How long does a UV clarifier take?

Discussion in 'Pond Archive' started by lawr_1, Apr 5, 2008.

  1. lawr_1

    lawr_1 Guest


    I only have a 1064L pond (about 1.4m x 1.9m x 0.4m), and have been
    trying for a year and half to make it clear naturally. So have pond
    plants and a normal bio filter (one of them boxes with foam and
    sections of pipes in it). But have failed to clear it naturally so
    installed a Tetra 9W 8000L UV clarifier. Its installed just before the
    water goes into the filter.

    The guy at the garden centre said it should take 4 to 5 days and it
    will end up crystal clear. But its been on about a week now and I cant
    see any difference, pond is still pea soup. I can only see an inch or
    two down.

    The filter light is on indicating it working (although I assume UV
    light is invisible so I cant tell if the bulbs are working but the
    bulbs dont look broken). I dont know what pump is being used.

    I wondered how long these things usually take to work? And if it
    clearly is not working what could cause it to not work considering the
    UV clarifier is working and the bulbs dont look broken.

    lawr_1, Apr 5, 2008
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  2. lawr_1

    Pond Addict Guest

    That's interesting... My Aquaultraviolet UV said to install it just
    *after* the filter, on the return...

    The thing about UV is that the bulbs really need to be replaced every
    year because they become ineffective, and it's really important to get
    the right amount of UV for your pond size. I always oversize these
    things. It's also important to have the flow high enough so that the
    water is getting changed over at the correct rate too. I'm not sure of
    the requirements or size limitations for the Tetra UV. 9 watts seems
    really small, but maybe that's because I'm used to a larger pond.

    The first thing I'd verify is that you really want to put the UV
    *before* your filter. Doesn't UV kill the good bacteria? Then check
    the flow requirements for the UV and the pond size limitations.

    Oh, and for mine, it takes only a few days to notice a big difference.

    - Dave
    Pond Addict, Apr 6, 2008
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  3. lawr_1

    Pond Addict Guest

    Hi, I have a little more info on this.

    I checked the manual for my UV, and it says that the best place to
    install it is after the filter.

    "If an after filter installation is not feasible, your sterilizer can
    be installed before the filter, but it will take a little longer to

    The unit I have can be used to clarify or sterilize, so that's why
    it's referring to the unit as a sterilizer. It goes on to say that if
    you do a pre-filter installation, you should be aware that even a
    small stone can pass into the unit and cause breakage. Good point.


    "Ultraviolet light does not discriminate about what it destroys. If
    good bacteria passes by the light it will be destroyed."

    So, the takeaways are: It takes longer for a clarifier to work if it's
    before your filter, there's more risk of breakage if it's before your
    filter and it will kill good bacteria if it passes through. Normally
    the bacteria won't be free floating like that, but if you're seeding
    your pond and your filter with bacteria, you'll want to keep the UV
    off until they've colonized in your filter and on the pond walls.

    Maybe it's just your placement of the UV that's making things take
    longer. If you really have pea-soup water, you'll need to be actively
    cleaning your filter, since it should be filling up with the dead
    stuff. I'm not sure what kind of filter you have capacity-wise, etc.
    but that may be a consideration as well.

    My first pond was installed by a landscaper who didn't specialize in
    ponds. I was naive enough to believe it when he said he was an expert
    on pond construction. I quickly learned more than that landscaper
    after I ran into problems like green water. In the case of that pond,
    the pump was undersized for the pond size, the "filter" was one of
    those small pass-through filters that sits on the bottom of the pond,
    and the pond was put smack under several healthy pine, sycamore, and
    maple trees, which made for a memorable Fall clean-up.

    The next summer, I ended up enlarging the pond (just cuz), adding a
    skimmer, adding a bead filter, adding UV and tossing the pond-bottom
    filter. I suppose those work for very small ponds, but I wasn't
    impressed with the one I had and they're a pain to clean. That pond
    was about 3,500 gallons and the filter was useless for that. Without
    mentioning any names, it's the same kind of "pond filter" you can find
    in your local pet store.

    That pond was still a pain because of the trees, but the skimmer was a
    godsend and the UV, larger pump and better filter kept the water
    clear. The combination of flow, filtration and UV (if you opt for it)
    is important, because the whole system needs to be matched. A wimpy
    pump on a beasty filter or correctly-sized UV will not do much good.
    So, try to make sure that all the pieces are spec'd for each other. I
    mentioned before that I tend to oversize all these things and that's
    because I've found that it doesn't take long before you have more fish
    in the pond than you ever intended. Fish aren't big on abstinence.
    Over-sizing the filtration and such gives you a little more time to
    deal with that inevitable problem.

    Anyway, I hope the extra UV info might be of some use. This is the
    tough time of year algae-wise, so hang in there.


