Thoughts on salinity/ SG

[Cory]

Im thinking if seawater is naturally 1.0264 SG or 35 ppt, then isnt 1.027 better than 1.026 because low suggests limiting things and higher suggests abundance rather than scarcity? For example what would magnesium be at 1.026 rather than 1.027. At 1.025 isnt magnesium getting critcal. And if you consider accuracy of our test equipment being 1%-2% then it can be even worse.

 

[WV Reefer]

Im thinking if seawater is naturally 1.0264 SG or 35 ppt, then isnt 1.027 better than 1.026 because low suggests limiting things and higher suggests abundance rather than scarcity? For example what would magnesium be at 1.026 rather than 1.027. At 1.025 isnt magnesium getting critcal. And if you consider accuracy of our test equipment being 1%-2% then it can be even worse.

I don’t really think that deeply about it.......Consistency is usually the key rather than the actual numbers.

I’m sure there are reef scientists that will chime in on this question.

 

[Randy Holmes-Farley Verified Community Expert]

Im thinking if seawater is naturally 1.0264 SG or 35 ppt, then isnt 1.027 better than 1.026 because low suggests limiting things and higher suggests abundance rather than scarcity? For example what would magnesium be at 1.026 rather than 1.027. At 1.025 isnt magnesium getting critcal. And if you consider accuracy of our test equipment being 1%-2% then it can be even worse.

The salinity inside cells is lower than seawater. The more salt is outside, the more energy that organisms have to spend maintaining that balance.

 

[Randy Holmes-Farley Verified Community Expert]

Im thinking if seawater is naturally 1.0264 SG or 35 ppt, then isnt 1.027 better than 1.026 because low suggests limiting things and higher suggests abundance rather than scarcity? For example what would magnesium be at 1.026 rather than 1.027. At 1.025 isnt magnesium getting critcal. And if you consider accuracy of our test equipment being 1%-2% then it can be even worse.

There are fundamental unanswered questions here. If you take NSW, and remove just NaCl, salinity declines but everything these remains unchanged. Might that be good?

Reefers approximate this test when maintaining parameters and also have lower salinity.

 

[chipmunkofdoom2]

For example what would magnesium be at 1.026 rather than 1.027. At 1.025 isnt magnesium getting critcal

It's much easier to use salinity instead of specific gravity for these types of calculations. 1.025 SG = 33.2, 1.026 SG = 34.5 ppt and 1.027 SG = 35.8 ppt.

Let's assume that magnesium is 1,350 ppm at 34.5 ppt. 35.8 ppt is about 3.7% higher than 34.5 ppt. So, if all the minerals in the seawater scaled linearly, then the magnesium would rise to about 1,400 ppm. If we go the other way and assume you diluted your sample, 33.2 is about 4% lower than 34.5 ppt. So, if all minerals scaled at the same rate, magnesium would drop to around 1,300 ppm.

Either way, magnesium increasing to 1,400 ppm or decreasing to 1,300 ppm is not critical.

 

[Cory]

The salinity inside cells is lower than seawater. The more salt is outside, the more energy that organisms have to spend maintaining that balance.

More energy as in calories? Wouldnt a reef fish or coral have been adapted to "saltiness" and thus not be affected by these minimal differences in salinity but where we see things suffer most is when these "electrolytes" like cal mag and potassium get low. And since sodium and chloride make up most of this energy this shouldnt be a concern no? What im trying to say is spending less energy seems to say there is a flaw in their biology and they haven't sufficiently adapted to their salty environment and thus lower salinity is somehow bettter than higher. These "electrolytes" are what we maintain for proper health because they decline. We wouldnt think the same for the air we breathe no? Like its better to live in 60% nitrogen atmosphere instead of 80% because we spend less energy. Sorry just trying to understand

 

[Cory]

It's much easier to use salinity instead of specific gravity for these types of calculations. 1.025 SG = 33.2, 1.026 SG = 34.5 ppt and 1.027 SG = 35.8 ppt.

Let's assume that magnesium is 1,350 ppm at 34.5 ppt. 35.8 ppt is about 3.7% higher than 34.5 ppt. So, if all the minerals in the seawater scaled linearly, then the magnesium would rise to about 1,400 ppm. If we go the other way and assume you diluted your sample, 33.2 is about 4% lower than 34.5 ppt. So, if all minerals scaled at the same rate, magnesium would drop to around 1,300 ppm.

Either way, magnesium increasing to 1,400 ppm or decreasing to 1,300 ppm is not critical.

I like your math. But nsw is not 1350 magnesium. Its usually 1280. Im curious what those numbers get to from 1280 ppm magnesium. Im guessing that mag would be around 1230 which imo is getting low.

 

[chipmunkofdoom2]

I like your math. But nsw is not 1350 magnesium. Its usually 1280. Im curious what those numbers get to from 1280 ppm magnesium. Im guessing that mag would be around 1230 which imo is getting low.

If we're talking natural levels, then carbonate alkalinity would be around 7 dKh, maybe lower. Calcium would be just a bit over 400 ppm. If the salinity was artificially lowered by adding freshwater or raised by evaporating water, then the alkalinity and calcium would increse or decrease in the exact same proportions as magnesium would.

If the ratios of calcium/alkalinity to magnesium stay the exact same, why would 1,230 ppm magnesium be too low?

