Any truth in this statement

[Country joe]

I had an email from a aquarium plant company about getting rid of green algae,which I don't have,
What I found interesting, is what they said after getting rid of the algae,
They said to turn your uv lights off, as it neutralises filter bacteria, and kills of nutrients for plants. Is this correct,as I run a UV light.

 

[Essjay]

It can't kill the filter bacteria, assuming that the UV light unit is inside a casing. The UV light can only kill bacteria which flow inside the casing and as the filter bacteria are attached to surfaces they never get exposed to the UV light.
If the UV light is exposed to the water, then yes it might affect all bacteria in the tank but an exposed UV light is a very bad idea both for the fish and humans looking into the tank.

It won't kill off plant nutrients as they are not alive. But yes, UV light can degrade chemicals as they are exposed to the UV inside the casing. However it does depend what exactly is meant by plant nutrients. Minerals won't be affected eg potassium, iron etc.

 

[MaloK]

Yes, UV-C light breaks down chelated complexes and micro-nutrients like iron, zinc, and manganese lose their solubility and actively precipitate.

Also UV-C's degradation of chelates, particularly those involving boron and zinc, might indirectly affect phosphorus uptake by some kind of binding. Not much research on that aspect.

While more research focuses on UV-B's impact on nitrogen metabolism, high doses of UV-C could potentially have an even worse impact on enzymes involved in nitrogen uptake and assimilation in aquatic plants. Due to it's higher energy levels and potential for damaging biological molecules.

Normally once the problem resolved, I wouln't suggest to run UV-C all the time and shut it off until absolutely required again.

 

[GaryE]

@Country joe - this was a great question I was hoping to see an answer like @Essjay's to. I've used a small UV powerhead for disease control. and have seen no reduction in plant growth or water quality with it. But that's pretty anecdotal.

 

[Rusty_Shackleford]

I'm currently running a UV-C clarifier to take care of a stubborn green water issue. There is zero chance an UV unit will effect a mature biological filter, nor will it have ane effect on algae on glass, rocks, plant leaves etc. I also concur with @GaryE about the plant growth.