Captive purity refractometer problem (35ppt=1.025sg)

[HippieSmell]

My Captive Purity refractometer that I got from marinedepot a couple years ago has a problem. I swear that 35 ppt reads 1.025 sg, when it should read 1.026 sg. Why it took me so long to realize this is beyond me, but does anyone else have a refractometer that does this? What do I do about it?

 

[Amphiprion]

35ppt should be around 1.0264, not 1.025. Did you check yours against the standard in the chemistry forum? It will help in determining which is the more accurate reading.

 

[HippieSmell]

I did check it against the standard about a week ago and it said 1.026 sg, just like it should. So, I guess the ppt scale is off. BUT, about a month ago a LFS said my salinity was way off, so that leads me to believe the sg scale is off on my refractometer (he had a different refractometer than I did). After that, I took a water sample to a different LFS (who had the SAME refractometer that I do) and it had the same reading mine had. SO, my refractometer is calibrated correctly for sg (as far as I can tell) but not ppt. This seems to be a problem with captive purity and was wondering if anyone else knew this. It is kind of important if you're using the ppt scale. Of course, I may be overlooking something and would like to compare with other people. I hope I explained everything well.

 

[travisurfer]

could it be the atc?

 

[HippieSmell]

If you have a captive purity refractometer, especially one bought from marinedepot a couple years ago, please check to see if 1.025 sg equals 35 ppt.

 

[HippieSmell]

<a href=showthread.php?s=&postid=7480376#post7480376 target=_blank>Originally posted</a> by travisurfer
could it be the atc?

I don't think so because the relative values between ppt and sg should be constant. They don't change relative to each other.

 

[HippieSmell]

No one has a captive purity refractometer?

 

[BeanAnimal]

I am not sure I understand your problem. Both scales are ground or painted onto the same piece of glass. How could one be off relative to the other unless it was painted wrong? So looking through the eyepiece, you should see that the 35ppt gradient is slightly offset (higher) from the 1.025 gradient line.

 

[HippieSmell]

That's exactly the problem, the engraving was done wrong so that 1.025 sg equals 35 ppt. I was just checking to see if anyone else had the same defect as me.

 

[BeanAnimal]

I have the marine depot bradn and it correct. I would contact marine depot and tell them.

I know nothing about "captive purity" but do know that dozens of companies market products to this hobby and many of those products are garbage. Don't always assume that listed specs or retail prices indicate the quality or suitability of a product.

Look at the "major brand" of pumps that poeple recently found with exposed metal components in them... the "brand" is nothing more than an office who buys junk from overseas, slaps a label on it and sells it as a "REEF SAFE" aquarium pump. I would suspect that some refractomoters are the same. Some guys calls some OEM and says "make one of these to look like this and work like that". They get it close enough and sell it as high end....

Shrug

 

[HippieSmell]

Yeah, I agree with you. It's hard to know if a product is of good quality sometimes. When I bought this refractometer it was the "recommended" one. Meh.

 

[HippieSmell]

^