Refractometer

[clown-lover]

I should have added that you don't use the coke bottle. When I made my solution, I used a graduated cylinder (precise to 1 mL( and a mass scale (accuarate to .05 g). That way I knew it would be accurate.

Sure now you tell me.. LOL

I have also made standards for nitrate, phosphate, and alkalinity. That is how I know my test kits are off .

Have you posted that? That would be a GREAT article to have lying around here!

Again Thanks for the help.

 

[leoslizards]

Which refractometer did you get? Link? I'm looking to buy one soon.

 

[ddols]

I can assure you that if done with accurate equipment, this standard is better than anything on the market. There is a Pinpoint salinity calibration solution, but for whatever reason, it has become too variable. Back when they were more precise, these calibration solutions would match perfectly with the homemade standard. I'll trust my multiple solutions far more than anything I can get anywhere else. BTW, I have also made standards for nitrate, phosphate, and alkalinity. That is how I know my test kits are off .

Hmmm interesting. I just got one of those cheaper RHS-10ATC refractometers off ebay. Calibrating it with RO/DI water it pretty much gave the same reading as my instant ocean hydrometer (withing a couple thousandths SG). Using the pinpoint fluid it was WAY off.

Calibrating the refractometer with the pinpoint fluid to 35 PPT, I mixed up some water to 35 PPT. My hydrometer now reads 38 PPT. A old Coralife hydrometer I got used and never trusted reads 32 PPT. This just cast doubts on my assumptions. Going back to the RO/DI the refractometer reads below the 0 mark. If it had marks below 1.000 it would be between .002-.003 SG below 1.000 or 3 PPT. About the same as the instant ocean hydrometer is off by. This has really been making me doubt the fluid more then anything. And the fact that the American Marine website says nothing about the fluid being useful for calibrating refractometers makes me think this use is nothing more then an urban myth at best.

I'm going to have to try the home made standard I guess, but ideally I'd like to compare readings to some sort of salinity monitor that is known to be accurate. I wish I had more faith in any of my close LFS to have accurate measuring equipment.