Salinity - ppt vs S.G. (Need Help Knowing How To Properly Measure)

[JSkeleton]

So I got a Hanna Salinity Tester which by default is in ppt and the calibration packets are by ppt but can also measure by S.G..

Now, I heard that ppt is a more accurate measurement (correct me if I'm wrong) since it's based solely on salt, while S.G. factors in temperature (which gets confusing for me to be quite honest). So I was happy just going by ppt.

BUT...Every time I try to get info on best salinity for certain livestock, it's ALWAYS giving the salinity readings in S.G. and so I'm left scratching my head. So what should I do?

 

[blaxsun]

I personally like ppt myself. I aim for a level of somewhere between 35.0 and 35.5ppt (this is equivalent to roughly 1.0265).

 

[Jedi1199]

So I got a Hanna Salinity Tester which by default is in ppt and the calibration packets are by ppt but can also measure by S.G..

Now, I heard that ppt is a more accurate measurement (correct me if I'm wrong) since it's based solely on salt, while S.G. factors in temperature (which gets confusing for me to be quite honest). So I was happy just going by ppt.

BUT...Every time I try to get info on best salinity for certain livestock, it's ALWAYS giving the salinity readings in S.G. and so I'm left scratching my head. So what should I do?

What should you do? Don't worry about it. I mix my water to PPT. It doesn't matter if its plus or minus a point or 2, as long as you keep it the same all the time. What you don't want to do is change it drastically every time you do it. Say 40 one week and 30 the next.

 

[JSkeleton]

What should you do? Don't worry about it. I mix my water to PPT. It doesn't matter if its plus or minus a point or 2, as long as you keep it the same all the time. What you don't want to do is change it drastically every time you do it. Say 40 one week and 30 the next.

But if I'm for example looking up what salinity certain fish, inverts, and maybe one day corals (still undecided on corals) and trying to figure out what ppt to put my tank at, yet the measurements are all in SG, how do I figure out what that is in ppt if no where provides the info in ppt and only SG?

Also, regarding what you mentioned about 2 points difference, do you mean if I typically keep my tank at say 35ppt that if my new water during a water change is 33 or 37ppt that's okay and won't affect the fish or whatnot?

 

[JSkeleton]

I personally like ppt myself. I aim for a level of somewhere between 35.0 and 35.5ppt (this is equivalent to roughly 1.0265).

I do too, but how do we convert ppt and sg in real time? Like if SG is based on temperature as well as salinity, and if I'm looking up info on a certain livestock and it says say 1.023 salinity, how do I know what that is in ppt? For example I'm reading that Clownfish need 1.020 – 1.024 but if 35ppt is 1.0265 then I want to have my tank sitting more where in ppt?

 

[EricR]

It's not like the Hanna conductivity checker does anything differently when you switch from ppt to SG -- other than how it displays.

I leave mine in ppt mode just because it displays to 0.1 ppt while SG mode only displays to 0.001 SG,,, which is closer to a whole ppt point (if that makes sense).

Not like the measurement magically gets more accurate but the display is more granular reading, in my opinion.

EDIT -- by the way, for rough conversion, you can use a site like this:

Salinity Calculator

 

[Randy Holmes-Farley Verified Community Expert]

So I got a Hanna Salinity Tester which by default is in ppt and the calibration packets are by ppt but can also measure by S.G..

Now, I heard that ppt is a more accurate measurement (correct me if I'm wrong) since it's based solely on salt, while S.G. factors in temperature (which gets confusing for me to be quite honest). So I was happy just going by ppt.

BUT...Every time I try to get info on best salinity for certain livestock, it's ALWAYS giving the salinity readings in S.G. and so I'm left scratching my head. So what should I do?

Its like cm vs inches. It makes no difference which units you choose for a measurement.

 

[JSkeleton]

It's not like the Hanna conductivity checker does anything differently when you switch from ppt to SG -- other than how it displays.

I leave mine in ppt mode just because it displays to 0.1 ppt while SG mode only displays to 0.001 SG,,, which is closer to a whole ppt point (if that makes sense).

Not like the measurement magically gets more accurate but the display is more granular reading, in my opinion.

EDIT -- by the way, for rough conversion, you can use a site like this:

Salinity Calculator

So essentially, the Hanna is just doing it's own conversion then or? And so ppt displays more accurately I guess then?

Judging by that salinity calculator, Clownfish would be best kept at 28-33ppt salinity, does that sound right?

 

[JSkeleton]

Its like cm vs inches. It makes no difference which units you choose for a measurement.

Oh okay! But isn't SG based partly on temperature or? And are there accurate ways to convert (such as the calculator Eric linked), are conversions generally accurate?

As I asked him, for example, judging by a conversion Clownfish are best kept at 28-33ppt (if I was to use ppt that is)?

 

[Gtinnel]

Problem solved

Salinity Conversion Calculator

Aquarium calculator; Convert salinity between relative specific gravity (sg), parts-per-thousand (ppt), and units of conductivity (mS/cm).

www.hamzasreef.com

ETA- also you are going to ultimately pick a salinity that you want and try to keep it there. You won’t be trying to change the salinity of your tank based on a new addition. Most people just run their reef tanks around 35ppt

 

[Jedi1199]

But if I'm for example looking up what salinity certain fish, inverts, and maybe one day corals (still undecided on corals) and trying to figure out what ppt to put my tank at, yet the measurements are all in SG, how do I figure out what that is in ppt if no where provides the info in ppt and only SG?

Also, regarding what you mentioned about 2 points difference, do you mean if I typically keep my tank at say 35ppt that if my new water during a water change is 33 or 37ppt that's okay and won't affect the fish or whatnot?

First, unless you are getting fish from the dead sea, there is no reason why anything you get will need a salinity other than the standard 35 ppt. I have never had a single fish, coral or invert that had an issue with standard 35 ppt.

