First, refracts are NOT more accurate that hydrometers. We have proved this many times. It is user error not the instrument or the user not understanding them.
instant ocean hydrometer and have been using it for about 5 months.
How do you treat it or take care of it ?
IO Swing Arm Hydrometer:
1. After each use it needs to be rinsed well in RO/DI water, the SAME for a refract.
2. You need to check the arm for bubbles to make sure there are not any as bubbles cause the arm to rise more. All you really need to do its put it on a flat surface and tap it lightly.
3. They should be stored wet and not dried off and put in a zip-lock back in a drawer.
4. Once a month soak in pH 4 cal solution over night or vinegar and rinse well in warm RO/DOI water.
5. One MUST also remember that a swing arm is a mechanical device !!
They can be MOE accurate than a refract due to the larger divisions. When one uses a swing -arm, tests the water, just pours it out and just lets it sit someplace wetted with seawater and not rinsed with RO/DI water, the water evaporates and leaves salt deposits on the arm. This adds weight to the arm, weighing it down more, making it more inaccurate and giving false low readings. The SAME with a refract, as the salt deposits on the lens and cover-slip change the RI ( Refractive Index). A refract too needs to have both the lens and cover slip rinsed in RO/DI and the paper towel dried.
Refracts:
1. Most are cheap Chinese crap, such as any of those cheap ones and 99 % of them are just that.
2. These are NOT seawater refracts but table salt refracts that are factory set to table salt NaCl, for Saline solution's. The RI of table salt and seawater are NOT the same. On a expensive hand-held Lab grade, when calibrated in RO/DI water, they will always read 1.5 pp to low. That means to achieve NSW Salinity, when calibrate in RO/DI water, the refract needs to read, 36.5 ppt and not 35 ppt, where 35 ppt ( 1.264 sg) is the NSW std.
3. To make a cheap Chinese refract more accurate and only for a narrow salinity range, i.e, 32- 38 ppt or there abouts, you need to calibrate it in a seawater std, such as
Pin-Point 53 mS std solution. And NOT some other Conductivity std that says 53 mS/ The Pin-Point is actually a mock seawater solution.
4. Failure to not follow 2 & 3 and just calibration it in RO/DI water the refract can be off from 0 -4 ppt, due to the cheap and poor quality control of the glass optics.
5. There is only one company in this hobby that makes REAL seawater refracts, that CAN be calibrated in RO/DI and that is Vee Gee. They are sold by Jim Grassinger at The Filter Guys, under that name. They are also sold by Foster & Smith under their name Vital-Sin. They are the exact same unit. These units are twice the price as the cheap Chinese ones ` $100. Their window view is a very sharp, clear, distinct, clean and easy to read window, unlike the cheap Chinese ones.
The Filter Guys
http://thefilterguys.biz/refractometers.htm
Foster & Smith
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+4690+12132&pcatid=12132
These are examples of cheap Chinese crap
1.)
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+4690+9957&pcatid=9957
2.)
http://www.marinedepot.com/Captive_...meters-Captive_Purity-CP2111-FITEOPRF-vi.html
ANYBODY that says 1 & 2, or any others like them, are made for seawater are full of BS and I DARE them to come here for a debate on the issue.
The only other true/real seawater hand-held refract is the one I helped ATACO with a few years back, a Lab grade at the tune of ~ $250. The so called real seawater refract by Deltec is NOT a real seawater refract, despite the efforts of them to make one on the data I gave them.
In short, that many find swing-arms a pain, which they can be, IMHO most are better off with refract. A cheap Chinese one is fine as long as it is calibrated in Pin-Point 53 mS or some other KNOWN seawater std. that can be used on a refract. However, in the long run, a Vee-Gee is a better deal.
