How does temp affect salinity reading ?

[Lesley]

Hi. Did my first real ocean water change. Been using Red Sea coral pro first 12 months. Went to beach collected 150liters and took home to heat. Collection Water temp 18.5 sal 1.032. After heating. Temp 25.5. Salinity 1.029. Each if these readings were done with a calibrated refractometer. Why/ how does temp affect the salinity. ?? All other reading were spot on. Little light on cal but dosed to correct that.

 

[redfishbluefish]

With increasing temperature, salinity decreases....and conversely, with decreasing temperature, salinity increases. You ask why.....density!

 

[Lesley]

Thank you !

 

[SloppyJ]

Open and shut.

 

[ReefMadScientist]

Good read. Mixed water in my 115 degree garage. Took it in for the night to get to room temps. Next day my water went from 1.025 to 1.029. Re-mixed the water and now it is super cloudy. Looks like I will wait till tomorrow to do my water change.

Hate AZ.

 

[redfishbluefish]

You'd be better off bringing the water "in" before you add the salt. Solubility is better at cooler temperatures. You most likely have carbonate ppt going on at those higher temperatures.


My daughter lives in Scottsdale....bloody hot out there!!!

 

[ReefMadScientist]

You'd be better off bringing the water "in" before you add the salt. Solubility is better at cooler temperatures. You most likely have carbonate ppt going on at those higher temperatures.


My daughter lives in Scottsdale....bloody hot out there!!!

Yeah the heat is a pain. Its been getting worse lately.

I think I may dump this batch and make a fresh one for tomorrow. The cloudiness makes me not want to attempt this batch.

 

[Randy Holmes-Farley Verified Community Expert]

Unfortunately, I don't believe the above explanation explains to the OP situation, although I recognize I'm a year late to the party.

While density changes a lot with temp, specific gravity does not because you divide the density of the seawater by the density of pure fresh water. Both of them change similarly with temp.

IMO, the problem in the OP tests was likely a refractometer that didn't have perfect ATC (automatic temperature compensation).

 

[bdesign]

With increasing temperature, salinity decreases....and conversely, with decreasing temperature, salinity increases. You ask why.....density!

I hope it’s okay to resurrect such an old thread...?

Curious if you have an opinion/theory on this @Randy Holmes-Farley

If SG is inverse to temperature, what the heck is going on here?

Why is SG increasing?

- the peaks (and coinciding ORP dips) are daily around 4-5pm
- No recent water change
- no dosing
- ATO with ATK via RO/DI
- haven’t done manual test with refractometer YET

 

[AZMSGT]

I hope it’s okay to resurrect such an old thread...?

Curious if you have an opinion/theory on this @Randy Holmes-Farley

If SG is inverse to temperature, what the heck is going on here?

Why is SG increasing?

- the peaks (and coinciding ORP dips) are daily around 4-5pm
- No recent water change
- no dosing
- ATO with ATK via RO/DI
- haven’t done manual test with refractometer YET

I’m thinking electrical interference or stray voltage. Is anything timed to turn on at this time? Could be electrical cord running parallel to the sensor line.

 

[bdesign]

I’m thinking electrical interference or stray voltage. Is anything timed to turn on at this time? Could be electrical cord running parallel to the sensor line.

I’ll check the cords when I get to the office.

T5s are on at 10:00 and off at 16:30, so that doesn’t seem to have a correlation.

 

[Randy Holmes-Farley Verified Community Expert]

Assuming the real salinity is unchanged, the likely explanation relates to the apex using an incorrect or no temp correction to conductivity interpretation. It is a user settable feature that may be set wrong.

All controllers measure salinity by electrical conductivity if the water. That conductivity increases with temperature. Devices are supposed to make a correction back to a 25 deg C standard by knowing how the solution conductivity behaves with temp. If it makes that correction incorrectly or not at all, the reported salinity will rise and fall as temp rises and falls.

 

[bdesign]

Thanks @Randy Holmes-Farley
I’ll look into the interpretation setting...

Would that also account for the same UPtick in PH and DOWNtick in ORP at, essentially, the same times?

Salinity, Temp, and PH are all the same curve at the same times, and the ORP is the inverse curve and the same times.

 

[Randy Holmes-Farley Verified Community Expert]

No. Those cycle day to night due to photosynthesis.