Mixed reef salinity

[fishytime]

.024 for me as well

[chewie]

The best way to keep track of the salt levels is using ppt (35) not specific gravity (1.024 ect). It is due to how salanity changes due to water temp -where as salanity (ppt) does not. I could try to go into the details myself but I just copied and pasted a very good explanation for you. Thank you broomer5 (saltwaterfish.com)


The whole salinity vs specific gravity issue is not too tough to figure out. It all depends on the instruments used to do the measurements, what temperature they are calibrated for and which engineering unit you prefer to go by.

Salinity is expressed in parts per thousand ( ppt ).
It's just a measurement of the weight of the salt/minerals compared to the weight of the pure water.
Normal seawater is typically 35 ppt in most areas of a reef.

It could be 35 grams of salt per 1000 grams of water.
It could be 35 pounds of salt per 1000 pounds of water.
It could be 35 tons of salt per 1000 tons of water.

You could even use your own body weight as an engineering unit.
I weigh about 175 pounds.
I could easily say that the salinity of seawater is 35 broomer5's of salt per thousand boomer5's of water.
The weight ratio of salt (solids ) to water ( liquid ) is 35 TO 1000

Using ppt as the units then - the salinity would be considered to be 35 ppt at ANY temperature.

SPECIFIC GRAVITY on the other hand is not a weight to weight comparison. It is a weight to volume comparison.
When we talk weight to volume ~ we are talking DENSITY.
Density is just how much something weighs compared to how much space it takes up.

Picture a little clear acrylic cubic box that measures 1cm x 1cm x 1cm on the inside.
Fill it with pure water.
It now contains 1 cc ( cubic centimeter ) of water.
This little clear box of water contains exactly 1 milliliter of water.
1 cc = 1 ml

Now if you could weigh just the water in this little box ~ How much would the water alone weigh ?

The answer is IT DEPENDS.

The actual weight of this volume of pure water will depend on the temperature and the atmospheric pressure.

The metric standard for weight is grams.
It just so happens that this little clear box of water we have, if it's temperature was 4 degrees C ( 39.2 F ) and it was at sea level where the atmospheric pressure is 1 atmosphere ( 14.7 psi ) then the 1 cc of water ( 1 ml ) would weigh in at a whopping 1 gram.

In other words ~ 1 cc of water is 1 ml of water and weighs 1 gram. Were talking PURE WATER here.

This is how people came up with the term "Specific Gravity"
The DENSITY of water ~ how much it weighs ~ for a given VOLUME is referred to as the SPECIFIC GRAVITY.

In our pure water example above - the specific gravity would be 1.000

1.000 gram of pure water in a 1.000 cubic centimeter container.

Now the tricky part.

Water ( in a LIQUID state ) expands and contracts with temperature changes.
The warmer it is - it expands.
The cooler it is - it contracts.
When water expands or contracts - it either takes up more volume or less volume. But the amount of salt in the sample does not change. Only the volume of the water changes.
The ppt stays the same.

So ......... if we're using specific gravity as our measurement - we need to always look at the temperature of the saltwater too.
Specific gravity is a measurement of the WEIGHT of salt to the VOLUME.
Specific gravity is a measurement of the saltwater's DENSITY as compared to DENSITY of pure water - for the same volume of each.

There are a ton of charts on the internet, and in most any decent marine aquarium book. I can send you a chart if you want a good one. Be careful though - there are some contradicting charts floating around out there.

We'll use 3 different temperatures as examples, and the chart goes something like this.

At 60 degrees F
35 ppt = 1.026 S.G.

At 70 degrees F
35 ppt = 1.025 S.G.

At 80 degrees F
35 ppt = 1.023 S.G.

As you can see - the salinity is the same for each example.
It's still 35 ppt

But as the temperature goes up - the specific gravity goes down.

This is simply because the water expands at a higher temperature - and the density must therefore change as well.

Back to our little clear acrylic box of saltwater now.
The box is full of saltwater with a salinity of 35 ppt.

At 60 degrees F - the saltwater in this little box now weighs 1.026 grams.

At 70 degrees F - the box of same saltwater weighs 1.025 grams.

At 80 degrees F - the box of same saltwater weighs 1.023 grams.

The temperature of the saltwater MUST BE considered when using specific gravity as the measurement.

Okay you say - How does all of this crap mean anything to me and my marine tanks ???

You need to see what TEMPERATURE your hydrometer is CALIBRATED for.

