Salinity versus Temperature

Tommy Gun · 09-28-2006, 06:00 PM

Hello everyone!

Quick question, does anyone know or have some sort of idea if salinity will rise or fall as the water temperature rises? I am wondering because I normally will make RO water without heating it first. Then I add the salt while I am heating the tank. I wanted to better understand what happens so that I know to add too little salt when the water is colder or more salt when it is cold. In reality, its not a huge problem for me, but I thought it would just be nice to know! Thanks

WhoDey · 09-28-2006, 08:15 PM

The salinity of water doesn't change with temp changes, just it's saturation point. At least not enough for you to notice. The salt will disolve quicker in warmer water and can actually hold more salt the warmer water gets. You could have 100 degree water and 35 degree water and try to mix as much salt as you could in both, the result would be that you would end up with more salt in the 100 degree water(even when you bring them to the same temps). Another fact about water that doesn't really effect you because you aren't using thousands of gallons of water in your tank is that water expands as it gets colder. Think about a beer you put in the freezer when you are drunk, and then forget about it and it explodes. THis is because the water in the beer expanded. All the molecules start to attach to each other as you reach the freezing point causing an expansion of whatever liquid is cooling off. I know this is probably more info than you wanted, but you didn't have to read it all!

-N

Tommy Gun · 09-28-2006, 08:19 PM

Thanks Who!

I usually consider myself a pretty educated guy and the reason I asked this question is because it made no sense to me that my salinity would raise or lower as my tank's temp changed (in the event that it would, which it won't). I understand better now the principle and yes, I have been the dumb drunk who forgot to take the six pack out of the freezer before!

richardsantink · 09-28-2006, 10:21 PM

Quote:

Originally Posted by WhoDey

The salinity of water doesn't change with temp changes, just it's saturation point. At least not enough for you to notice. The salt will disolve quicker in warmer water and can actually hold more salt the warmer water gets. You could have 100 degree water and 35 degree water and try to mix as much salt as you could in both, the result would be that you would end up with more salt in the 100 degree water(even when you bring them to the same temps). Another fact about water that doesn't really effect you because you aren't using thousands of gallons of water in your tank is that water expands as it gets colder. Think about a beer you put in the freezer when you are drunk, and then forget about it and it explodes. THis is because the water in the beer expanded. All the molecules start to attach to each other as you reach the freezing point causing an expansion of whatever liquid is cooling off. I know this is probably more info than you wanted, but you didn't have to read it all!

-N

Just remember, the *salinity* may not change but the specific gravity *does*. You should be able to Google to find charts that show the different SG's at different temperatures.

RAS

ahill3780 · 09-29-2006, 12:22 PM

Hey guys,

First off, salinity does change with temperature.

Here is some info for you guys to help clear up the confusion:

Salinity and Specific Gravity are essentially the same thing. They are both the measurement of salt level in a given solution.

Salinity is measured in Parts Per Thousand (ppt) whereas Specific Gravity is measured in Parts Per Million (ppm), but they both measure salt content.

In example = Salinity of 32 ppt is equivalent to a Specific Gravity of 1.022 ppm. (differs slightly at different temperatures)

Since salinity is the measurement of salt content in a smaller volume of water (ppt vs ppm) temperature changes are easier to gauge when reading in ppt (salinity).

Here is a readout of what you might expect to see at different temperature ranges without any change to salt content: (referenced from Pet-Warehouse)

Based on a Specific Gravity of 1.022

69.8 F = 29.8 ppt
71.6 F = 30.2 ppt
73.4 F = 30.5 ppt
75.2 F = 30.9 ppt
77.0 F = 31.2 ppt
78.8 F = 31.6 ppt

Looking at the chart above we can deduce that for every 1.8 degree of difference in the temperature we get a change in salinity of between 0.3 and 0.4 ppt in salt content.

HTH,
Aaron

WhoDey · 09-29-2006, 02:14 PM

Hello all,

I guess I need to check the dictionary before I open my mouth again! I thought salinity was the measurement of salt relitive to volume of water. But actually it's actually the measurement of the density or "specific gravity" of the water. I agree that will change as pointed out by the last two posts. That does bring up a question I have though. Is it the salinity or the temperature of the water that we are most worried about? I understand that you should be at the correct salinity at the correct temp, but what happens to fish in the ocean when the water temp drops 10-20 degrees on them? Either they swim into a cold pocket or even a seasonal change in the water temp. may have an impact on the fish's health. So how do this apply to the home aquarium? Say you mix your salt in when the temp is 10 degrees of as mentioned in the first post. Is the really going to effect a fish in a negaive way? I don't think the difference in salinity is that big of a deal because it happens all the time in the wild. I think the ideal range that everyone is shooting for is nothing more than an educated guess on what the oceans salinity is. Help me out here Aaron, where did this range come from?? The Carribean, Atlantic, pacific?? I bet they are all different. Just food for thought. This is all really a big question, so anyone please feel free to put in your opinion. I'm guessing that this range must be the "ideal" for fish to live in after lots of studdies in the lab, but I don't know. Maybe they actually took various samples from the ocean and came up with an average... sounds crazy.

-Nate

ahill3780 · 09-29-2006, 03:15 PM

Hey Nate,

The world's oceans are so vast that nothing changes in them rapidly.

Quote:

Is it the salinity or the temperature of the water that we are most worried about?

Both are equally important, but what is more important when considering both is the stability of the chosen range. It doesn't matter as much which temperature or salinity you keep the tank at so much as how well it stays at that range. Rapid changes kill, while slower changes are adaptable for the livestock. When corals and invertebrates are included then the changes must be very slow to avoid harm.

Quote:

what happens to fish in the ocean when the water temp drops 10-20 degrees on them?

This does not happen, and if it did then 90% of the life would die.

Changes in ocean temperature and salinity are very slow to take hold and are slow enough that the inhabitants can either adjust, or migrate to warmer climates.

Quote:

Say you mix your salt in when the temp is 10 degrees of as mentioned in the first post. Is the really going to effect a fish in a negaive way?

Fish, not really - Corals and Inverts, maybe, depending on how much water is exchanged and how big the difference between the temps of the tank and the makeup water. A 50% water change is going to have a bigger impact than a 15% change would. You have to remember that the water is going to dilute itself in with the tank water so it isn't as if you were taking the fish from one environment and throwing them suddenly into the other.

Quote:

where did this range come from?? The Carribean, Atlantic, pacific??

Biological research throughout the past 150 years has shed light on many different ocean organisms. Each and every one of these organisms have different ranges that they favor. They are not always found in these ranges in the wild, they have just been found to do better in these ranges when tested in controlled experiments.

Natural sea water does differ in different regions, but usually these changes are due to the differences in regional temperature. There are special cases where the enviroment is mostly landlocked and freshwater rivers feed into them, this would cause the salinity to be lower in some regions but overall the oceans parameters are rock steady and very no more than a degree or two from one location to another.

I think Randy Holmes-Farley can explain this much better than I could. Here is a link to one of his articles published in Reef Keeping Magazine:

Reef Aquarium Water Parameters by Randy Holmes-Farley - Reefkeeping.com

HTH,
Aaron