Refractometer problem

[leafyseadragon]

I bought a refractometer from Marine Depot a few years ago. It's worked perfectly---until this week. Now it seems to register only 1.021 for both of my tanks and fresh seawater. When I put pure water in, it does register 1.000 though.

After looking at the instructions again, it says to clean the prism with a soft, damp cloth or you'll get inaccurate results and damage the prism's coating. I've been using a damp paper towel to clean the instrument.

Given my results, have I damaged the prism's coating with the paper towel? It looks fine to me, unless all the coating is gone. There are no moving parts here, right?

And more importantly, do I need to buy a new one?

 

[Gti_Leo]

i doubt you damaged it, do you see any scratches on the lense?

it may just be old, over time they do need servicing, but you can get realitivly cheap ones on ebay for $25 i just got mine on friday and it works well so it might just be worth getting a new one

 

[leafyseadragon]

Nope, there are no scratches on the lens that I can see.

 

[Kurt_Nelson]

Recalibrate it using 53mS calibration fluid for salinity probes. That fluid will calibrate to 35ppt or between 1.026 and 1.027. Then you should be good to go. Calibrating at 1.000 doesn't really do you any good, unless you're testing 1.000 water.