Refractometer recommendations

[malawinovice]

Is one better than another?

DR fosters
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=9957&Nty=1&Ntx=mode+matchallpartial&Ntk=All&pc=1&N=0&Ntt=refractometer&Np=1

or
Sybon
http://www.thatpetplace.com/pet/prod/199289/product.web

Both are ATC

any feedback, both on sale.
thanks

[chrissreef]

i dunno, just ordered mine from ebay for 21 - edit, once calibrated imo they're probably all the same

[JaredWaites]

The ones on Ebay are great, I've seen a few in our local area and they are accurate once calibrated.

[malawinovice]

ebay, do you have the resellers name?
or auction example?

[liquidglass]

I got mine on ebay a while back also but do not remember the vendor.
They are pretty much all the same once calibrated.

[Jefe12234]

Make sure you calibrate with a 35ppt salinity standard, not freshwater. When calibrated with freshwater (RO/DI or distilled), they tend to be off by a few ppt at NSW salinity. (Mine was off by 3ppt.) You can buy Pinpoint 53.0mS calibration fluid from many places and it's only a few dollars for a big bottle.

[schneijt]

Just out of curiosity, does anyone know what the 53.0mS solution should read on a refractometer at room temperature (approx. 70 degrees)? I remember searching for that answer a while ago on Google, and hearing mixed results. IIRC, temperature and other factors may influence the reading. But when calibrating with the Pinpoint solution, what does everyone here use for the S.G. value of the testing solution?

Thanks,
Joe

[Jefe12234]

The calibration solution has a salinity of 35ppt and the refractometer should have a salinity scale to calibrate at that point. I believe the corresponding specific gravity at 70 degrees is 1.0264. Temperature can influence this, but with an ATC (automatic temperature correcting) refractometer it shouldn't be an issue.

And here's more than you ever wanted to know about refractometers.

http://www.reefkeeping.com/issues/2006-12/rhf/index.php#11

[cthetoy]

<a href=showthread.php?s=&postid=11778745#post11778745 target=_blank>Originally posted</a> by Jefe12234
Make sure you calibrate with a 35ppt salinity standard, not freshwater. When calibrated with freshwater (RO/DI or distilled), they tend to be off by a few ppt at NSW salinity. (Mine was off by 3ppt.) You can buy Pinpoint 53.0mS calibration fluid from many places and it's only a few dollars for a big bottle.

If its still under warranty I would return your refractometer. What you have is a slope miscalibration. A working refractometer will calibrate equally on both the low and high end.

Your refractometer is ok now for measuring NSW but wont be accurate if you decide to treat your fish with hypo treatment.

[Jefe12234]

I think slope miscalibrations are pretty common with hobbiest grade refractometers. There are threads on this forum full of people reporting the same problem. Maybe some work better than others, but I wouldn't trust any refractometer without checking it against a salinity standard. Good point on the hypo treatment, though.

[schneijt]

<a href=showthread.php?s=&postid=11779160#post11779160 target=_blank>Originally posted</a> by Jefe12234
The calibration solution has a salinity of 35ppt and the refractometer should have a salinity scale to calibrate at that point. I believe the corresponding specific gravity at 70 degrees is 1.0264. Temperature can influence this, but with an ATC (automatic temperature correcting) refractometer it shouldn't be an issue.

And here's more than you ever wanted to know about refractometers.

http://www.reefkeeping.com/issues/2006-12/rhf/index.php#11

Thanks!

-Joe