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Plant (Vegetable) Filters

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  • Plant (Vegetable) Filters

    It is so very common that a person progressing from watergardener to koikeeper tries to compromise along the way by trying to find a way to keep aquatic plants with koi. Marketing to this desire, manufacturers of pond filters have come up with filter models that include a "plant filter", and magazine articles are written about once per year in the mass audience popular mags touting the benefits of vegetable filters, usually in the form of bog gardens through which koi pond water flows. In general, I think all of these contraptions and suggestions are a lot of silliness designed to sell "stuff", and not appropriate for koikeeping.

    In theory, a plant filter would operate to soak up nitrogen from the koi pond, and other contaminants, resulting in improved water quality. However, I have never seen the theory implemented in a fashion appropriate for koikeeping. A successful plant filter would not have very healthy plants. That is because there would be so many plants that their nitrogen needs would be barely met. No plant would be grown in soil. Only inert media sufficient to stabilize the plant would be used. There would be tremendous work in maintaining the plant filter, because all dying leaves and roots would have to be immediately removed. Once a part of a plant begins to die, the release of the stored nitrogen into the system is very quick. Daily clean-up of the plants would be essential. Further, even if located after mechanical filtration, the roots and leaves will gather mulm, becoming the vegetative equivalent of a filter mat. Like any filter mat, they would need to be cleaned regularly. The pots would need to be emptied, the media cleaned of debris and the plants re-potted on a regular schedule. ...So much work to get plants that look poorly!

    Of course, the idea of a vegetable filter is not sold on the basis of poor growing plants, but as a way to have beautiful aquatic plants and koi. Having one's cake and eating it, too.

    So, what's the harm? In most situations, the veggie filter becomes a haven for build up of organic debris, rotting leaves, hydrogen sulfide production in the submerged soils, and all sorts of vermin that wait for the opportunity to parasitize the koi. A few folks may take the effort to minimize the risks, but in the main the chore becomes too much effort and the rotting mess lies just below the beautiful, fragrant waterlily blooms.

    I wish the folks marketing some of these contraptions understood the needs of koi. But, they do not (or choose to ignore what they know), so it is up to the would-be koikeeper to understand that koi are not for water gardens, and half-way measures are only that.

    P.S. I enjoy my waterlillies. They are in their own little pond where they can be potted in proper soil, fertilized when I feel like it and get all the sun they need to thrive.
  • #2

    Good Job. You hit on the most overlooked aspect of veggie filters. If you do not remove vegetative matter from the system, there is not net export of nutrients. With no net export, there is no benefit. You really need to remove vegetative matter before it dies or turns brown because, by that time, a lot of the nutrients have already been released back to the system.

    If determined to use a veggie filter, I think water hyacinth is the best option because:
    * water hyacinth float up off the bottom so there is minimal trapping of debris and clean-up is easier;
    * they do not need a substrate;
    * they are easy to remove without making a mess - just grab a double handfull and toss them on the compost pile;
    * they are more efficient at scavenging nutrients than most aquatic plants;
    * they may not look good in nutrient-poor water, but they still grow;
    * they do best in full sun but will still grow in mostly shade.

    A veggie filter does one thing that a biofilter cannot do - remove phosphate. Green water and string algae can usually grab some ammonia before it gets to the biofilter and can also utilize nitrate, but they cannot flourish without phosphate.

    -steve hopkins


    • #3

      you guys didn't leave me a thing to comment on! Well thought out and completely explained. i hope those just learning who read yet don't comment will take the above to heart. they both nailed this one! Good Job !!!!!
      Dick Benbow


      • #4

        Thom Blishop, who has possibly the most sophisticated koi pond/system, uses a bog planting area, no soil just clean pea gravel as I recall. No sure if the water returns directly to the koi pond though.

        It would be tremendous to have his opinion on this subject.


        • #5

          Arthur: Yes, Thom posted about his experience on another board about a year ago and was going to provide an update after further experience. I've not seen one. At the time his plant filter had been in operation for over a year. He was measuring reduced nitrates from the outflow, however, his nitrate levels are so low that most pondkeepers could not detect the differences with their test kits. As I recall, he was using a lot of reeds. Older stems were removed regularly. He did not have any sediment build-up whatsoever. It would be interesting to learn what has occurred over time.

          Those not familiar with the Blischok pond should understand that it is probably the true state of the art in the world, with huge water exchange occurring continually and based on "manufactured" water.... RO water "re-built" to have every mineral component and parameter precisely as desired, and computer monitored so that nothing occurs without being tracked.
          Last edited by MikeM; 05-22-2005, 12:39 PM. Reason: correct typo


          • #6

            Steve: I agree that water hyacinth would be an excellent way to go if someone wanted to try to implement a true plant filter. When I was a teen, I raised tropical fish in little swimming pools sunk into the ground. Water hyacinth were the only filtration. The roots would fill the pool, becoming loaded with mulm and debris. It was a very effective mechanical filter. I removed about one-fourth per week and sold to a local shop. I'd remove the oldest, largest ones that were getting yellowing leaves. Looking back, it worked pretty well for what I was doing .... there were likely no more than 2 fish per plant (grown from initial free-swimming fry to maybe 2" (larger on Gouramies) marketable size). I did not do much water testing back then, but the parameters must have been pretty good because I grew out better fish than the tropical fish shops carried in stock. Applied to koi, I guess it would take thousands of hyacinth per fish to be equivalent.

