Measuring Salinity & result changing every few seconds....

[mythesis]

Greetings! I'm new to the hobby and trying to understand why my salinity tests are so sensitive.

I also was encouraged to buy the Milwaukee Digital Refractometer by my LFS.

I have the 1.000 and 1.025 calibration fluids that came with the Milwaukee and use them frequently.

However, when I read my tank water.... the salinity on the MIlwaukee changes frequently.

For instance today I :

• Calibrated (1.000) fluid
• Wiped clean, filled well with RODI water, wiped clean again
• Filled well with tank water
• Read: 1.024
• Waited 30-40 s; Read: 1.025
• Waited: Read 1.026
• Waited: Read 1.025
• Waited: Read 1.027
• Waited: Read 1.026

The ATC visual one held steady at 1.025 throughout.

This happens frequently, and especially when I'm mixing the water --- so it makes it very hard to determine as a new hobbyist if I'm mixing up the right amount of salt or not.

Tips/ideas?

 

[Randy Holmes-Farley]

The Milwaukee has a claimed uncertainty of +/- 0.002 in sg, so those results are reasonable and you should just average them, IMO.

 

[mythesis]

The Milwaukee has a claimed uncertainty of +/- 0.002 in sg, so those results are reasonable and you should just average them, IMO.

Gotcha, thanks.

I was led to believe that Salinity is like #1 to keep constant in the tank for the safety of the fish. Should I be measuring another way?

 

[Randy Holmes-Farley]

Gotcha, thanks.

I was led to believe that Salinity is like #1 to keep constant in the tank for the safety of the fish. Should I be measuring another way?

No. Salinity will be adequately constant if you keep the tank properly topped off to replace evaporation, and exact salinity numbers are not really that important. Some effects may lead to slowly rising salinity (such as using a 2/3 part system for alk and calcium), but your device is fine to deal with that.

 

[Randy Holmes-Farley]

FWIW, be sure to wait a bit to take a reading:

"Note: If the temperature of the sample differs significantly from the temperature of the instrument, wait approximately 1 minute to allow thermal equilibration."

 

[mythesis]

ok, thanks, I'll be more careful to allow the temp to stabilize before reading.

Appreciate the quick responses, as a new guy it's very overwhelming to understand what's important vs. not and how to stay on top of the important things.

 

[Flyangler33]

I battled this same thing I started my tank in march, I use the hannah tester, tank was reading 1.026 I took a sample to my LFS and had them test just for shiggles before i got my first clownfish. They said it was reading 1.030. So adjusted my tank and water accordingly. Come to find out I took a sample to a different LFS and my tester was in align with theirs and now my salinity was way off because I listened to the LFS. Even being new if you follow the instructions and calibrate trust your equipment.

Now i calibrate my tester before I make each batch of water and before water changes and everything has been golden.

 

[KrisReef]

I don't have this meter, but I would probably use the 1.025 calibration solution to calibrate the meter as that is closer to the number you want to measure.

A mentioned first, I don't have the instrument so I would follow the directions for calibration and remember that the idea is to keep the salinity stable when you do water changes so that it doesn't swing about during any water change.

I would also mention that fish and coral can tolerate some movement in salinity, and in generaly fish are much less sensitive to these changes than the inverts we want to keep, if we have them.

An auto top off system to replace evaporation is a great tool for reef and fish tanks to avoid swings, ime. GL!

 

[trainbob]

I have this instrument and have found it works better if you place your palm over the prism and bring it up to the temperature of your tank water and then measure it

 

[mythesis]

I have this instrument and have found it works better if you place your palm over the prism and bring it up to the temperature of your tank water and then measure it

You mean just let it sit for a minute with the water in the well before measuring?

It seems to align better when the handheld one when I do that.

 

[trainbob]

Before I take a measurement I place my palm over the prism and bring it up to the temperature of the tank water and then pour the water into the prism and take the measurement