August 03, 2020, 11:35:00 AM
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Topic: water monitoring - saltwater reef tank  (Read 185 times)

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Offline jeremyrutman

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water monitoring - saltwater reef tank
« on: July 02, 2020, 07:29:29 AM »
I have a reef fish tank (saltwater) I'm setting up and see that there's a number of water parameters people monitor . I'd prefer having an online monitor rather than hand-checking with reagent bottles, so I found I can monitor ammonia in gas and alkalinity in water with  cheap meters; for nitrate/nitrite it seems I'd need a spectrometer.
Are there cheap spectrometers (like 200$ or less) to be had that would let me check nitrate (which has a 200nm-220nm absorption, apparently)?
Alternatively is there another approach to this?
 
Things to monitor in fish tank water:
ammonia 
alkalinity   
nirate
nitrite
Phosphate
calcium
magnesium
ph

Offline Corribus

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Re: water monitoring - saltwater reef tank
« Reply #1 on: July 02, 2020, 12:51:08 PM »
Even a basic model (single wavelength) Visible spectrometer will probably run you a few thousand dollars if you buy it new. UV capability will add a lot of cost because you need an additional light source. You may be able to find an old, used model on the cheap but 200$ or less may be a stiff ask.

Keep in mind that the analysis isn't as simple as it sounds and you won't be able to ditch the reagents completely. If you want a concentration, you'll have to maintain a series of concentration standards. You'll also need to do some method development to ensure there are no interferences.

If you have no background in chemistry, this may be a challenging analysis to get going.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline jeremyrutman

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Re: water monitoring - saltwater reef tank
« Reply #2 on: July 03, 2020, 10:54:17 AM »
From this manual here I got some pointers  - it seems I only need a few wavelengths e.g. 220nm and 340nm which I can detect with diodes like this .  The light source can also apparently be a cheap xenon lamp , avoiding the 50$ for a deuterium lamp. I was thinking I cold increase athe pathlength for higher sensitivity but the extinction is already around 99% at 10cm pathlength for the levels I am anticipating (5-10ppm) .
So for nitrate and nitrate it looks like I have a decent plan. I imagine the elements (Mg, Ca)  and phosphate will be tougher but apparently those are less crucial than ammonia and nitrate.
nitrate absorption curves

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