            To have an effective water hyacinth filter, no more than 6" of water depth would be needed, but the surface area would have to be huge. I think the goal would be to remove as many hyacinth daily/weekly as matches the weight of food/leaves/etc entering the pond ... all on a dry weight basis. ....For those not familiar with water hyacinth, when dried a plant is as light as a feather. I think there would need to be a bottom drain for the settlement to be discharged. It would be interesting to see what someone could accomplish pursuing a truly scientific approach to a plant filter, but I think it would prove to be far more work than anyone would care to undertake.


            • #7

              Kudos Mike,
              You hit the nail on the head. Too many people trying to re-invent the wheel
              A while back I posted often on the koi board for the Dutch chapter of the ZNA. I stopped. Got so tired of explaining KOI 101 to all the people raving about the new plant filters they were about to build. I would write pages of responses only to be told "Well I'm going to do it anyway" The a couple of days later it would start all over again with a new member. Made me look and feel like some sort of know-it-all. What's to know?
              For the person $20 fish, I say "sure do what you feel is right", why believe me? But to see serious hobbyists absolutely convinced this was the answer to all troubles and would even eliminate the need for water changes just left me slack-jawed. What is so hard to accept?
              The more I see the rest of the koi world the more it becomes clear or me that humble and ignorant as I feel about my knowledge of koi, we are in fact the elite. I'm sure that the average member of this board is infact in the top 10% of the hobby. Simple things like water regular changes, no plants, having a good net, having a q-tank, owning a microscope and having a set of test kits... This will all class a ponder above 90% of the worlds koi owners. Hard to believe isn't it? Is it because we are so good or that the rest of the world is so abysmally bad? I think the latter. Sad really.
              Semper in excreta, sumus solum profundum variat


              • #8

                I find no point in talking sense to stuborn people. You gives then an info but they think you're trying to trade that info for their soul.LOL

                Koi qualities have improved tremendously over the years. What we learn in old school is no longer enough to maintain the high quality koi of today. What was once the norm is no longer enough for all the reasons you know.
                Filtration systems must be build in a way that truly matters. Gadgets is not enough. Not even close.



                • #9

                  For almost a year now I have been trying to grow plant without success yet. I have a big last chamber, 4 x 1.2 x 0.8 m, where water falls about 25 cm to the pond. In that chamber I have tried all sort of local plants. Even water hyacinth did not survived - after initially seemed to grow and increase in numbers, then slowly turned yellow before finally dried up. Not enough nutrients maybe?


                  • #10

                    If was due to too little nutrient, congrats on your system!

                    But the fact the hyacinth grew well and then failed completely makes me think something else is involved. There are parasitic insects that have been released in Florida in an effort to control hyacinth, which clogs waterways across the entire state. The insect controls have not worked in nature, but there are times when the bugs reportedly do work to decimate small, localized populations. The ones I'm familiar will create chewed areas at the base of some leaves, and even inner leaves will rot off at the base, not just old outer leaves. Perhaps something similar is in your area.


                    • #11

                      Kiky (and MikeMc),
                      I think the hyacinth eventually failed because it depleted its reserves not due to a insect. As in all probability the insect needed to damge Hyacnth would have been brought in with the host plants.

                      One point not mentioned and the reason I am suspect of veggie filters is that plants have many other by-products from their metabolism, and these may (and should in some cases) be harmful to fish. Most terestrial plants release thes byproducts into the air BUT ALSO THROUGH THEIR ROOTS where a host of bacteria live off of them. In water plants the by-products/toxins are most effieciently released into the water..I don't like the idea.


                      • #12

                        Hyacinth are also very susceptable to spider mites. In severe cases, you can see the "webs". In all cases, the underside of the leaves become streaked with a bronze color before dying. The mites are not usually a problem when there is a lot of rain as it literally washes the mites off into the water. The plants can also be sprayed with a garden hose to control the mites.

                        -steve hopkins


                        • #13

                          Unfortunately I did not make a thorough examination when I got rid of the water hyacinth. So I have no idea whether it was caused by insect, spider mites, or other reasons. But as I said, other plants also cannot flourish; unless there was some soil for the roots. Maybe there is some other explanation?


                          • #14

                            Bumping it up


                            • #15

                              Bumping to the top to reply to Sharpey's question to B.Scott in another thread.


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