# What effect does UV have?



## idris (4 May 2011)

My pond pump has a UV tube in it. Having had a couple of pump related problems recently I noticed the UV tube was blown so changed it. The difference to the water clarity has been amazing (and positive) in only 48hrs.

AFAIK there is no suggestion that it kills the bacteria you want, but that it kills algae. Yet planted tank folk seem to think it's a bad idea. 

So I'm wondering what the UV is killing and why that isn't transferable to tanks.


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## foxfish (4 May 2011)

I am not sure if UV light actually kills algae but more like it damages the microscopic spores & in turn causes them to clump together so the mechanical side of filtration can then filter the free floating algae out of the main water body. :? 
One thing is for sure UV tubes have a short life & only remain effective for 4-6 months.
The UV light has to be in very close contact with the algae so they have no effect of blanket weed growing on the side of ponds only on free floating algae (green water).
In fact in a pond situation UV units can promote the growth of blanket weed by increasing the waters clarity & therefore allowing more light in to the water!


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## bigmatt (4 May 2011)

I don't think planted tankers (?) oppose UV, i think it's more that there was some (apparently erroneous) thought that UV destroyed nutrients.  Also there's a question about how effective these ligths are in the planted tnak as we typically have such high turnover that the water isn't in contact with the UV for enough time for it to have any effect (at least if the UV is mounted inline with normal filtration systems).  I think people have had success with "dedicated" UV systems for bad green water
Hope this helps,
Matt


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## dw1305 (6 May 2011)

Hi all,
Assuming the flow is shallow, and relatively slow, the UV lamp will potentially kill all cells that flow through it. UV lamps provide a radiation at a wavelength of about 254 nm which damages DNA and RNA, and they can be used for sterilising drinking water etc.  <http://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiation>.

In ponds the lamps kill the green water algae like _Chlorella_ and _Volvox_, as well as any planktonic micro-organisms (_Euglaena_ & _Daphnia_ etc.). Because photosynthetic micro-organisms tend to be well up in the water column they tend to be preferentially killed. As has been said they only effect planktonic organisms, their effect on benthic organisms, attached algae etc is non-direct. 

The real problem is that this is a cosmetic effect, the "Green water" algae is there because of the combination of nutrients and light, you haven't removed either of these, you have just removed their visible result. If you can reduce the nutrient input, encourage organisms that eat phyto-plankton, or grow a greater biomass of other photosynthetic organisms, the green water will go away. If you keep fish like Koi carps or Gold-fish the problem is that  they will tend to eat macrophytes (higher plants) and zooplankton, so that the end result of using the UV filter will be a greater growth of filamentous "blanket weed" algae. All the time the potential for plant growth is still there, plants will grow.

A better approach to water quality is to use a planted fish free basin as a phyto-filter, If this is planted with fast growing plants (like Reeds _Phragmites_ or Eichornia (Water Hyacinth) etc.) this will convert the nutrients into reeds/Water Hyacinths, that can be easily removed, exporting your nutrients and these will also provide a refugium for zoo-plankton like _Daphnia_ which will eat the green water phytoplankton. If you don't mind frequently cleaning the filter, an over-sized pond filter with a fine sponge will also catch the algal cells, allowing their removal.

cheers Darrel


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## idris (6 May 2011)

Darrel, not sure I understand what you mean by a "phyto filter" of how to set one up. 
The main pond is about 15' x 6' x 2' with a smaller pond about 2' x 2' x 8" feeding it from about 5' above via a water fall. There's a pump in the bottom of the main pond which feeds into the small pond via a canaster filter (with built in UV).

Could I use the small pond as the phyto filter by just putting water hyacinths etc in it, and would it be big enough without having to have it entirely turned over to plants. 

(FWIW It's a very very low maintainence set up - I try to clean the filter out every 2 or 3 weeks, but that's about it.)


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## dw1305 (6 May 2011)

Hi all,


> Could I use the small pond as the phyto filter by just putting water hyacinths etc in it, and would it be big enough without having to have it entirely turned over to plants.


 Yes, but you might need to add some planted plants and/or biological media as well, dependent upon the bio-load. How about some  pea gravel and some potted Irises?

cheers Darrel


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## idris (6 May 2011)

I've got 3 or 4 potted Irises in the main pond at the moment (although they need weeding and repotting) along with some struggling lilies. 
The small pond has pebbles all over the bottom (1" - 2") and I have a bin full of gravel I was planning to put in the main pond. 

In terms of bioload there are about 20 fish (Goldfish, Sarasas and Shabunkins) upto about 4" or 5" and a gazillion frogs along with a good number of Damsels each summer.

Should I put the gravel and plants in the small pond or have them in the main pond?


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## dw1305 (9 May 2011)

Hi all,


> Should I put the gravel and plants in the small pond or have them in the main pond?


I'd put the gravel in both ponds and plants in the top pond, particularly if the Gold-fish eat them. If you can get enough plant biomass growing that should clear the water. I just have my Irises (_I. pseudacorus_ and I. versicolor) planted into gravel, that way the roots have to get all their nutrients hydroponically from the pond water. It also slows the growth of _I. pseudacorus_ down a bit.

cheers Darrel


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## bigmatt (9 May 2011)

It's not fair. I want  a pond!  in fact i want two ponds! 
M


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## idris (11 May 2011)

Thanks Darrel

Not aware of a problem of fish eating the plants.

Would it be better to have the plants in gravel rather than in gravel filled baskets (as they are at the moment)? They're easy to haul out of the pond for maintainence at the moment, but the do get overgrown with weeds.

And does slower growth result in shorter plants? That would be an advantage in the small pond feeding the waterfall.

(If anyone is reading this thread and wishing it hadn't gone almost entirely off-topic, I appologise ... but's is my thread )

Bigmatt - I can lend you a shovel


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## dw1305 (12 May 2011)

Hi all,


> Would it be better to have the plants in gravel rather than in gravel filled baskets (as they are at the moment)? They're easy to haul out of the pond for maintenance at the moment, but the do get overgrown with weeds.


Doesn't really matter whether they are in baskets or the gravel, you want to encourage root growth, so in the gravel is probably better. Mine mainly started in baskets, but they are all well and truly into the gravel now. 





> And does slower growth result in shorter plants? That would be an advantage in the small pond feeding the waterfall.


 Pretty much, I've got Flag Irises (_I. pseudacorus_) in the pond in the gravel terrace, and they are much shorter than they would be in more nutritious soil. Their growth will be a good measure of the nitrogen present, more growth = more nitrogen in a pretty well linear relationship.

cheers Darrel


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## idris (12 May 2011)

Thanks.


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## foxfish (12 May 2011)

I built a few so called "vegetable filters" on some Koi ponds.
I found they worked to a degree depending on the system & exactly what you expect.

There are a few "natural swimming pools" around my way, they operate on two thirds being a planted area & one third being the swimming area.
I built one of them & to the designers specification but, in took 4 years before the water really became crystal clear & even then maintenance is quite high!
I found with the koi ponds, that water cress in a gravel bed worked best.
 It was possible to completely remove about half the cress on a weekly basis in the height of summer. this seemed to definitely work by reducing the build up of nutrients I guesse?
Anyhow most of the more recent ponds I built were plant free & relied on UV + mechanical filtration however the old style vegetable filter models are still going although they also still employ UV in the sytems.


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## bigmatt (12 May 2011)

can you lend me a garden?


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## idris (12 May 2011)

If you want to look after my pond you're welcome.


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