# [Wet Thumb Forum]-UV Sterilizer



## indy (Feb 28, 2005)

I heard or read somewhere that a UV Sterilizer will distroy certain eliments that are needed by plants? Does anyone no if this is true?


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## indy (Feb 28, 2005)

I heard or read somewhere that a UV Sterilizer will distroy certain eliments that are needed by plants? Does anyone no if this is true?


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## noah_greenberg (Aug 20, 2004)

Ive heard from others, and experienced for myself that when I am running my UV bulb I have to add Fe almost daily. Im not aware of N,K, or Ph drawdown with the UV filter. If you can, run your UV filter only when needed and dose accordingly. 

Good Luck!

Noah


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## indy (Feb 28, 2005)

I found this in the artical about algea, I guess this somewhat answers my question..

Quote:
For fish only tanks, a properly set up ultraviolet sterilizer will kill algal spores in the water and prevent them from gaining
a toehold. For planted tanks, this is not a good solution since the UV light will also oxidize trace elements needed by the plants and will limit the plant's growth potential.


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## noah_greenberg (Aug 20, 2004)

I have a planted tank and run the UV filter a week every two months or so, usually after a big waterchange/re-scaping AND whenever I add new fish/plants to the tank. This has worked well for me so far. When it is running, I dose trace elements daily and the plants dont seem to suffer.


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## Tonka (Mar 20, 2004)

In a mature planted tank a UV sterilizer should be turned on only when fighting suspected fish disease or bacterial/algae blooms. If it's on a week, plants will not be affected by any supposed loss of complexed inorganics.


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## Margolis (Sep 22, 2004)

I've had problems with this idea of uv sterilizers oxydizing trace elements for a long time now. How exactly can uv light oxidize anything? Oxidization is a reaction of oxygen not light.

anyway, I run my uv sterilizer 24/7 now. I tried it with it off for a while and with it on all the time. I have seen no noticable or measurable difference either way. I did notice the water did not stay quite as sparkling with it off though. So I would say use it 24/7/365


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## noah_greenberg (Aug 20, 2004)

You could run your UV bulb that often, and replace it four times as often as I do! I don't know about you, but those bulbs are not how I like to spend my $30.

As for the oxidising: I think that UV light with its short wavelength and high energy is capable of breaking down oxygen bonds (makin 02 into 20) and these free radical elements (one molecule of oxygen alone is not stable) will bind to iron rendering it oxidized and unavailable to plants.

If I am wrong, please correct me.


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## Roger Miller (Jun 19, 2004)

Margolis, "oxidize" does not just refer to reactions with oxygen. In the simplest case it refers to any reaction that causes an ion to lose one or more electrons and gain a more positive charge. When an ion gains an electron it is said to be "reduced." In the case of organic molecules (where it is hard to define the state of individual ions) oxidation normally implies the loss of a hydrogen atom, while reduction implies the gain of a hydrogen atom.

UV (or other wavelengths) can cause an oxidation reation when a photon of light is absorbed by the valence electrons of an atom. That increases the energy level of the electron. If the increase is sufficient then the electron can jump to a new energy level in the atom or it can break completely free of the atom. In the first case the electron normally releases a photon and falls back to its original energy level. That is the process of fluorescence. The second case is photo-oxidation.

What happens depends on the energy of the adsorbed photon, on the energy level of the adsorbing electron and on the size of the energy step that the electron has to reach to either jump to a new level or leave the atom entirely. Nothing much at all happens without the right combination of photon energy and an atom with the right electron energy levels.

A few years ago Paul Sears posted a letter to APD claiming that oxidation wasn't a problem for any trace element other than iron. I might add manganese as a concern, but otherwise agree with his statment. Oxidation is not a problem for most trace elements. That should be true whether we are talking about photo-oxidation or chemical oxidation.

Ferric iron chelates are another problem. Photo-oxdation of the chelates actually effect the organic chelating agent, not the iron. The iron is reduced when the chelating agent is oxidized. The photon energy necessary to break down a ferric chelate is (I believe) a blue light. UV light may be more than sufficient for the task. The UV light might cause an accelerated rate of breakdown in chelated iron. the photoreaction leads to elevated levels of ferrous iron in solution and relatively rapid disappearance of the chelated iron. I suppose you could look at that as choice between a "glass half full" and a "glass half empty" as the result is partly favorable and partly unfavorable.

What that means to your tank I don't know. It seems to me like an issue best left to those with specific experience.


Roger Miller


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## Margolis (Sep 22, 2004)

thanks for the explanation Roger, greatly appreciated


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## indy (Feb 28, 2005)

Thanks alot Roger, I think what I'll do is use the UV sparingly, like if I gat an algea bloom or disease..


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