Why Does Salt Water Evaporate Faster Than Fresh Water?

[[e-mail]]

I know this thread is old, but I was curious of this same question. I have two fish tanks, one 20 gallon fresh water and one 40 gallon salt water. I add about 2 gallons of fresh water to my saltwater tank every few days. I do not have to add freshwater to my freshwater tank but once a month when I clean it. The tanks are pretty much side by side in the same room so they endure the same temperature daily. Why would so much water evaporate from the salt water tanks. Anywho, any feedback is greatly appreciated.

Regards,
Chris

[Frank]

Post by ***@hotmail.com
I know this thread is old, but I was curious of this same question. I have two fish tanks, one 20 gallon fresh water and one 40 gallon salt water. I add about 2 gallons of fresh water to my saltwater tank every few days. I do not have to add freshwater to my freshwater tank but once a month when I clean it. The tanks are pretty much side by side in the same room so they endure the same temperature daily. Why would so much water evaporate from the salt water tanks. Anywho, any feedback is greatly appreciated.
Regards,
Chris

https://www.reference.com/science/salt-water-evaporate-faster-fresh-water-623992f1334fa845

[r***@gmail.com]

This is true I have had freshwater tanks for more than 30 years. And I just switched over to saltwater and I cannot believe how many gallons it loses in a week. I am spending so much money on salt. I appreciate your comment because it's so true. After 30 years of doing fishtanks I can tell you that this is a fact. All I can really think of is that there's more water movement. Which maybe causes more of evaporation. Considering I am moving more than 3000 gallons a hour in a 90 gallon fish tank. But I still think it's strange. Take it easy

[dlzc]

Post by ***@hotmail.com
I know this thread is old, but I was curious of this
same question. I have two fish tanks, one 20 gallon
fresh water and one 40 gallon salt water. I add
about 2 gallons of fresh water to my saltwater tank
every few days. I do not have to add freshwater to
my freshwater tank but once a month when I clean it.
The tanks are pretty much side by side in the same
room so they endure the same temperature daily. Why
would so much water evaporate from the salt water
tanks. Anywho, any feedback is greatly appreciated.

The answer is here:
https://www.thespruce.com/the-importance-of-proper-aeration-2921460

Arguments that water does not preferentially evaporate from a free saltwater surface vs. a freshwater surface are moot. Henry's law states that more gas being bubbled through the water, as required to get / keep the oxygen levels up to required levels, will necessarily carry off more water vapor.

If you aerate your freshwater aquaria like you do your salt water aquaria, you will have to add even more water to them. And probably wear those fish out trying to withstand the higher induced currents... ;-) just kidding.

David A. Smith

[Lenny Jacobs]

Post by dlzc

Post by ***@hotmail.com
I know this thread is old, but I was curious of this
same question. I have two fish tanks, one 20 gallon
fresh water and one 40 gallon salt water. I add
about 2 gallons of fresh water to my saltwater tank
every few days. I do not have to add freshwater to
my freshwater tank but once a month when I clean it.
The tanks are pretty much side by side in the same
room so they endure the same temperature daily. Why
would so much water evaporate from the salt water
tanks. Anywho, any feedback is greatly appreciated.

https://www.thespruce.com/the-importance-of-proper-aeration-2921460
Arguments that water does not preferentially evaporate from a free saltwater surface vs. a freshwater surface are moot. Henry's law states that more gas being bubbled through the water, as required to get / keep the oxygen levels up to required levels, will necessarily carry off more water vapor.
If you aerate your freshwater aquaria like you do your salt water aquaria, you will have to add even more water to them. And probably wear those fish out trying to withstand the higher induced currents... ;-) just kidding.
David A. Smith

When reading people's claims that salty tank needs more water, I always
assume both salty and fresh tanks are aerated (and to the same extent.)
Not true? If one is aerated, the other isn't, of course, there is no
comparison.

[dlzc]

Dear Lenny Jacobs:

On Wednesday, September 27, 2017 at 6:36:18 PM UTC-7, Lenny Jacobs wrote:
...

Post by Lenny Jacobs
When reading people's claims that salty tank needs more
water, I always assume both salty and fresh tanks are
aerated (and to the same extent.) Not true? If one is
aerated, the other isn't, of course, there is no
comparison.

Please read the link provided. To get the oxygen levels up in salt water takes more air. And since salt water is denser, the air is at a higher pressure (Henry's again). It is a function of the mass flow rate of air, being different in the two types of tanks.

I don't assume people are lying, I assume they tell the truth.

David A. Smith

[Peter Jason]

Post by ***@hotmail.com
I know this thread is old, but I was curious of this same question.

I have two fish tanks, one 20 gallon fresh water and one 40 gallon
salt water. I add about 2 gallons of fresh water to my saltwater tank
every few days. I do not have to add freshwater to my freshwater tank
but once a month when I clean it. The tanks are pretty much side by
side in the same room so they endure the same temperature daily. Why
would so much water evaporate from the salt water tanks. Anywho, any
feedback is greatly appreciated.

Post by ***@hotmail.com
Regards,
Chris

If salt is xtallizing on the sides of the salt tank, this may act as a
wick, so speeding evaporation.

