Thoughts on salinity/ SG

[Randy Holmes-Farley Verified Community Expert]

This article has helped me get a grasp on a lot of the salinity talk as im new to all of this. Give it a read and let me know what you think...

https://www.theaquariumsolution.com/specific-gravity-salinity-and-its-measurement

I think most of it is fine, and if you understand all of it, you are well ahead of most reefers.

I do not agree with everything listed there, however, such as the temperature as it relates to refractometers, most of which are ATC refractometers (automatic temperature compensation) and so should give results that are independent of temperature when properly calibrated.

 

[Randy Holmes-Farley Verified Community Expert]

I agree. What ive noticed ime is 1230 ppm limits the growth of corraline. But when its higher corraline grows faster. Like around 1350 to 1400 mag. So what im arguing here is that due to the accuracy of our testing that a failsafe could be to keep salinity higher with all the appropriate "electrolytes" too. So imo its better to keep the SG at 1.027-1.029 because if you do the math, it gives you some drift tolerances. Much like i prefer to keep alk at 9.7 dkh because it gives you +/- 2.7 dkh up or down. That room gives the error saftey net imo becaise 12.4 dkh isnt bad and 7 dkh isnt bad either if your kit reads higher or lower.

If it is magnesium you wan’t high, why push up everything else?

 

[Cory]

If it is magnesium you wan’t high, why push up everything else?

I agree it sounds strange. But the reason to push everything high is becaise i dont trust my equipments measures.

Ive got 3 devices. A fluval swing arm reads 1.0245, a sybon refractometer reads 1.025 and the Hanna digital seawater refractometer reads 1.026. It comes with a reference and it should be 1.025.

 

[Cory]

I think most of it is fine, and if you understand all of it, you are well ahead of most reefers.

I do not agree with everything listed there, however, such as the temperature as it relates to refractometers, most of which are ATC refractometers (automatic temperature compensation) and so should give results that are independent of temperature when properly calibrated.

Do you agree with the 20/20 in the eyepiece? That the calibration solution must be 20 C?

 

[Cory]

I don't know the nuts and bolts of how corals maintain their balance, but in animals like fish, the saltier the water they are in the more effort their kidneys have to perform in order to excrete the extra salt. The reverse happens in FW fish where they are constantly excreting water to hold on to their minerals/salts. Thanks to our friend osmosis, water likes to be balanced, organisms can't allow that to happen unchecked. Take humans. When you drink plenty of water it's not so hard for your kidneys to pass wastes, if you are dehydrated you still have to excrete that waste but your kidneys work much harder in order to do so without passing too much water. (drastic over simplifications)

In your air example, that also applies. It's much harder for us to live at high altitude. We have to produce more blood cells and I believe there are changes that happen in the lungs as well.

According to this quote the atompheric oxygen is the same but more dispersed. Im assuming nitrogen is also the same.

"The percentage of oxygen is the same at sea level as it is at high altitudes, which is roughly 21 percent. However, because air molecules at high altitudes are more dispersed, each breath delivers less oxygen to the body."

I agree with the kidney working harder but the question is whats an organisms tolerance to it? What can it handle. I havent seen anything suggesting 1.027 is harmful to fish kidneys. You?

 

[Randy Holmes-Farley Verified Community Expert]

Do you agree with the 20/20 in the eyepiece? That the calibration solution must be 20 C?

Nope. That makes zero sense. If it automatically corrects for temp differences in the reading, how can the temp of the standard matter at all ???

As a practical matter, the ATC will probably not be perfect, so calibration and measurement are best done at or close to the same temp, and I’d always calibrate with a reliable 35 ppt standard.

What the 20/20 might actually mean is that when properly calibrated (regardless of temp) that the specific gravity part of the scale is made so that it reads the density that the ppt reading on the scale would give for a seawater or brine sample at 20 deg C divides by the density of pure water at 20 deg C, which I would just call the specific gravity of the sample at 20 deg C.

Note that the specific gravity of seawater does not change much with temperature when the comparator pure water sample is at the same temperature.

 

[Randy Holmes-Farley Verified Community Expert]

According to this quote the atompheric oxygen is the same but more dispersed. Im assuming nitrogen is also the same.

"The percentage of oxygen is the same at sea level as it is at high altitudes, which is roughly 21 percent. However, because air molecules at high altitudes are more dispersed, each breath delivers less oxygen to the body."

I agree with the kidney working harder but the question is whats an organisms tolerance to it? What can it handle. I havent seen anything suggesting 1.027 is harmful to fish kidneys. You?

Plenty of the fish only people think their fish do better a somewhat lower specific gravity, like 1.021.

 

[infinite0180]

I think most of it is fine, and if you understand all of it, you are well ahead of most reefers.

I do not agree with everything listed there, however, such as the temperature as it relates to refractometers, most of which are ATC refractometers (automatic temperature compensation) and so should give results that are independent of temperature when properly calibrated.

Thanks Randy,
I actually have a BA in biology and i work in a lab. I found this article the other day but just realized i should probably check out some of your articles. Wow, there is ALOT here for me to read up on. I will be working my way through your stuff little by little! One quick question. My two bottles of 35ppt standard solution are not reading the same. I want to mix up a standard of my own at work using a scale that i know is calibrated correctly on a regular basis. Can i just take 3.65 grams of Mortons and 96.35 grams rodi or do i need a different salt? Thanks!

 

[Randy Holmes-Farley Verified Community Expert]

Thanks Randy,
I actually have a BA in biology and i work in a lab. I found this article the other day but just realized i should probably check out some of your articles. Wow, there is ALOT here for me to read up on. I will be working my way through your stuff little by little! One quick question. My two bottles of 35ppt standard solution are not reading the same. I want to mix up a standard of my own at work using a scale that i know is calibrated correctly on a regular basis. Can i just take 3.65 grams of Mortons and 96.35 grams rodi or do i need a different salt? Thanks!

Just NaCl (Morton's is fine), but the concentration depends on the device you are calibrating.

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2004-06/rhf/index.htm

Specific gravity (hydrometer):
3.714 weight percent sodium chloride solution = 35 ppt seawater equivalent = 1.0266 at 20 deg C

Conductivity
3.29 weight percent sodium chloride solution = 35 ppt seawater equivalent = 53 mS/cm

Refractometer
3.65 weight percent sodium chloride solution = 35 ppt seawater equivalent = 1.3394 refractive index