Most refractometers or hydrometers are calibrated for liquids at a given temperature. The swing arm units like FasTests - I don't know what they are calibrated for. I don't like using them for that reason - plus they don't seem to give me good results.
They're okay if that's all you have, I still have one too.

The refractometer I use is calibrated for 68 degrees F.

The floating glass hyrdometer is calibrated for 75 degrees F.

What you need to do then - is measure the mixed up aerated saltwater with your instrument and thermometer, and write both values down on paper.
Then refer to a specific gravity vs. temperature chart - find your temperture you just wrote down and see what the S.G. is for that given temperature.
From a good chart for the marine hobby - you will also be able to determine the PPT salinity as well.

I like to mix my IO and RO/DI water to a salinity of 35 ppt.

The actual specific gravity of that batch of saltwater may be differerent - depending on the actual temperature I read on my thermometer, the instrument I use for S.G./Density and the chart I'm looking at to do the conversion.

Normally - I heat the RO/DI water with a heater - get it up around 78 -80 F ( my tank temperature ) mix in IO saltmix at 1/2 cup per gallon freshwater - toss in a little more salt and let it run overnight.

Then the following day - when I plan to do the water change.
Get out my tools - take the two measurements, thermometer and refractometer - look at the chart and tweek it up or down with a little more salt or a little more fresh RO/DI.

After doing this several times - I get lazy too - repeat the same procedures as I have before, get it as close as I can - and move on from there.

It doesn't have to be exact. It does need to be very close though.

The reasons why density, ppt and specific gravity are what they are IS very exact in every respect ......... but for my tanks - getting it real close is fine for me.

If you made it this far reading - congratulations - you must be interested.
If you have anything to add to this thread - please do so.
We're always interested in trying to figure all this stuff out - and any other views would be appreciated

Plus - if it looks like my chart is not correct - please let me know.
As I said - there are several different charts out there - and I may have the wrong one too

[cwatkins]

I try to keep it at 1.025.

[StirCrazy]

Originally Posted by chewie

The best way to keep track of the salt levels is using ppt (35) not specific gravity (1.024 ect).

at the design referance temp (60 degrees F)
34.5ppt is actualy 1.026 not 1.024.
1.024 would be 31.9.

but this is confused more because people don't list the referance temp they are using for therte tables so you don't know. then I found two tables that said 80 degrees but were the values for 70 degrees

the problem is that you are not measuring salinity you are measuring the SG then coralaiting it to lines some one wrote beside the SG ones which will only corasponde at 60 degrees.

Originally Posted by chewie

What you need to do then - is measure the mixed up aerated saltwater with your instrument and thermometer, and write both values down on paper.
Then refer to a specific gravity vs. temperature chart - find your temperture you just wrote down and see what the S.G. is for that given temperature.

well you could buy and ATC one for 10 or 15 bucks more but you will have to use the SG scale as the salinity scale will be wrong.

Steve

[paddyob]

I keep mine at 1.024. I like it here as a little evaporation only raises it a couple points.... about 1.026.

[paddyob]

Originally Posted by cathyg_99

just wondering what you keep your salinity at... im slowly trying to raise mine to around 1.025-1.026 but i was told by someone that "THATS STUPID"

Did you ask why they thought so?

[Maverick00]

Originally Posted by Money pit

Mines at 1.025, Because its a thick line on my refractometer. I'm too blind to see the smaller lines.

lol....


1.025@80F

[Jewel]

I guess i've always had it a tad high at 1.027, but i never thought that the fish would stress as much as the coral would.

[cathyg_99]

Originally Posted by paddyob

Did you ask why they thought so?

they said i was because its to stress full for the fish... isnt a normal reef 1.026?? lol

[mechano]

I keep mine at 1.026. I have had no problems or issues.
This is a silly question tho. If my SG is 1.026, wouldn't the other elements and minerals in my saltwater be a little higher(like calcium and magnesium)than say if I used a 1.024 SG? That is why I use a little higher on the SG scale. JMO. But if I were running a larger system then say a 40-50g+ I think I would probably run my system a tad lower on the scale as with larger tanks you dose more so it would seem more realistic to run your SW at 1.024 SG(not due to cost either). In a smaller system, your WC water pretty much takes care of your calcium/mag/ replenishing of minerals.
Hard to say in all honesty. 1.024-1.026 seems to be the general rule for sure tho.