Specific Gravity vs Density Question

[Randy Holmes-Farley Verified Community Expert]

It does seem that the conductivity of the probe is sensitive to temp as temp is required to calibrate it.

Yes, for sure temp is needed to get the proper conductivity, which must always be corrected to the equivalent conductivity at 25 deg C. All conductivity measurements make this correction.

But my question is the density conversion. Is it supposed to be the density at the temperature measured, or the density at, say, a fixed 20 deg C or some such thing.

 

[Randy Holmes-Farley Verified Community Expert]

So if I use conductivity, I should be targeting roughly 51 for an sg of 1.025...

Why do you want to target that level? It's fine, but is only 33.7 ppt/PSU.

 

[arking_mark]

Why do you want to target that level? It's fine, but is only 33.7 ppt/PSU.

Good question. I always thought it was good to have a buffer up or down in case of errors. So recommended salinity was always 1.023 - 1.026 sg. Has this changed? Is 35ppt the sweet spot with room up and down?

 

[Randy Holmes-Farley Verified Community Expert]

Good question. I always thought it was good to have a buffer up or down in case of errors. So recommended salinity was always 1.023 - 1.026 sg. Has this changed? Is 35ppt the sweet spot with room up and down?

Salinity has a wide range of OK, but I've never thought targeting anything but 35 ppt had much justification, except perhaps an LFS trying to save money.

 

[arking_mark]

Salinity has a wide range of OK, but I've never thought targeting anything but 35 ppt had much justification, except perhaps an LFS trying to save money.

I'm convinced. So set point will be 53ms/cm.

Thanks again @Randy Holmes-Farley !!

 

[arking_mark]

Yes, for sure temp is needed to get the proper conductivity, which must always be corrected to the equivalent conductivity at 25 deg C. All conductivity measurements make this correction.

But my question is the density conversion. Is it supposed to be the density at the temperature measured, or the density at, say, a fixed 20 deg C or some such thing.

If it's using a fixed temp, that would, in my opinion, be a large miss/bug with monitoring and controlling your tank.

 

[taricha]

Here's a great thread on what it actually takes to measure density well enough to calculate salinity to a digit past the "35" as in 35.X ppt
https://www.reef2reef.com/threads/salinity-determination-by-density.238209/

(it kinda convinced me that density is nuts and s.g. is the path of sanity.)