Refractometer help

[spencka]

I have a Refractometer, with no instructions. Can someone explain how to read the right hand side of the meter? It has PPT which I would guess means Parts per Thousands - but it also has a % symbol.
Can anyone help explain?
Thanks!

 

[bang guy]

ppt is the (hobby) measurement for Salinity. Natural Seawater around tropical reefs is typically 35 - 37ppt, you should keep yours in that range.

 

[spencka]

Thanks Bang Guy - mine is 35

 

[ron thomas]

So, when my refractometer arrived, I made sure a drop of distilled water read zero ppt. Then I wanted a second calibration point so I carefully weighed 3.5 grams of Instant Ocean mix and dissolved it in 100 ml of distilled water. What do you think it read? What do you think I used as my next calibration point?

 

[bang guy]

I've seen a recipie for a good calibration fluid. You need a bit more volumn unless you really do have instruments that are that precise. The recipie was from Dr. Randy Holmes-Farley.
1/4 cup + 1 teaspoon of table salt dissolved with a 2 liter coke bottle filled completely to the brim. Mix the ingredients in a seperate, larger container.
This solution should read 35ppt on your refractometer.

 

[ron thomas]

I've got access to a good lab balance so it's not a problem. In my earlier post, when I used IO as the calibration mix, I forgot about all of the components that didn't contribute to salinity. So, when it measured at only about 32 ppt I was upset until I realized that and used table salt instead.

 

[bang guy]

Interesting to know, thanks!