Refractometer problems

[srpntmage]

I have been testing my new tanks water with a refractometer. The water was from my friend who works at an aquarium building and maintenance company. He told me it is tested constantly and used in every tank they maintain. It read 1.025 exactly. RODI water read 0.0.

I went by the LFS the other day to pick up some calibrating fluid for my refractometer, just to make sure it was absolutely dialed in. I was given pH 7.01 buffer solution in a small factory sealed pouch, and told that it should read zero on the meter. My meter reads this fluid as 1.010. Any idea what is going on? I know calibration fluid is usually a saltwater mix, not a pH solution. Did the store screw up, or is my refractometer that far off.

 

[NJAB]

I would pick up a bottle of distilled water, as distilled water is 0 and test it with that you will then be able to compare if your meter is off or its the pH solution.

 

[Scott07]

I've been through similar refractometer issues recently myself. It can make your head hurt right lol?? My humble suggestion would be to pick up some actual refractometer calibration fluid which will calibrate the instrument at or near your target test zone. So... 35ppt for most folks. RO/DI or Distilled may or may not get you pretty darn close... but with a new bottle of solution... you can be pretty close to certain that you are calibrated correctly.

 

[billsreef]

The store screwed up. Can't use pH buffer for calibrating a refractometer

 

[reepher315]

I ordered a bottle of calibration fluid for like 5 bucks online. Mine was waaaayyy off.

 

[disc1]

The store screwed up. Can't use pH buffer for calibrating a refractometer

This +1. I don't know what the RI of that solution is but it definitely isn't pure water.

 

[disc1]

If you've got a good scale you can DIY it. 36.5g of table salt in 963.5g of water (feel free to scale that down) Will match seawater in refractive index and can calibrate your refrac.

 

[srpntmage]

I just bought some real calibration fluid. I'll check it out tonight. I think the LFS I went to was smoking crack.

 

[acabgd]

I found the best is Tropic Marin big hydrometer which reads up to 0.0001, then calibrate the refractometer based on this reading.

 

[chris.scang]

If you've got a good scale you can DIY it. 36.5g of table salt in 963.5g of water (feel free to scale that down) Will match seawater in refractive index and can calibrate your refrac.

Would this DIY make 35ppt seawater?

 

[billsreef]

Would this DIY make 35ppt seawater?

It doesn't make 35ppt seawater. What it does is make a brine (NaCl) solution with a refractive index that matches the refractive index of 35ppt seawater.

 

[reepher315]

I wish I knew that a week ago lol. Thats what I get for not looking more into it.

 

[chris.scang]

It doesn't make 35ppt seawater. What it does is make a brine (NaCl) solution with a refractive index that matches the refractive index of 35ppt seawater.

Thanks for the reply. I wanted to make some to test my refractometer but I was unsure of what level it should read.

Chris

 

[disc1]

Thanks for the reply. I wanted to make some to test my refractometer but I was unsure of what level it should read.

Chris

On your refractometer it should read 35ppt. The extra 1.5ppt of NaCl is there to make up for the difference in refractive index between seawater and pure saltwater brine.