UV De-chlorination for a fish tank?

I did some research and saw other instructables that showed how to possibly create a UV sterilization.

I read that UV light in the 230 and 360 range can break down Chlorine and Chloramines.

I was curious if someone could share how to create a UV de-chlorinating chamber (2-5 gallons) with the use of UV LEDs. For safety purposes I was thinking of a plastic 5 gal bin, where placing the top on the bin completes the circuit to expose the water to the UV light in a safe manner.

how many would be needed? how long would water need to be exposed?


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frollard7 years ago
UV leds don't put out the kind of uv that does any sterilization - its the near-visible blue/purple wavelength that is mostly for visible appeal.  You need a UVB source like a fluorescent tube to get the stuff you want.

I've never heard of uv breaking down dissolved chlorine...it might speed up the process of it gassing off - but it would be mostly a removal of bacteria kind of thing.
Chlorine is an element; you can't "break it down" by pumping energy into the water. At most you can dissociate it from other things (the chloramines?) and _maybe_ encourage it to come out of solution (though I'd be a bit surprised by the latter).
That's what I was referring - you can't chemically change the nucleus without uuber-millions of degrees...or a particle accelerator :D

I didn't specify "compounds" - being the important part, good catch.
jc.021286 (author)  frollard7 years ago
Thank you for the posts

Between the wavelengths 180 and 400 nm, UV light produces photochemical reactions that dissociate free chlorine to form hydrochloric acid. The peak wavelengths for dissociation of free chlorine range from 180 to 200 nm, while the peak wavelengths for dissociation of chloramines (mono-, di- and tri-chloramine) range from 245 to 365 nm. Figure 1 shows the UV output of a high intensity Hanovia medium pressure UV lamp. Up to 5 ppm of chloramines can be successfully destroyed in a single pass through a UV reactor, and up to 15 ppm of free chlorine can be removed.(1)

(1) http://www.wwdmag.com/Using-UV-for-dechlorination-article8635
NachoMahma7 years ago
.  Even assuming that UV will cause the Chlorine and chloramine to come out of solution, it's going to take a lot of power. A few LEDs isn't going to do much good.
.  Letting the water sit for 24-48 hours will get rid of most Chlorine. It may require aeration and/or heating to get rid of the chloramine (wasn't much chloramine used when I was keeping fish tanks, so I don't have any experience with it).
You can get UV-LEDs down to 200nm, I don't know what kind of power you need, or what you could afford ! Short wave UV doesn't pass through water very well at all, and UV sterlisers usually have a thin film of water pumped over the source - with the UV source inside the pipe. There're good reasons why fluoros are used for UV-B generation....

STeve