[Alaia]

Why does salt water evaporate faster than fresh water? My science is a bit
sketchy. From what I understand (I'm an English major, forgive me), salt water
evaporates faster because the atomic charge of salt water is different from
that of fresh water. Salt, I think, also absorbs water? I've heard that
rubbing salt in an open wound causes the wound to heal faster because salt
absorbs blood, for example. Salt somehow changes the molecular balance of
water. Am I on the right track? Can someone recommend a book I can find in a
library that answers the question? Sorry if the question is too basic.
Thanks!
--
Cindy Smith
Spawn of a Jewish Carpenter
GO AGAINST THE FLOW! \\ _\\\_ _///_ //

IXOYE=('> <`)= _<< A Real Live Catholic in Georgia

Delay not your conversion to the LORD,
Put it not off from day to day
Ecclesiasticus/Ben Sira 5:8
Read Catholic.Bible by pointing your news client to vega.vec.net
Read Catholic.Literature by pointing your news client to vega.vec.net

When NaCl dissolves in water, Na+ and Cl- ions form ion-dipole interaction with water.

As water is evaporated from salt water, less water is available to form ion-dipole interaction with Na+ and Cl- ions. This results more ionic bonds between Na+ and Cl- to be formed, releasing heat energy to further evaporate more water in salt water. Hope this helps.

Alaia
A-level Chemistry teacher in Singapore

[Libor 'Poutnik' Stříž]

Post by Alaia

Why does salt water evaporate faster than fresh water? My science is a bit
sketchy. From what I understand (I'm an English major, forgive me), salt water
evaporates faster because the atomic charge of salt water is different from
that of fresh water. Salt, I think, also absorbs water? I've heard that
rubbing salt in an open wound causes the wound to heal faster because salt
absorbs blood, for example. Salt somehow changes the molecular balance of
water. Am I on the right track? Can someone recommend a book I can find in a
library that answers the question? Sorry if the question is too basic.

When NaCl dissolves in water, Na+ and Cl- ions form ion-dipole interaction with water.
As water is evaporated from salt water, less water is available to form ion-dipole interaction with Na+ and Cl- ions. This results more ionic bonds between Na+ and Cl- to be formed, releasing heat energy to further evaporate more water in salt water. Hope this helps.

If water evaporated faster from salt water,
then at the same temperature,
vapour tension over salt water would be higher than over pure water.

But opposite is true.

With higher concentration of sodium chloride,
the water vapour tension decreases
to about 75 % for the saturated salt solution.
That means air closed over the saturated salt solution
has relative humidity near 75 %.

IF you put saltwater and freshwater into a closed container,
freshwater will evaporate and saltwater will absorb the vapour.

[Oumati Asami]

Post by Alaia

Why does salt water evaporate faster than fresh water? My science is a bit
sketchy. From what I understand (I'm an English major, forgive me), salt water
evaporates faster because the atomic charge of salt water is different from
that of fresh water. Salt, I think, also absorbs water? I've heard that
rubbing salt in an open wound causes the wound to heal faster because salt
absorbs blood, for example. Salt somehow changes the molecular balance of
water. Am I on the right track? Can someone recommend a book I can find in a
library that answers the question? Sorry if the question is too basic.
Thanks!
--
Cindy Smith
Spawn of a Jewish Carpenter
GO AGAINST THE FLOW! \\ _\\\_ _///_ //

IXOYE=('> <`)= _<< A Real Live Catholic in Georgia

Delay not your conversion to the LORD,
Put it not off from day to day
Ecclesiasticus/Ben Sira 5:8
Read Catholic.Bible by pointing your news client to vega.vec.net
Read Catholic.Literature by pointing your news client to vega.vec.net

When NaCl dissolves in water, Na+ and Cl- ions form ion-dipole interaction with water.
As water is evaporated from salt water, less water is available to form ion-dipole interaction with Na+ and Cl- ions. This results more ionic bonds between Na+ and Cl- to be formed, releasing heat energy to further evaporate more water in salt water. Hope this helps.
Alaia
A-level Chemistry teacher in Singapore

In water, sodium and chloride ions are solvated. I don't think ionic
bond between sodium and chloride ions is possible in water unless salt
starts to crystallize out of water. But then, that's ionic bond in
sodium chloride crystal, not in water.

Also, the title is against Raoult's law.

[CRAIG MASON]

Post by Oumati Asami

Post by Alaia

Why does salt water evaporate faster than fresh water? My science is a bit
sketchy. From what I understand (I'm an English major, forgive me), salt water
evaporates faster because the atomic charge of salt water is different from
that of fresh water. Salt, I think, also absorbs water? I've heard that
rubbing salt in an open wound causes the wound to heal faster because salt
absorbs blood, for example. Salt somehow changes the molecular balance of
water. Am I on the right track? Can someone recommend a book I can find in a
library that answers the question? Sorry if the question is too basic.
Thanks!
--
Cindy Smith
Spawn of a Jewish Carpenter
GO AGAINST THE FLOW! \\ _\\\_ _///_ //

IXOYE=('> <`)= _<< A Real Live Catholic in Georgia

Delay not your conversion to the LORD,
Put it not off from day to day
Ecclesiasticus/Ben Sira 5:8
Read Catholic.Bible by pointing your news client to vega.vec.net
Read Catholic.Literature by pointing your news client to vega.vec.net

When NaCl dissolves in water, Na+ and Cl- ions form ion-dipole interaction with water.
As water is evaporated from salt water, less water is available to form ion-dipole interaction with Na+ and Cl- ions. This results more ionic bonds between Na+ and Cl- to be formed, releasing heat energy to further evaporate more water in salt water. Hope this helps.
Alaia
A-level Chemistry teacher in Singapore

In water, sodium and chloride ions are solvated. I don't think ionic
bond between sodium and chloride ions is possible in water unless salt
starts to crystallize out of water. But then, that's ionic bond in
sodium chloride crystal, not in water.
Also, the title is against Raoult's law.

Yada, yada, yada...I have an idea, conduct the experiment and find out which one evaporates faster...I could tell you, but then that would defeat the process of learning and finding out for yourself...spoiler alert, a lot of the responses on here are WRONG!