 

[OriginalUserName]

More energy as in calories? Wouldnt a reef fish or coral have been adapted to "saltiness" and thus not be affected by these minimal differences in salinity but where we see things suffer most is when these "electrolytes" like cal mag and potassium get low. And since sodium and chloride make up most of this energy this shouldnt be a concern no? What im trying to say is spending less energy seems to say there is a flaw in their biology and they haven't sufficiently adapted to their salty environment and thus lower salinity is somehow bettter than higher. These "electrolytes" are what we maintain for proper health because they decline. We wouldnt think the same for the air we breathe no? Like its better to live in 60% nitrogen atmosphere instead of 80% because we spend less energy. Sorry just trying to understand

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.

 

[JimWelsh]

But nsw is not 1350 magnesium. Its usually 1280.

That is only true when calculating "PPM" as mg/Kg (w/w). Reef test kits typically measure things in mg/L (w/v). You don't take a given weight of your sample; you take a given volume. At room temperature, that 1280 Mg value for NSW becomes 1320 PPM. At typical reef temperatures (e.g., 25C), it becomes more like 1314 PPM.

 

[Cory]

If we're talking natural levels, then carbonate alkalinity would be around 7 dKh, maybe lower. Calcium would be just a bit over 400 ppm. If the salinity was artificially lowered by adding freshwater or raised by evaporating water, then the alkalinity and calcium would increse or decrease in the exact same proportions as magnesium would.

If the ratios of calcium/alkalinity to magnesium stay the exact same, why would 1,230 ppm magnesium be too low?

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.

 

[Cory]

That is only true when calculating "PPM" as mg/Kg (w/w). Reef test kits typically measure things in mg/L (w/v). You don't take a given weight of your sample; you take a given volume. At room temperature, that 1280 Mg value for NSW becomes 1320 PPM. At typical reef temperatures (e.g., 25C), it becomes more like 1314 PPM.

Are you saying our test kits reading fluctuate based on temperature necause volume fluctuates based on temp? Im thinking icp tests wouldnt be effected by this. Whats your opinion on the salinity we should keep?

 

[JimWelsh]

Are you saying our test kits reading fluctuate based on temperature necause volume fluctuates based on temp? Im thinking icp tests wouldnt be effected by this. Whats your opinion on the salinity we should keep?

To the degree that temperature affects the density of tank water and/or test kit reagents, then of course. We are measuring these liquids by volume, and as the density of the liquids changes, so does the mass contained within that volume.

There is nothing magical about ICP that makes it immune to the basic laws of physics. The degree to which this affects ICP test results or not depends upon whether they are reporting in w/w units or w/v units, and if w/v units, then whether or not this is accounted for in the method used by the laboratory in question. Ideally, ICP labs would be reporting results in w/w units, or w/v units adjusted to NTP -- normal temperature and pressure, which would mean 20C.

I think that running high salinity in order to keep Mg levels up would unnecessarily stress animals. Just keep Mg levels high, and salinity at or a little below S=35.

 

[infinite0180]

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

 

[Cory]

To the degree that temperature affects the density of tank water and/or test kit reagents, then of course. We are measuring these liquids by volume, and as the density of the liquids changes, so does the mass contained within that volume.

There is nothing magical about ICP that makes it immune to the basic laws of physics. The degree to which this affects ICP test results or not depends upon whether they are reporting in w/w units or w/v units, and if w/v units, then whether or not this is accounted for in the method used by the laboratory in question. Ideally, ICP labs would be reporting results in w/w units, or w/v units adjusted to NTP -- normal temperature and pressure, which would mean 20C.

I think that running high salinity in order to keep Mg levels up would unnecessarily stress animals. Just keep Mg levels high, and salinity at or a little below S=35.

I agree. Im more into keeping the big 4 parameters elevated or rather in the middle of the max and min to accomadate for innacuracies and allow drift.

My thoughts came up because i have three devices to measure salinity/sg. First my swing arm hydrometer read 1.0245 and my handheld refractometer was reading 1.025. I just got the milwalkee digital refractometer and it read 1.026.

Soo i was a little frustrated at which to trust but i suspect its 1.025. And as you can see my readoning to keep it at 1.027 to allow room for error. What do you think?

 

[Cory]

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

Its a good article thanks. I was unaware of calibrating a refractometer at 20c. Not sure how to do that though lol. My house is at 25 all day. Id especially love to try and evaporate and weigh my saltwater to determine the salinity without temperature problems.

 

[Cory]

Curious, could i just boil 1000 grams of tank water and get a good estimate of the salinity? Like it should weigh 35 grams?

 

[Randy Holmes-Farley Verified Community Expert]

More energy as in calories? Wouldnt a reef fish or coral have been adapted to "saltiness" and thus not be affected by these minimal differences in salinity but where we see things suffer most is when these "electrolytes" like cal mag and potassium get low. And since sodium and chloride make up most of this energy this shouldnt be a concern no? What im trying to say is spending less energy seems to say there is a flaw in their biology and they haven't sufficiently adapted to their salty environment and thus lower salinity is somehow bettter than higher. These "electrolytes" are what we maintain for proper health because they decline. We wouldnt think the same for the air we breathe no? Like its better to live in 60% nitrogen atmosphere instead of 80% because we spend less energy. Sorry just trying to understand

This article discusses some of the ways organisms try to adapt to salinity changes

http://jgp.rupress.org/content/145/5/381

 

[Randy Holmes-Farley Verified Community Expert]

Curious, could i just boil 1000 grams of tank water and get a good estimate of the salinity? Like it should weigh 35 grams?

Not the best way, but it can mostly work. As I mentioned in the other thread, some solids vaporize before all water is removed.

 

[madweazl]

Wait, did Randy just write saltiness? I'm getting a screen capture...