Refractometer....

So I have a refractometer and wanted to know if anyone has this problem with theirs. For some reason, I'm always calibrating this thing. At first I thought it was temperature, but the thing says it has temperature correction. For example, this morning it was reading lower than the night before, so I used the cal solution and readjusted. Then this afternoon, I went to measure and it was way high, so I re-cal'd it again. The end result of my tank salinity is always the same, so I'm pretty sure it's accurate after it's cal'd. Sometimes it'll be fine for couple days, then out again. And I say that I it's off because it's like WAY off. Like it'll read 1.010, then when I re-measure later that day, it'll be like 1.015 and vice-versa. I make sure to handle it carefully everytime cause I know this thing is sensative. I'm so worried that it's not reading correctly that I'm now basically calibrating it every time I take a reading, but I don't think this is the norm, or is it? Is my refractometer jacked or what?

 

Try reading some distilled water with it. If you do it 3 times in a row, and it's not reading 0 every time, then, yeah--it's jacked.

I've never heard of such a thing though. Refractometers work on refraction of light thru a prism, so they're not capable of swings. . . unless the chart inside the unit is loose??

If the chart is loose, then in your case, distilled water would have a different reading every time.

 

Can I use RO water instead of DI? With my calibration fluid, I can repeat the reading more than 3x's in a row.

 

well di is deionized its not the same as distilled. but yea you should be able to use RO water assuming your filters arent old.

the key is to use water you know has nothing in it just good old h20

 

If you can get repeatability with your calibration fluid, then there's nothing wrong with your instrument.

It's like when you're lost in the woods with your compass. Novices will trust their instinct. True outdoorsmen will trust their compass.

A compass can't lie. Neither can a refractometer. Trust your refractometer, grashoppa.

Your salinity is jumping around for a reason. Find the reason, and find your problem.

You're not replacing evaporated water with salt water, are you? You're not doing water changes with fresh water, right?

 

The QT tank is in hyposalinity mode. But the thing is I haven't replaced the water when I took those readings, and it's got these rinky dink flourescents plus it's in a cool part of my place, so it's not evaporating water, and I wouldn't think that quick. It's just weird I get different readings within the same day. I guess I'll just have to keep re-cal everytime I use it, no big deal. Thanks for all the insight guys!

 

Ok, so I think I figured it out. Even though this thing says temp correction, I think temp is still a factor. This morning, I felt the refractometer and it was pretty cold to the touch. When I measured salinity with the cal solution, it read about .006 higher. I then waited for a little bit holding it to try to warm it up a bit and didn't adjust anything. About 5min later with it warmer to the touch, I remeasured w/cal solution and it hit right on at the cal solution value. At least I know now how to get this thing to work ;D.

 

hope you got it figured out...

one other thought, make sure you rinse it off or clean it after each use. the test water will evaporate and leave salt on the tool skewing the next reading if you don't...