How to measure dissolved oxygen (DO) cheaply?
Domen wrote 05/29/2016 at 17:20 • 0 pointsI had and idea - to find a correlation of the DO level (0-10 ppm) with the pH change of water (CO2 has a soulability of 1700 ppm which makes the water acidic (Edited 31.5) and than use the correlation to measure the DO level from the pH level (pH meters are cheap, where as DO meters require expensive platinum probes which are expensive :(
But no correlation was to be found.
Also the winkler method looks long and expensive and automating such a test would take a lot of effort ...
This is the cheapest test I could find, it costs 15€ for 50 tests, which is 0.30€ for one test ... Not the cheapest thing in the long run idk. 
Any ideas?
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Maybe one could make his own clark electrodes? @Adam Vadala-Roth
https://publiclab.org/notes/JSummers/01-09-2014/potentiostat-notes-5-how-to-make-low-cost-electrodes
http://www.eidusa.com/Theory_DO.htm
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I'm going the probe method, but I will not be using Atlas Scientific products, I will be implementing all the electronics from scratch, I might buy a probe from them but its unlikely. I'm gonna be doing full water quality monitoring with both HydroPWNics and SunLeaf, so I'll be following your efforts to see if we can share more info on the subject, good luck!
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I could swear that I was able to find an DO probe for about 20 dollars on ebay or aliexpress a few months ago. I can not find them now. I may have confused the DO probe with the PH probe though.
This is the cheapest thing I found not. A probe for $25. You could order it since you are from the USA, however I can not provide any further information.
http://www.ebay.com/itm/SCI-Technologies-Dissolved-Oxygen-Sensor-R0036-in-Box-/322131821252
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Agreed with @odd arild olsen's comments re:optical DO, I think that's worth exploring if you have the time. I used to sell such probes (called 'optical DO', 'fluorescence quenching', 'blinky light sticks', etc) to the pharma industry and they had a number of advantages vs more traditional polarographic probes in terms of maintenance, durability, and lifetime cost of ownership. However, getting the chromophore coating on the end of the probe right is a real trick, along with the algorithms that adjust the calibration data as said chromophore inevitably ages. It's a seriously tough problem, especially if you want to do it accurately and in a less-than-favorable environment!
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Put a bunch of goldfish in there and measure the LD50
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Hahaha, made my day ! :'D
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Solubility of all gases decrease with temperature, so not specific for O2. Optics is a possibility. This article contains many words you can use for searching http://www.ott.com/download/ldo-white-paper/
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This is a great idea! This will help greatly!
Thank you very much and have a nice day! :)
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CO2 makes water acidic. O2 doesn't really change the pH of water.
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Right! Thank you. I edited the stack.
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O2 solubility in water goes down with temperature. Maybe heat the water to 90 C, and measure the amount of gas that comes out?
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I'm not sure if you're joking or just brainstorming with me haha. At a constant volume (enclosed chamber) I guess I could measure the change in pressure ... Heeeey. This is a good idea :D Thanks buddy!
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And I could use a peltier element for quick heating!
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And use a cheap peristaltic pump with encoder for measuring the amount of fluid I pump. 13$
http://www.aliexpress.com/item/Peristaltic-pump-DC-inkjet-printer-Mabuchi-365-24V-dc-Motor-with-speed-metering/32421623933.html?spm=2114.10010108.1000014.2.6SR6mg&scm=1007.13338.33078.0&pvid=d918efe2-bac5-4fe7-b6b0-1d33e71d4071&tpp=0
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