Reef Chemistry Puzzle #11

[Miami Reef]

Imagine this: Your tank lights are currently in their “actinic” or dusk period. You enjoy the aquarium during the mornings at, let’s say, 460nm (blue) because of the coral’s fluorescence.

You calibrate your refractometer with that aquarium light with a standard solution of 35ppt or a refractive index of 1.3394 (seawater salinity). The aquarium reads 35ppt.

Later that afternoon, your power and aquarium light go out. The entire house is pitch black, and the only light you have is an incandescent light, which, for this purpose, shines about 650nm (orange).

You calibrated the refractometer earlier this morning with the blue light. You recheck the aquarium salinity to ensure everything is still OK.

Because of the difference in light from the calibration time from the morning (blue light) to checking it now (orange light), the current salinity reading has:



A) Fallen slightly lower from the morning.

B) Risen slightly higher from the morning.

C) Fallen drastically from the morning.

D) Skyrocketed up from the morning.

E) Not changed at all from the morning.

Bonus: What salinity, in ppt, do you think the aquarium reads during the power outage?

Have fun with this one! :)


Previous Reef Chemistry Puzzle:

https://www.reef2reef.com/threads/reef-chemistry-puzzle-10.1022400/

 

[Miami Reef]

Added additional info for clarity. :)

 

[reefluvrr]

is this related to red field ratio...ooops I meant to say red shift vs blue shift of light?

 

[EeyoreIsMySpiritAnimal]

The reading using the candlelight will be lower than the one using actinic light.

 

[Miami Reef]

The reading using the candlelight will be lower than the one using actinic light.

Do you have an estimate as to what the newer salinity would read?

 

[Randy Holmes-Farley Verified Community Expert]

Very interesting learning question!

I had to look a couple of things up, and the answer was surprising to me. :)

 

[Miami Reef]

Bump! Where are my Grasshopper Chemists at?

 

[EeyoreIsMySpiritAnimal]

Do you have an estimate as to what the newer salinity would read?

Did you accidentally test your freshwater tank? ;)

 

[Randy Holmes-Farley Verified Community Expert]

Did you accidentally test your freshwater tank? ;)

lol good answer

 

[Miami Reef]

Answer will be posted tomorrow.

 

[Miami Reef]

@EeyoreIsMySpiritAnimal was correct

Because of the difference in light from the calibration time from the morning (blue light) to checking it now (orange light), the current salinity reading has:


A) Fallen slightly lower from the morning.

B) Risen slightly higher from the morning.

C) Fallen drastically from the morning.

D) Skyrocketed up from the morning.

E) Not changed at all from the morning.

The answer was ”C.” If you calibrated your device with a refractive index of about 1.339 (35ppt) with blue light, and the aquarium reads about 35ppt, by simply changing the light to a higher wavelength (orange) to read the measurement, that would make the 35ppt salinity water read like freshwater about (1ppt).

It is paramount to use the same lighting to take refractometer readings as the light in which you used to calibrate it with.

Here’s a graph. We used the blue line for the example in the question:

This post goes a little bit more in depth: https://www.reef2reef.com/threads/refractometers-and-the-color-of-light-used-important.174560/

 

[Randy Holmes-Farley Verified Community Expert]

Good question. While I knew there was an effect, I never realized it could be so big!