    Pond Addict, Apr 6, 2008
  4. lawr_1


    Pea soup algae grow because there is excess ammonia or nitrates in the pond.
    The filter needs to remove the algae faster than the remaining algae can reproduced
    due to the excess wastes.
    OR, reduce the waste load. How many fish in this 280 gallon pond?
    UV doesnt kill the algae, it clumps them so they are less likely to slip thru the
    filter. If your filter isnt removing the clumped algae, then they putting the
    nutrients right back into the pond. If you put polyester batting into your filter
    you will remove that algae, but then you need to take the batting out when it is
    loaded and either clean it (squeeze into clean water) or toss it and add more
    A UV filter does work better after the filter if there are a lot of "solids" in the
    water. Other "stuff" protects the algae from the UV.
    Often the glass in the chamber that holds the UV bulb becomes clogged with algae,
    etc. so it is necessary to clean the "window" or the bulb itself. UV lights can
    last years as long as other measures are taken to keep waste levels low. Like a
    veggie filter.
    , Apr 6, 2008
  5. lawr_1


    They dont become ineffective in a year.
    The slower the flow the more likely that the algae will be exposed the correct amount
    of UV to cause clumping.
    the good bacteria are not in the water, they form colonies ON the biofilter material.

    It's also important to have the flow high enough so that the
    Doesn't UV kill the good bacteria?
    , Apr 6, 2008
  6. lawr_1


    It is unlikely that anybody is going to shell out the money for an actual water
    sterilizer for the pond. Nor is it necessary.
    My UV has its own itty bitty pump, a maxi 1000
    this clears algae out of a 1600 gallon pond. I have a big pump for my veggie filter,
    altho that too may be oversized but it gives a nice waterfall on the other end.
    , Apr 6, 2008
  7. lawr_1

    lawr_1 Guest

    another question though... is UV light invisible? I just found one
    website saying you can monitor the light through the inlet/outlet. I
    thought it was invisible. If you can see it them my clarifier is not
    emitting any visible light.
    lawr_1, Apr 6, 2008
  8. lawr_1

    Hal Guest

    If you don't know how much water the pump is flowing through the UV,
    you might have missed an important requirement of UV clarifiers. The
    water flowing through the filter has to be in contact with enough UV
    to work. If the water flows too fast it doesn't have enough UV light
    contact. I doubt the flow is too slow, that would cause the UV to
    kill algae and more types of bacteria too. This chart indicates the
    max flow of your pump would be 900gph. Your 1064L pond is about the
    size of my hot tub pond and I'm running a 1200gph pump on it, so I
    would have to reduce the flow or get a larger UV clarifier for my set

    You might have better luck at seeing the blue light coming from a UV
    clarifier/sterilizer at night. (My bulb is rated for 11 months use
    and comes with a caution that it is harmful to eyes and skin, so I
    wouldn't spend a lot of time looking for it in the daylight.)
    Hal, Apr 6, 2008
  9. lawr_1

    Pond Addict Guest

    I've noticed a dramatic difference with bulbs that are old vs. new,
    and the material I've read does say that the bulbs become ineffective
    after about 14 months of use (so maybe every two years). Yes, they
    still light up, but they're not doing what they're supposed to be
    doing. My experience backs that up. I expect that the bulbs don't just
    suddenly become ineffective one day, but rather it's a gradual decline
    over time. Replacing them earlier may not strictly be necessary but it
    can improve performance.

    My UV sterilizer has wipers on it, and the chambers are most
    definitely not filling up with algae. Rather, the bulbs themselves
    become less effective over time. However, in a situation where the UV
    is before the filter, I think you could have a major "gunk up" problem
    that would make the unit ineffective.

    The "sterilizer" vs "clarifier" difference is only based on the size
    of the unit compared to the size of your pond. I agree you don't need
    a unit acting as a sterilizer, but a sterilizer is just the same
    "clarifier" unit, handling a smaller water capacity. At least that's
    how the Aqua Ultraviolet units are.

    You're right, the UV doesn't kill the algae, it sterilizes the free-
    floating stuff. It kills smaller things that pass through it such as
    bacteria, viruses, fungi and so on.

    I'm surprised to hear that you need UV with a vegie filter. Isn't the
    veggie filter alone enough to control the algae or do you use the UV
    for other reasons?

    - Dave
    Pond Addict, Apr 6, 2008
  10. lawr_1

    lawr_1 Guest

    I'll have to see if I can find the pump flow, maybe it is too fast.
    The bulb is clean, I removed and checked it yesterday, there was no
    build up.

    One issue I found... I cannot see any UV light. At the inlet and outlet
    I have a section of clear pipe I have used to connect the outlet/inlet
    to my pump/pond hose (it was too big for a standard garden hose size
    and B&Q didnt have any adapters - I had to cut up my snorkel to make
    it). So its night now, and I can bend the clear pipe connector down a
    bit to look right into the UV clarifier outlet while the water is
    flowing. It is completely dark, no light at all.

    Yesterday I took the bulb out to look and it doesnt look like its

    So could the bulb be faulty? Should I see UV light? I am not looking
    long as I know its harmful.

    If you cant see the light the only thing I can think of is my flow is
    too fast.

