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While I am a firm believer that plants and Koi can live happily ever after in the pond together and actually benefit each other, I realize that plants in the Koi pond are not for every one. Everyone wants something different out of the hobby whether it is Koi pond that contains show quality fish or a water garden that contains both fish and plants. Many folks enjoy the beauty of the fish and do not want anything to interfere with that view. I suspect and my email agrees many others consider the water garden to be an integral part of the over all-landscaping and do not want or like the sterile look of Koi pond. It is your hobby, do what pleases you and not what pleases the next person.
Plants readily take up and use two forms of nitrogen, ammonium (NH4+) and nitrate (NO3_). In order to understand the nitrogen cycle in our pond it is important to understand that the conversion of ammonium to nitrite and then to nitrate is referred to as the nitrification or more simply the nitrogen cycle.

Koi make ammonia and lots of it. Not only does ammonia come through the digestive tract in the form of urine and feces it also comes through the gills as the fish breathe. Plants use the ammonia, the first stage of the nitrogen cycle, to grow. Look at a bag or a bottle of fertilizer and you will see three numbers on the label. The first number of the equation is ammonia. Remember we add a high ammonia fertilizer in the spring to make the grass green up? Ammonia is what makes plants grow and keep their nice green color. One thing that is really cool about plants is they do not care where the ammonia comes from. The ammonia that pond plants need to grow can come from commercially prepared fertilizer or organic fertilizer from fish waste. And as we all know ammonia is very toxic to fish. One will never see an ammonia reading in a pond that has plants that are actively growing.

The final stage of the nitrogen cycle is nitrates. Nitrates form when the biological filter begins to break down the fish wastes. While nitrates are not harmful in low numbers, after time the nitrates will build to toxic levels. It is generally recommended that nitrates be kept under 60 PPM. Plants and algae, will use the nitrate. In the case of high levels of nitrates where there are no plants present, the algae will form and will cause an algae bloom, the dreaded green water syndrome. There are only two effective ways to remove the nitrates, water changes and plants.

The second and most common way to remove nitrates is through water changes. While water changes should be done on a regular basis in some case it is not practical to do enough changes to keep the nitrates low, below the 60PPM level. Some of the reasons are: water rationing due to drought, not having the luxury of well and septic and paying for city water and sewer usually at a much higher cost than having a well and septic. For some it is a lack of time because we all seem to lead very busy lives. If water changes can not be done on a fairly regular basis than plants can be the solution to keeping nitrates low. Plants can very effectively use/remove nitrates.

Once the water has warmed enough in the spring for the plants to actively grow, they will begin to use the ammonia and the nitrate thus eliminating green water or the need for an UV filter. The whole principal of plants is balance. Each pond is its own ecosystem and one must find the number of plants to keep everything in balance.

The big argument with plants and Koi is that the Koi eat/destroy the plants and make a mess in the pond thereby making more work for the owner. Not all Koi eat or destroy plants and I am not sure why some do and others don’t. Maybe it is boredom or maybe the fact that Koi are "eating" machines. There are ways to keep the Koi and plants together if one is creative. Plant stands either commercially made or homemade can be utilized to keep the plants up away from the fish.

The biggest argument against plants is that it is really hard to keep the water clean from the dirt from the plants. Growing the plants with out dirt can solve this problem. Simply place the plant in a pot and fill the pot with larger rocks.

Many will argue that plants can harbor parasites and bacteria that can be harmful to the fish. Rightly so! Treating the plants in a bath of Potassium Permanganate can solve this problem. Use a hose and wash the all the dirt off the roots and remove any faded leaves. Then make a solution using 20 PPM of potassium permanganate in a large container. Place the plants in the container and add an air stone and let it circulate for a few hours. Now you have clean plants with no parasites or bacteria with not much effort. I do want to caution here, do not use formalin to treat the plants or you will have dead plants because formalin is a herbicide.

Many of those that do not put plants in their pond do use veggie filters or sometimes called a bog filter. A veggie filter is part of the overall pond system but in an area that is not accessible to the fish. It does not contain any soil. The media for growing the plants can be gravel or lava rock or a combination of the two. Some will just use larger rocks.

