lobsterotomy
I'd frag it.
If you have access to a spec, what wavelength would you run it at to determine discolouration of your reef's water?
Measuring water discolouration with a spec?
- Thread starter lobsterotomy
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In my Advanced Marine Aquarium Techniques book, I describe a method for using a Hach spectrophotometer to measure true and apparent color in the aquariums:
"For Hach brand spectrophotometers, method number 8025 is used to determine the true and/or apparent color of any water sample with results given in platinum-cobalt (PtCO) units in a range of 0 to 500.
Apparent color is a combination of dissolved coloring agents such as organic wastes, certain inorganic compounds, and tannins (sometimes collectively called "gelbstoff') combined with any suspended matter. This is the "real" measurement, in that this is what one's eye perceives when viewing a given aquatic exhibit. True color is derived from a sample that has been pre-filtered or centrifuged to remove the suspended particulate matter. This measurement gives the user an idea of the potential benefit, which might be gained with carbon filtration or partial water changes desired to remove or dilute the gelbstoff concentration. The relation of these two values is important to understand; a high apparent color combined with a lower true color reading indicates that the mechanical filter of a given system is not sufficient to achieve proper particulate filtration of the water volume. A high true color, nearly equal to the apparent color indicates that mechanical filtration is sufficient, but that excessive gelbstoff is present, and should be removed by chemical filtration or water exchange. A true color reading greater than the apparent color reading indicates some error in the test procedure; for example not insuring that the outside surface of the sample cell, is clean, or not pre-rinsing the filter paper to remove any loose fibers. "
I don't know how this applies to other brands of specs. If you can get access to the Hach DR series spec manual, you should be able to determine the nm you need to use. There is no reagent needed for this test.
Jay Hemdal
"For Hach brand spectrophotometers, method number 8025 is used to determine the true and/or apparent color of any water sample with results given in platinum-cobalt (PtCO) units in a range of 0 to 500.
Apparent color is a combination of dissolved coloring agents such as organic wastes, certain inorganic compounds, and tannins (sometimes collectively called "gelbstoff') combined with any suspended matter. This is the "real" measurement, in that this is what one's eye perceives when viewing a given aquatic exhibit. True color is derived from a sample that has been pre-filtered or centrifuged to remove the suspended particulate matter. This measurement gives the user an idea of the potential benefit, which might be gained with carbon filtration or partial water changes desired to remove or dilute the gelbstoff concentration. The relation of these two values is important to understand; a high apparent color combined with a lower true color reading indicates that the mechanical filter of a given system is not sufficient to achieve proper particulate filtration of the water volume. A high true color, nearly equal to the apparent color indicates that mechanical filtration is sufficient, but that excessive gelbstoff is present, and should be removed by chemical filtration or water exchange. A true color reading greater than the apparent color reading indicates some error in the test procedure; for example not insuring that the outside surface of the sample cell, is clean, or not pre-rinsing the filter paper to remove any loose fibers. "
I don't know how this applies to other brands of specs. If you can get access to the Hach DR series spec manual, you should be able to determine the nm you need to use. There is no reagent needed for this test.
Jay Hemdal
OwenInAZ
New member
If your spec has a setting where you can measure a range of wavelengths (say 200 nm to 800 nm) you can find the peak absorbance in your sample and go from there. Cells will absorb in the ~600 nm range (but are probably too scarce to register), proteins around 280 nm. These are probably what discolor the water (aside from other DOC).
But assuming you have a spec that can scan a range, I'd just blank with some freshly made water and go from there. HTH
But assuming you have a spec that can scan a range, I'd just blank with some freshly made water and go from there. HTH
I doubt you'd be able to reproducibly detect any absorbance from normal reef tank water with a normal spectrophotometer except in the UV and perhaps in the near UV range. The path length is just too short, and without carefully matched glass or quartz cells, it is too hard to detect the small absorbance with any confidence. I've tried it on my system. 
You could measure reflectance just below the surface of the water and then at the bottom of the tank. The difference would be a approximation of the relative reflectance of the water. But you would need to use a diffuse reflectance target and black out the sides of your tank and coralscaping.
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