    Or am I expecting too much in 1 week? Should I give it more time?

    Thanks for your replies.
    lawr_1, Apr 7, 2008
  11. lawr_1

    Hal Guest

    Even though we use the bulb for the UV, I doubt one can be reasonably
    priced that is invisible. Mine emits a blue light. I did use a small
    length of clear tubing on either side of the clarifier so that I could
    see if the bulb is working and it shows up well at night. The UV
    bulbs are sensitive to moisture in the chamber and mine blows a bulb
    at a figment of the imagination.
    Hal, Apr 7, 2008
  12. lawr_1

    Pond Addict Guest

    My bulbs glow blue as well. In bright (ambient) light that can be hard
    to see, but it's very apparent in low light.

    Pond Addict, Apr 7, 2008
  13. lawr_1

    RichToyBox Guest

    The light emitted from a uv bulb is both uv and near uv, meaning it has a
    bluish cast. You should be able to see it through the clear end caps. If
    you cannot see any light, then the bulb is bad or the ballast is bad. If
    this is a new unit, take it back.

    Zone 7A/B Virginia
    "lawr_1" wrote in message
    RichToyBox, Apr 7, 2008
  14. lawr_1

    lawr_1 Guest

    I checked my pump, its a Hozelock Cascade 1400 which pumps 1400 litres
    per hour, but the recommended for the UV clarifier is Tetra Pond FP
    2500 which pumps 2500 litres per hour.

    So it looks like its not to do with too fast a flow. I would have
    thought a slower flow means more chance of UV working?

    So therefore should I see the UV light as there is none showing. Its
    the last thing I can think of, that the bulb is not working or

    lawr_1, Apr 7, 2008
  15. lawr_1

    lawr_1 Guest

    Apparently the LED on the side is not an LED but a viewing window for
    the UV light. So this is bright blue. So apparently the UV is working.
    Its just that no light is seen through the inlet/outlet. At the outlet
    the bulb is blocked by an inner part but I would have thought the inlet
    would emit some light. Either way apparently its working.

    So I have replaced the filter material in my filter because someone
    else said this needs to be working too to filter out the clumps of
    algae that the UV produces. I think it was quite old and clogged. So
    maybe thats the reason.

    I also drained the pond and refilled and will see if this helps.
    lawr_1, Apr 8, 2008
  16. lawr_1


    I have a veggie filter for 6 months of the year. I feed my fish for 11 months of the
    year. by spring I have pea soup and it takes time from April until almost June for
    my filter to get going.

    HOWEVER, this year I put a little veggie filter IN the pond over winter and left the
    pump in a bucket filter which has screening and matting in it and there doesnt appear
    to be much algae at all. The water isnt clear it has "fines" in it most likely
    because the active koi have been digging in my lily pot.

    What is really amazing is that last fall I didnt clean and empty the veggie filter of
    all the water celery and one flower pot and the water celery is already as high as it
    is in May and pushing up under the plastic. So this may be a huge jump start on the
    veggie filter. I am shocked because this was a hellatious long cold winter. That
    water celery is amazing stuff. I expect that when I switch the water thru the veggie
    filter it will quickly trap the "fines" and clear up the water.

    anyway. I use the UV to clear up the water in spring before the veggie filter gets
    going. I wont turn it on at all this spring unless algae shows up. Ingrid
    , Apr 8, 2008
  17. lawr_1


    like most bulbs, they arent like a laser producing a pure wavelength but a wider
    spectrum so they generate a bit in the high blue end so there is a bluish color.
    , Apr 8, 2008
  18. lawr_1


    slower the better. but it has to stay ahead of the algae replicating and algae
    growth depends on many factors.
    , Apr 8, 2008
  19. lawr_1

    lawr_1 Guest

    Yeah, I think I have established that it IS working and glowing, just
    difficult to see anywhere other than the little view window (which I
    thought was a LED not the actual UV).

    So I dont think its the UV clarifier. So I have replaced the water in
    the pond and replaced the filter media in the biofilter. Its still
    quite murky because I didn't clean the pond completely or swish out the
    bottom of the filter, but its much better.

    So I need to monitor it to see if the UV clarifier and cleaner
    biofilter combination improve it now.
    lawr_1, Apr 8, 2008
  20. lawr_1

    Pond Addict Guest

    I was just re-reading the original post of this thread, and it makes
    me wonder if you're pump/filter combination is really up to the job.
    If the filter isn't doing enough, UV isn't going to help.

    What kind of filter is it, and is it in-pond or out?

    Before you changed the water, did you do any water tests? Those would
    undoubtedly show excessive ammonia or nitrates, like Ingrid said. I'd
    guess with so much algae your PH is climbing too. That's something to
    be careful about if you're doing massive water changes since you could
    cause a wild flux in PH.

    It really sounds like your filtration isn't enough to handle your fish
    load. Are there a lot of fish in this pond? If so, you'll need beefier
    filtration unless you can remove some of the fish.

    Pond Addict, Apr 8, 2008
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