The diagram below shows how we do our veggie filters. We have used this design for many years with excellent results.

Upflow veggie filterJust like the water garden, the veggie filter needs to be thoroughly cleaned at least once a year. Generally this is done in the fall. This means removing all the plants. At this time you can clean the plants up, trim them back, divide the plants and then place them back in the veggie filter or store them for the winter if you live in a cold climate. One important point is that even if you live in a warmer climate you should still clean everything out at least once a year. Studying the above design you will see that it contains a bottom drain for cleaning out the trapped crud. I would suggest that this drain be opened and cleaned every couple of weeks. But time and experience will tell you how often you should clean it out in your circumstances.

(Click to enlarge photo)

The first thing you need to know is the volume of water the pond holds. To calculate the gallons multiply the length times the width and then multiply that figure by the average depth. This will give you cubic feet. To convert cubic feet to gallons you would then multiply that number by 7.48. Some the basic equation is L x W x D x 7.48

The reason you need to know the gallons is because the veggie filter has to be sized for the gallons of water in the pond. A good rule of thumb is 5 to 15% of the water volume. The higher the fish load the larger you will need to make the veggie filter to work effectively. And if you are a real plant enthusiast, you may want to go the 15% just to have a bigger size that will hold a bigger variety of plants to add to your veggie filter.

The pump size is very important also in your veggie filter. To figure the pump size you would you need to run the veggie filter, multiple the total gallons of the pond time 5 to 15% to determine the size pump you will need. Just to clarify this a little more if your veggie filter is 5% of your pond volume then multiply the pond volume by 5%. If you are building a veggie filter that is 15% the size of your total pond volume, then multiple that by 15%. One other thing to consider is you might want a waterfall that sounds like a mini Niagara Falls. In this case you would use the larger pump size, 15% of the total water volume size to give you the noise.


This is really a matter of personal preference of which plants to use. Some of the plants I have used are Iris, Sweet Flag, Parrots feather, Bluebells, Umbrella palm, Papyrus, Water Celery both the green and the variegated, Taro (lots of choices in this family), and Watercress. Water Hyacinths are a good choice if the veggie filter is in the sun or Water Lettuce if the area is shaded. I do want to add a word of caution about using either of these two floating plants. Since the veggie filter is a waterfall it is important to keep a close eye on these plants. They can dam up and actually divert the water out of the pond.

Here is a fun idea for plants in your veggie filter. Use edible plants. These choices would be watercress, either green or variegated celery, water chestnut, sweet flag, flowering rush, and arrowhead. Do an Internet search for edible pond plants and see what you come up with. When the plants have excessive leaves I trim them off and feed them to the fish and they love the treats! My favorite edible plant to grow in a veggie for is a tomato plant! True hydroponics in the pond. And I feed the fish the leaves and the fruit that we do not eat. Please be sure to skin the tomatoes and remove the seeds before feeding them to the fish.

Experiment! Try different plants in your veggie filter.

A waterfall filter we use in one of the greenhouse fish tanks

Here is a simple waterfall barrel with an Umbrella palm.  The water falls back into the pond or tank. In this case the water is falling into a 500-gallon stock tank. But this type of veggie filter could be sunk into the ground and work as a waterfall in a smaller pond



650-gallon stock tank is full of umbrella palms to help keep the nitrates under controlA larger veggie filter can be made using a 650-gallon stock tank.  This can be a simple as large stock tub or as simple as a wash tub or anything in between. Size will depend on the number of gallon in the pond or tank and fish stocking density. The picture below is a 500-gallon stock tank purchased at a farm store. It flows into a 4,000-gallon tank that is generously stocked with fish.


At the end of the season the umbrella palms were 6’tall and 5’ across. And the fish had the benefit of no ammonia or nitrates the entire season.
This tank also has a bead filter that filters 1,000 gallons and a home-made box filter that does 100 gallons of filtration Water fall filter on a 350 gallon stock tank.  This tank also has a bead filter that filters 1,000 gallons and a home-made box filter that does 100 gallons of filtration
100-gallon tank has 2 home-made box filters.  Each box filter will filter 100 gallons of water each 100-gallon tank has 2 home-made box filters.  Each box filter will filter 100 gallons of water each


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