Question about refractometer

Hello all. I was doing a Mag test and my refractomiter is out of calibration. I am saposed to use distiled water to calibrate it. Can I use RO water?

 

RO/DI can be used in its place.

 

I though most places say it's preferable to use a saline calibration solution.

 

The instructions from the marine depot one i have say distilled water.

 

well use what ever the instructions tells you, yes RO/DI is probably purer then distilled.

 

Just want to get a true reading. I did not have any distilled water. Thanks for the advise guys.

 

Unless your refractometer is a true marine salt water one, (most are not), then calibration with distilled or RO/DI will result in incorrect but close readings at normal salt tank salinity.
For some basics of measuring with refractometers, see this article: Refractometers and Salinity Measurement by Randy Holmes-Farley - Reefkeeping.com