Salinity issues

OrthoVet05 · Mar 24, 2018

Hey guys I currently have a 75 gallon system and I have been having some major salinity issues during mixing and doing WC only. I’m definitely a nube to this but tend to see some discrepancies when I follow water mixing recipes in my Brutes

I have an ATO that adds RO/DI FW and my salinity generally is spot on 1.025 in my DT.

I did a recent ~10% WC and I mixed up some SW with the target salinity at 1.024 around 50 degrees F following the 1/2C reef crystals/gal. I currently do not have a heater for my water outside to match the temperature of my DT. I realize that is probably a large issue and proponent of this but still open to suggestions.

I added back in 10 gal of the 1.024 SW and with the Increased temperature of my tank (~78 F) I checked my salinity today and it was 1.030!!!!! Ahhh what gives.

My main question is..... at what salinity should I mix my SW to at 50 F to match 1.025 at 78 F? TIA!

Randy Holmes-Farley · Mar 24, 2018

How are you measuring salinity?

OrthoVet05 · Mar 24, 2018

Refractometer. I’ll take a clean dropper out and place one drop on it.

saltyfilmfolks · Mar 24, 2018

I found this to be an easier approach.
I mix all my salt by weight.
Let a 5g bucket of rodi come up to room temp. 77f.
Weight the salt mix even if the directions are in cups. , test, if you need to add, weight it. Then add.
If you need to water it down, use less next mix.

Instant ocean was 800 grams to five gallons of water. For .35.

No matter what the temp is when mixed, when it comes up to 77. It’s .35.

Red Sea salt has instructions to do this on the label. I think RCSP is 750 grams per 5g.

I’m working with fritz pro salt right now. (No instructions at all even in cups).
Still adjusting but it appears to be 760 grams per 5 gal of water.

Doing this I have never had to adjust once the weight amount has been confirmed.

I don’t know if it’s right or wrong but it seems to work every time.

Randy Holmes-Farley · Mar 24, 2018

OrthoVet05 said:
Refractometer. I’ll take a clean dropper out and place one drop on it.

How do you calibrate it, and is it an ATC (automatic temperature compensation) type?

50 deg F is a but below the normal range for ATC correction, I think.

With no correction at all, 35 ppt seawater at a temp of 50 deg F will mistakenly read a higher salinity than it really is.

So if you made that to normal "salinity' then added it to your tank and it warmed, the salinity value would be lower, not higher.

Thus I think the problem lies elsewhere than simple measuring cold and warming it up.

OrthoVet05 · Mar 24, 2018

Ha I guess I haven’t calibrated it before but would measure my fresh out RO/DI water and it would be at 1.000. Very crude I know.

OrthoVet05 · Mar 24, 2018

Randy Holmes-Farley said:
How do you calibrate it, and is it an ATC (automatic temperature compensation) type?

50 deg F is a but below the normal range for ATC correction, I think.

With no correction at all, 35 ppt seawater at a temp of 50 deg F will mistakenly read a higher salinity than it really is.

So if you made that to normal "salinity' then added it to your tank and it warmed, the salinity value would be lower, not higher.

Thus I think the problem lies elsewhere than simple measuring cold and warming it up.

Also it is an ATC.

Randy Holmes-Farley · Mar 24, 2018

Probably the 1.030 was just an error, or the tank specific gravity was 1.030 before the change.

I don't really see how anything you did can raise the salinity.

killr66tb · Mar 24, 2018

What about creep

OrthoVet05 · Mar 24, 2018

Hm well I definitely trust you but I did check it multiple times and now it’s down to 1.025 after a WC.

Randy Holmes-Farley · Mar 24, 2018

killr66tb said:
What about creep

Salt creep? That lowers salinity.

Salinity in the tank doesn't creep around on its own.

Randy Holmes-Farley · Mar 24, 2018

OrthoVet05 said:
Hm well I definitely trust you but I did check it multiple times and now it’s down to 1.025 after a WC.

Well, then certainly it was error, right?

If it was 1.030 in the tank and you did a 10 gallon water change using FRESH water with 75 gallons of tank water, it would only drop to 1.026.

OrthoVet05 · Mar 24, 2018

Randy Holmes-Farley said:
Well, then certainly it was error, right?

If it was 1.030 in the tank and you did a 10 gallon water change using FRESH water with 75 gallons of tank water, it would only drop to 1.026.

I would think that if the 1.030 were an error (from a true 1.025) then if I did 10 g FW change then it would be down to 1.021 right now.

Randy Holmes-Farley · Mar 24, 2018

OrthoVet05 said:
I would think that if the 1.030 were an error (from a true 1.025) then if I did 10 g FW change then it would be down to 1.021 right now.

I'm not suggesting you actually used fresh water. Is that even a possibility?

I'm showing how unlikely to was to be 1.030 before the change and 1.025 now, because even changing with pure fresh water would not drop it so low.

OrthoVet05 · Mar 24, 2018

Makes sense. I just want to verify that the salinity should only get lower based on the lower density if the temperature raises correct ?

Randy Holmes-Farley · Mar 24, 2018

OrthoVet05 said:
Makes sense. I just want to verify that the salinity should only get lower based on the lower density if the temperature raises correct ?

If it is a properly functioning ATC refractometer within the range of its ATC, then there is no effect on the reported measurement based on temperature.

If there was no ATC, the effect would be for the measured salinity or specific gravity to fall as the temp rises (note this is not a real effect on salinity, but in the refractive index of the seawater).

If the ATC is malfunctioning, or is outside its intended range, I'm not sure what exactly would result, but I can't see the effect explaining your result.

OrthoVet05 · Mar 24, 2018

Randy Holmes-Farley said:
If it is a properly functioning ATC refractometer within the range of its ATC, then there is no effect on the reported measurement based on temperature.

If there was no ATC, the effect would be for the measured salinity or specific gravity to fall as the temp rises (note this is not a real effect on salinity, but in the refractive index of the seawater).

If the ATC is malfunctioning, or is outside its intended range, I'm not sure what exactly would result, but I can't see the effect explaining your result.

Awesome. Thanks so much for the info Randy!

Ferrell · Mar 29, 2018

Did I catch the phrase I zeroed it with Rodi then measured? Should be using a calibration solution of .35 to calibrate. I think I read somewhere that zeroing it with rodi isn’t accurate. @Randy Holmes-Farley is that correct?

Randy Holmes-Farley · Mar 29, 2018

Ferrell said:
Did I catch the phrase I zeroed it with Rodi then measured? Should be using a calibration solution of .35 to calibrate. I think I read somewhere that zeroing it with rodi isn’t accurate. @Randy Holmes-Farley is that correct?

Depends on the device. Assuming you are technically able to do so, it is never wrong to calibrated to 35 ppt using a standard that matches the refractive index of 35 ppt seawater, and sometimes it is inherently inaccurate to use RO/DI