, it will not matter what temp you calibrate or measure at, as long as you are within its range of proper temp correction. Some refractometer manufacturers get this wrong, and claim a particular temp is needed, but that makes no sense. That said, if you calibrate and measure at the same temp, you do not need to make any assumptions that the refractometer is doing the ATC correction accurately.

5. If you are using a brine refractometer (which many in the hobby are), and assuming it is perfectly made and perfectly calibrated with RO water, it will necessarily be slightly off when measuring seawater because brine is not the same as seawater, but resellers of such refractometers neglect to mention that (probably do not know it). If you calibrate it with a perfect 35 ppt standard, it will read 35 ppt and values close to that correctly (but will then read ro water inaccurately, but that's no concern).

Thanks for the detailed explanation! I've wondered about the differences between these two myself.

I just use a Hanna checker that supposedly temp compensates. I do calibrate it monthly. I"m not sure how accurate it is but I figure as long as things are consistent it'll be fine.

 

[trigon 350]

A few comments...

1. Reef tanks do not seem to require any particular salinity and tanks seem to work great over a significant range. That range does seem to include a sg of 1.025 as well as higher levels, up to at least 1.027. The OK range may be much wider, as long as some critical components are maintained.

2. I think there has sometimes been confusion on the part of some folks in the past about density vs specific gravity, and historically that may have led some folks to inadvertently use or recommend a lower salinity. The density of 35 ppt seawater at normal tank temps (say, 77 deg F) is 1.0234 g/cm3. I think some folks quoted that value or similar values and either did not understand it was different than specific gravity, or others reading or hearing it made that misunderstanding.

3. All devices that hobbyists use have a temperature dependence to the results they produce that is NOT reflective of the actual change (if any) in specific gravity (very small change with temp changes) or salinity (no change with temp changes). Many of these devices try to autocorrect for their own temp effects, including most refractometers (always called ATC refractometers) and conductivity meters. Swing arm hydrometers also account for temp changes, but floating glass hydrometers DO NOT and need a manual correction.

4. If you are using a perfect ATC refractometer with a perfect standard, it will not matter what temp you calibrate or measure at, as long as you are within its range of proper temp correction. Some refractometer manufacturers get this wrong, and claim a particular temp is needed, but that makes no sense. That said, if you calibrate and measure at the same temp, you do not need to make any assumptions that the refractometer is doing the ATC correction accurately.

5. If you are using a brine refractometer (which many in the hobby are), and assuming it is perfectly made and perfectly calibrated with RO water, it will necessarily be slightly off when measuring seawater because brine is not the same as seawater, but resellers of such refractometers neglect to mention that (probably do not know it). If you calibrate it with a perfect 35 ppt standard, it will read 35 ppt and values close to that correctly (but will then read ro water inaccurately, but that's no concern).

Thats perfect, thankyou very much.

 

[Randy Holmes-Farley]

Thanks for the detailed explanation! I've wondered about the differences between these two myself.

I just use a Hanna checker that supposedly temp compensates. I do calibrate it monthly. I"m not sure how accurate it is but I figure as long as things are consistent it'll be fine.

Many folks think it reads low when using the Hanna fluid. You might make a diy and try that to see how it comes out.

Reef Aquarium Salinity: DIY Calibration Standards

Reef Aquarium Salinity: DIY Calibration Standards By Randy Holmes-Farley One of the most important issues facing marine aquarists is providing a suitable environment for their aquaria's inhabitants. Among the important properties for a marine...

www.reef2reef.com

 

[Jamie9]

I struggled for a while with my Hanna salinity checker. Sometimes I'd calibrate it and it would seem to be spot on, other times it would clearly be off. Or I'd get it calibrated well and my son would accidentally hit the cal button and it would get thrown off. I do get a sense that the provide calibration packets have more variability than I would like. There is Randy's calibration recipe that can help with that.

But, what I finally did is just get the TM high precision hydrometer. I use that to keep my tank at 1.026 or thereabouts. Because my tank is small I can't use that on my water change prep unless I'm doing 30% or so (It requires maybe 15" oof water depth. But what I do is use my Hanna checker to make sure my water change is the same as the tank, and I can use it to easily check throughout the week that things are holding constant. So in other words, I use the TM hydrometer for accuracy...and I use the Hanna checker for convenience to monitor trends...knowing that my Hanna Checker is not super accurate most of the time.

 

[Ef4life]

Tropic Marin hydrometer and a 500ml graduated cylinder is what I use to check salinity

 

[Jamie9]

Tropic Marin hydrometer and a 500ml graduated cylinder is what I use to check salinity

Yeah, I really ought to get myself a graduated cylinder for that. Always one more thing to find a spot for!

 

[Randy Holmes-Farley]

..and I use the Hanna checker for convenience to monitor trends...knowing that my Hanna Checker is not super accurate most of the time.

If you make a liter of a standard, it will last forever and you can always match the Hanna to that. I dip my conductivity probe into it every time to check it. Rarely do I bother to recalibrate it. If it has drifted a little bit, i just do a manual correction.

I know the standard is 53 mS/cm. If it reads 52.5, I just take any tank water reading and correct it by a factor of 53/52.5 = 1.0095, so a reading of 52 becomes a true reading of 52.5 mS/cm. If you have a device reading in other units, you can do the same with those units, though with sg, you ignore the leading 1.

 

[skey44]

Tropic Marin hydrometer and a 500ml graduated cylinder is what I use to check salinity

Will add at 77F as Randy mentioned. You will need to correct for temperature variation if not at 77.

 

[Randy Holmes-Farley]

I personally would not assume any device is accurate, including the TM hydrometer, without verifying it. When i checked the smaller TM hydrometer I had in the past, it was accurate, but that does not mean all will be. Also, be sure you are reading it correctly if you use a floating hydrometer, and provide a temp correction, if needed.

This picture is a Tropic Marin hydrometer showing the meniscus rising to about 1.0260, but the actual reading is about 1.0265.

 

[KrisReef]

I personally would not assume any device is accurate, including the TM hydrometer, without verifying it. When i checked the smaller TM hydrometer I had in the past, it was accurate, but that does not mean all will be. Also, be sure you are reading it correctly if you use a floating hydrometer, and provide a temp correction, if needed.

This picture is a Tropic Marin hydrometer showing the meniscus rising to about 1.0260, but the actual reading is about 1.0265.

Blasphemy!

Any help to explain the impact of surface tension on the readings of these floating instruments?

 

[Randy Holmes-Farley]

Blasphemy!

Any help to explain the impact of surface tension on the readings of these floating instruments?

The effect of surface tension is on the nature of the meniscus. The higher it climbs, the more it pulls the device down.

I do not know what sort of meniscus they assume in manufacturing, which is a good reason to validate them. Keeping it clean may also help standardize the meniscus.