It is your responsibility to acclimate your new additions to your specific system.

Secondly, What I meant is that it doesn't matter if your tank runs at 34 ppt or 36 ppt... as long as you run it the same all the time. You want to mix your water to the same point on every batch. At least as close to it as you can. You have a very small tank, evaporation is going to cause swings in salinity. You will probably want an auto top-off on this tank. I would if it was mine.

 

[JSkeleton]

Problem solved

Salinity Conversion Calculator

Aquarium calculator; Convert salinity between relative specific gravity (sg), parts-per-thousand (ppt), and units of conductivity (mS/cm).

www.hamzasreef.com

ETA- also you are going to ultimately pick a salinity that you want and try to keep it there. You won’t be trying to change the salinity of your tank based on a new addition. Most people just run their reef tanks around 35ppt

Isn't 35 slightly on the high side though or no?

 

[Gtinnel]

Isn't 35 slightly on the high side though or no?

No 35 is a pretty common goal. There is at least one vendor I know of who runs his coral tanks even higher.

 

[EricR]

If you're new, it is confusing that a lot of online sites will list ideal salinity for fish/inverts at lower than 35 ppt. (Not sure why)

Like all have said, 35 ppt is the norm but some run 34 ppt (or slightly lower/higher),,, no big deal.

Best advice though (already stated) is, if you're going to change (especially from lower salinity to higher), do it SLOWLY until you get to where you want, then just maintain it.

 

[JSkeleton]

First, unless you are getting fish from the dead sea, there is no reason why anything you get will need a salinity other than the standard 35 ppt. I have never had a single fish, coral or invert that had an issue with standard 35 ppt.

It is your responsibility to acclimate your new additions to your specific system.

Secondly, What I meant is that it doesn't matter if your tank runs at 34 ppt or 36 ppt... as long as you run it the same all the time. You want to mix your water to the same point on every batch. At least as close to it as you can. You have a very small tank, evaporation is going to cause swings in salinity. You will probably want an auto top-off on this tank. I would if it was mine.

Well, I was considering a couple from the Dead Sea to be honest...haha jk. So 35 is sort of the happy middle or something? Currently my tank is at 33 but no fish yet (still cycling). I was under the assumption that 35 was going more towards the higher end but perhaps not!

And ah gotcha! I'm still trying to figure how to get as close to the same salinity every time and how to properly measure it haha. I have a 55 Gallon, so would I need to be topping it off that frequently?

 

[JSkeleton]

If you're new, it is confusing that a lot of online sites will list ideal salinity for fish/inverts at lower than 35 ppt. (Not sure why)

Like all have said, 35 ppt is the norm but some run 34 ppt (or slightly lower/higher),,, no big deal.

Best advice though (already stated) is, if you're going to change (especially from lower salinity to higher), do it SLOWLY until you get to where you want, then just maintain it.

Ah okay gotcha! Yeah, that's definitely where I'm getting quite confused haha I'm still cycling my tank, so now is the time for me to figure out what to try and get my salinity at and then maintain it there. I figured if I can get away with a bit on the lower end (33ppt or 34ppt if 33 is too low), then that also saves a bit of salt in the long run haha

 

[Gtinnel]

Well, I was considering a couple from the Dead Sea to be honest...haha jk. So 35 is sort of the happy middle or something? Currently my tank is at 33 but no fish yet (still cycling). I was under the assumption that 35 was going more towards the higher end but perhaps not!

And ah gotcha! I'm still trying to figure how to get as close to the same salinity every time and how to properly measure it haha. I have a 55 Gallon, so would I need to be topping it off that frequently?

The more often you replenish evaporated water the more stable your salinity will be. I would never run a tank without an ATO of some kind.
Fish can stand a huge range of salinity, but corals need to be closer to that 35 range.

 

[Randy Holmes-Farley Verified Community Expert]

So essentially, the Hanna is just doing it's own conversion then or? And so ppt displays more accurately I guess then?

Judging by that salinity calculator, Clownfish would be best kept at 28-33ppt salinity, does that sound right?

No, it is not doing it more accurately. It is just doing a mathematical calculation for each result from the actually measured conductivity.

It shows more precision as ppt, but with a claimed accuracy of +/- 1 ppt, the ability to read to 0.1 ppt is not of much value.

 

[EricR]

Re-stating some fundamentals for you, just to be safe:

1. Water evaporates but salt doesn't so you need to be topping off (at least daily) with "fresh" water, ideally RODI water.
2. Most use an auto top off (ATO) device to handle this automatically/smoothly -- definitely makes life easier but not a hard requirement.

*since you're topping off manually and already running lower salinity (I think), you might target a little lower than 35 ppt, like 34 ppt. (As water evaporates, salinity will increase slightly,,, then you bring it back down when you top off)

 

[Jedi1199]

Well, I was considering a couple from the Dead Sea to be honest...haha jk. So 35 is sort of the happy middle or something? Currently my tank is at 33 but no fish yet (still cycling). I was under the assumption that 35 was going more towards the higher end but perhaps not!

And ah gotcha! I'm still trying to figure how to get as close to the same salinity every time and how to properly measure it haha. I have a 55 Gallon, so would I need to be topping it off that frequently?

I'm sorry.. Mixing threads again. I was thinking you had a 13.5 evo.

I had a 55g for the last 18 months or so. I did top-offs by hand. Usually about 2 or 3 gallons every few days. With a tank that size, the evaporation is not going to cause much of a change in the overall parameters.

That said, it is still a good idea to have an ATO on your system. The less things change, the better.

Keep in mind that an ATO is worthless if you don't refill the reservoir. It's very easy to forget about it after you fill it up. Your brain says "I am good for a while" a few days later you realize it has run dry...