Consultant René visits two ponds where things almost go wrong
I will take you on a tour with the Koi and Pond Advisory Group to two ponds. Here is, as I call it, filing on the edge. Again, I hope to discuss two instructive points. It may make sense to some, but to others, it is a boost and motivation to adjust their methods just a bit.
Keeping clean
The first pond is a beautiful natural pond, which is located in two adjacent backyards in Vlaardingen. Two neighbors who worked together to create a beautiful pond / stream, which has many plants. The fish make a not too healthy impression, something that also worries one of the owners.
The water is checked for quality, which initially looks good. A pH of 7.5, ammonia and nitrite not measurably present and a KH of 5. Nothing to worry about. The filter consists of a four-chamber filter with brushes and mats. The food given to the Koi consists mainly of fun colored sticks that almost blow away when the fish are fed. Not ideal for Koi because these feeds often lack important ingredients, but not the cause of the problem.
The pond contains two corners full of plants. These plant “filters” are full of muck. When I put my hand in the water here, the muck swirls up and forms a cloud of dust. It is likely that in this muck live many bacteria that ultimately affect the health of the Koi.
Upon inquiry, it appears that, the corners where the plants are located are never cleaned. The accumulated dirt had been seen, but considered blubber that plants live in.
It is assumed that bacterial pressure in the pond is so high that it affects the health of the Koi. Small wounds are not given the opportunity to heal as a result, and the health of the Koi slowly declines. Having bacteria pressure measured directly makes no sense here, although it would confirm the theory. It was decided to do a big cleanup right away the next day and use a submersible pump to remove as much muck as possible.
Two weeks later you could already see from the Koi that they were doing much better. Then the bacteria pressure did get measured. This was around 800 Cfu/ml (colony forming units per milliliter,or number of bacteria per ml of water), which is very neat (5000 Cfu/ml is high).
Conclusion: Due to the continuous accumulation of dirt in certain parts of the pond, the possibility has arisen that (incorrect) bacteria will multiply to such a number that the Koi will suffer. Cleaning up and doing substantial water changes helps bring down the bacteria pressure, restoring a healthy habitat for the Koi.
Check the pond and filter regularly for accumulations of debris. If a dust cloud of dirt can be made by stirring the water by hand, then the pond here is too dirty. Look for the cause and try to solve it.
Plant filters are beautiful and in my opinion really add to the experience of water and fish. Plants have a place in the nitrogen cycle where they absorb nitrate and provide nutrition for fish and other animals. Recently, however, the usefulness of a plant filter in a koi pond has been questioned. It is a part of the pond that pollutes easily and thus often causes problems. Moreover, relative to the volume of the pond, the section with plants is often too small to make a real contribution to the nitrogen cycle.
If you do want a plant filter then it is very important that it can be easily and properly kept clean!
As a good example, I would like to show Marco and Kim’s plant filter.
Directly against the pond is a tray made for the plant filter. Some of the water coming out of the filter is pumped into the bottom of this tank. The pipe where the water comes out is along its entire length and is free. This will cause water to swirl around and prevent dirt from making piles.
The plate on which the plants stand contains nice large holes so that no obstruction in the water flow will occur here and the water can flow past the plants into the pond without problems.
The plants are in crates so that they can be easily removed from the filter during the big cleaning, which I recommend doing at least once or twice a year. There are many articles to be found about plant filters and which plants are or are not suitable. Yellow Lis in an example of a plant that grows quickly and therefore uses a lot of nutrition. This is beneficial, making yellow Lis a suitable plant for a plant filter.
Refresh
The second pond is one example among many. The pond in question belongs to Johan. Johan had bought a new house that included a Koi pond. It did have some nice fish swimming in it and Johan allowed them to stay. Last year after the summer, he got the key and started remodeling. As is the case with many moves, the main focus here was on remodeling.
Sometime in April, Johan asked if I could come and have a look, see what he had, how it worked and of course “if it was worth anything.”
After a chat on arrival, the main focus is on the system and its fish. Under the patio is a nice filter pit, which contains a setup with a vortex, three-chamber filter and a UV lamp. As the previous owner handed it over, Johan ponders on. He rinses out the brushes every week. Every month the Japanese mats. The moving bed he doesn’t have to do anything about.
In the pond, which we estimated at 16m3, swam 9 Koi and a sturgeon. One or two of all colors were present. In short, a very nice (average) pond.
Since I had brought my gear for testing the water and checking the mucous membrane anyway, we caught two fish for the study. Good stuff was also available for this. A catch basin (in this case, a clean mason jar), a pan net (shallow scoop net) and a Koisok (scoop net which is meant to be used when fish must be walked on) were available.
A swab is taken of the mucous membrane and a quick look at the gills of the fish. The gills should be nice and red. If not, that’s an indication that there is something wrong with the water quality. Usually in the form of excessive ammonia or nitrite levels.
We view the scraped-off piece of mucus layer with the microscope to test for parasites on the fish.
With these fish, it looks good. An occasional skin worm is found, but that is not reason enough to start treating against it.
By testing the water for acidity, hardness, ammonia, nitrite and nitrate levels, we can make a statement about the quality of the water. However, this one is far from ideal, or better, this pond is on the verge of a pH crash at the time of measurement.
It turns out that in all the months that Johan has now cared for the pond, he has refilled water a total of twice. To keep the water in good quality, weekly changes of about 10% are advisable. Even better is to test the water regularly and make sure that by refreshing the water quality (readings) remain good.
In a pH crash, the pH changes from the desired value (between 7 and 8) to 3 or sometimes lower in a very short time. A Koi can hardly stand changes in pH, and the moment the pH drops that much in a short period of time, it usually kills the Koi. The bacteria present in the filter also do not survive a pH crash, as a result the entire system is dead.
Conclusion: By structurally not changing the water, the water has become so much more acidic that the carbonate hardness of the water (KH) has also dropped to almost 0. There is then no more “acid-buffering” capacity in the water, making it more acidic. The result is a pH crash, which is deadly to fish. This can be prevented by regular changes and measuring your water values yourself. The test kits include guidelines on what values are desired (for which fish). Here, it is especially important that these values remain stable and do not fluctuate too much. Therefore, if you see a value increasing/decreasing a little bit each time you take a measurement, then you will need to change more.
To understand how a pH crash can occur, I will summarize in a nutshell what happens in the pond. There are whole courses on this, but in Jip and Janneke language, it boils down to this:
- The fish pollute the water with their gills and feces.
- Bacteria in the filter convert this pollution from ammonia to nitrite. This will make the water more acidic.
- Bacteria in the filter convert this pollution from nitrite to nitrate.
- Nitrate is no longer toxic and remains in the pond. Aquatic plants grow from this.
- Fish/small animals eat from the aquatic plants.
In nature, this creates a circle which is in balance. However, in our ponds, the ratio of the number of fish to the amount of water is not comparable to nature. In the 2nd and 3rd steps, the water becomes more acidic, which is not measurable in nature, but is in our ponds.
The water also contains KH. This ensures that the pH will not change (much) as long as this KH is present. However, keeping the pH stable will slowly deplete the KH. So, at the time the KH is depleted, the pH will change as a result of steps 2 and 3 from the nitrogen cycle.
The easiest way to replenish KH is by changing water. You remove 10% of the pond water each week (water the plants and flush the rest down the drain) and then refill the pond with tap water.
This article also appeared in KoiWijzer and was provided by the Koi and Pond Advisory Group.
Text: René Grootscholten
Photos: René Grootscholten, Marco de la Penha
