UV Positioning

[Basil]

Every diagram I have seen of gravity fed systems shows the UV system after the filter retiring to the pond. Is there any issue with installing it before the filter, which would involve taking 4 inch pipe to 2 inch pipe for the UV?

 

[Meyer Jordan]

It is installed after the filter because you want the water passing through the UV to be as clear as possible. Any suspended solids in the water will block the effects of the UV and can greatly diminish its performance.

 

[Jhn]

You want the uv light before the filter, so the filter is catching what is killed by the uv light. If it is after the filter, whatever it kills will just be adding nutrients back to the pond. Kind of defeats the purpose of the uv light if put in incorrectly, since most buy them to clear green water.

Edit...Meyer shouldn't there be some sort of filter after it as well the to keep the dead algae cells from returning to the pond.

 

[Meyer Jordan]

Here is one source that basically says that it doesn't really matter where it is placed.

.Meyer shouldn't there be some sort of filter after it as well the to keep the dead algae cells from returning to the pond.

If you had a filter capable of filtering out dead algae cells, it would be able to filter out live algae cells negating the need for a UV.

 

[Basil]

Thanks for the comments - I do find this interesting, as on the Oase web site they dont seem to think it matters - A quote from their top fo the range "Gravity" UV unit "Extremely easy and flexible installation before or after the filter system"

 

[Jhn]

If you had a filter capable of filtering out dead algae cells, it would be able to filter out live algae cells negating the need for a UV.

Yep, that makes sense. Never mind me, it does make more sense to keep the filter before as you suggested to provide clear water to pass by the uv light.

 

[Meyer Jordan]

Yep, that makes sense. Never mind me, it does make more sense to keep the filter before as you suggested to provide clear water to pass by the uv light.

Not trying to confuse things but one other major factor that influences the efficiency of a UV unit.....that is DOC (Dissolved Organic Carbon). The higher the DOC level the less effective a UV unit will be.

 

[Jhn]

Not trying to confuse things but one other major factor that influences the efficiency of a UV unit.....that is DOC (Dissolved Organic Carbon). The higher the DOC level the less effective a UV unit will be.

I need to not post after bed time or 10pm, since my brain seems to stop working somewhere in that time frame.

 

[moby]

Why do filters with the UV's built in have the water passing by the UV first and then going into the filter material then? I was always led to believe that the UV had the action of clumping the algae cells together to make them physically larger in size than their usual single cells in order for the filter pads or whatever to be able to 'catch' them more efficiently?

 

[Meyer Jordan]

Why do filters with the UV's built in have the water passing by the UV first and then going into the filter material then? I was always led to believe that the UV had the action of clumping the algae cells together to make them physically larger in size than their usual single cells in order for the filter pads or whatever to be able to 'catch' them more efficiently?

What UV unit dies to algae is to render the it unable to multiply.by causing cellular damage. It does not enable any clumping.