refractometer or pinpoint salinity monitor

[AFH]

Esmithiii P.S

"The optics in your refractometer will be damaged if the unit is submerged or if fluids come into contact with any part other than the sample plate"

This is not the case with Acquamarine refractometers.

my salinity meter was not submerged in water, water got on the face plate seeped in. My refractometer manual says if water enters the body call qualified service technician because meter will become foggy. You neglected to mention how often you must calibrate your salinity meter. I can check my refatometer calibration with distilled water. How many sources besided CAL tec have you found for the calibration solution. Also Refractometers are not affected by electrical interference. I no longer use Pinpoint salinity meter. I do however use a Neptune pro controller. In my experience with Pinpoint salinity meter you must wait longer than 30 second of the reading to stabilize. Refractometers do not need batteries.

 

[Big R]

"The only issue I have had from the pinpoint monitor was that after a year of use, it started acting strangely."

That is not much of a testimonial.

I have used both and now only use/recommend the refractometer.

R

 

[Anonymous]

Any decent conductivity meter will be more precise. A properly-functioning, well-calibrated one will, in addition, be more accurate. This is the rub. For most people, including me, the refractometer is more useful because (a) it is really simple to calibrate (with distilled water at a know temperature and a set screw), (b) it is precise enough -- my salinity fluctuations due to evaporation before and after manual, slothful topoffs is well beyond the error of these things, and (c) it is extremely easy to use, cheaper (my lab grade VWR one was $120, but I have seen the exact same thing for $70) unless you want to buy a really high-end one which is total overkill.

But Randy is correct. Also a conductivity meter will measure ions directly (via current they carry) whereas if you have a lot of organic goo, this can change the refractive index of your water and give you a false reading. I think this is probably a minor problem in practice but one that you need to be aware of.

 

[randy holmes-farley]

Leonard:

To answer your specific question about how different ions impact conductivity, here's an article that I wrote. Click on Biochemistry of Aquaria, and then scroll down to the article on conductivity:
http://www.reefs.org/library/aquarium_frontiers/index.html

Many of the same arguments apply to refractometers and even hydrometers: the primary ions will control the measurement, and minor to trace elements will have no measurable effect.

I agree that some labs use both refractometers and conductivity probes. We (a pharmaceutical company) only use the latter. In both cases, they cost more than hobby equipment.

The 2001 VWR lab supply catalog lists refractometers from $152 to $10,269. The cheapest is intended for salt water measurements, and claims an accuracy of 1 ppt. Fine for hobby applications, but not especially accurate. Several hundred dollar refractometers have similar accuracy. For comparison, the big boy has an accuracy 5 times better (0.2 ppt).

Conductivity? Again, VWR lists conductivity meter/probe combinations from $62 to $1532. The lowest doesn't cover the seawater range, with the cheapest doing so being $246. The salinity accuracy ranges from 0.1 to 0.2 ppt for all of these.

[ September 26, 2001: Message edited by: Randy Holmes-Farley ]

 

[Len]

Randy, thanks for the article.

 

[esmithiii]

Big R:

I am in no way endorsing any product; I am just stating the facts. The conductivity meter is easier to use, hands down. I am not convinced that the pinpoint monitor is the unit I would buy again. The question was which one is more accurate, and the conductivity is more accurate (as well as more precise) and it is easier to use.

Lobster: You have a hydrometer, not a conductivity monitor.

E