Stocking Fish and Plants

Introducing Fish and Plants to the Pond

Once the hard work of building a pond is complete, you begin the really fun part of pond ownership by stocking it with fish and plants. Simply put stocking comprises adding plants, fish and scavengers to your pond, in that order and in the proper proportions to achieve a balanced backyard pond.

Test the Water in the Fish Pond for Chlorine, PH and Ammonia

If your fish pond was filled with chlorinated water you should wait 3 days to a week for the chlorine to dissipate before adding any plants.  Aeration from waterfalls or fountains will speed the process up. There are inexpensive test kits that will test the water for chlorine. These kits also test for PH and nitrites which are also important for maintaining a healthy environment for both pond fish and plants.


Koi vs. Plants

Once the water is chlorine free you start adding aquatic plants.  Most koi and water gardening books that I have read caution about adding plants to koi ponds, due to pervasive foraging habits of koi uprooting  and/or eating the plants. Some books have even gone as far as recommending that a koi pond be kept plant free.  Plants add an lot in both appearance and functionality to backyard ponds through filtering, photosynthesis, delicate beauty, fragrance and providing cover and food for the fish. I must say that I have NEVER had a problem with including aquatic plants in my koi pond. As previously mentioned, I do have river rocks lining the bottom of my pond and when I add plants in pots (water lilies, iris and cannas) I use the same rocks to cover the soil. This protects the plants from the koi and also helps hold the soil in place.  With submerged plants such as anacharis, I just bury the roots in the river rocks on the bottom of the fish pond.


Location Matters

We live on the border of Zone 5 & 6 so some of the things I am going to mention in preparing the fish and plants for winter don’t apply in warm weather location.


Understanding the Nitrogen Cycle in a Fish Pond

One key to maintaining a healthy fish pond is establishing an environment that efficiently processes the nitrification cycle. When this is done naturally your water will be clear and your fish healthy with very little reliance on outside factors such chemicals, water changes and extraneous filters. The larger the pond relative to the fish load the easier it is to achieve this balance so it is critical to never overstock your pond with fish. In nature the fish population is not very dense, in backyard ponds, we will almost always want to have a higher concentration of fish per gallon of water. This can be sustained up to a certain level through the addition of mechanical and/or chemical systems for incremental filtration and aeration. However it is desirable from a cost, workload and safety point of view to keep their use to a minimum. Don’t exceed the stocking guidelines laid out on the “Pond Fish” page and allow the natural nitrogen cycle do its work. When you first set up your fish pond, the water is very clean with no bacteria or harmful chemicals, just clear, clean water you could drink.  After you allow any chlorine to dissipate the water is still relatively clean but then you add plants and eventually fish. Of course you will need to feed the fish which is when the potential problems can occur. Like all other creatures fish use what nutrients they need from the food and dispose of the rest as waste. When pond fish “go” , their waste decays in the water and turns into ammonia.  Also if the fish are fed more than they can eat the excess food decays and produces more ammonia which is toxic to fish.  So we need to use natural biological process to get rid of it.  Fortunately, the ammonia is food for certain types of “beneficial” bacteria,  As the ammonia level rises in the pond, these bacteria form, multiply and consume the ammonia. This is the first step in achieving a balanced nitrogen cycle in the pond . The fish population depending on numbers and size produce ammonia and the bacteria population needs to be big enough to consume it at the same rate. However as the “beneficial” bacteria consume the ammonia they give off a “waste” product of their own known as nitrite.  In effect they convert the ammonia into nitrite which unfortunately is also toxic to fish. However there is another strain of bacteria which consumes the nitrite and coverts it to nitrate which at low levels is not harmful. Again the population of this bacteria has to be in balance with the other organisms so the all the nitrite is converted to nitrate.  This is why we add pond fish gradually so the bacteria population can grow proportionately to the production of ammonia and nitrite by the fish. This is the second step in the nitrogen cycle in a fish pond. We can supplement the populations of “good” bacteria’s by circulating the water ( (preferably the total volume of the pond in one hour) through the bio-filter. This filter along with river rocks or gravel on the bottom of the pond or in plant pots provide additional surface area for the bacteria to multiply and achieve the balanced cycle. So we use beneficial bacteria to remove harmful ammonia and nitrite produced by fish wastes from the water. As the “harmless” nitrate accumulates, it will eventually get to a toxic level”. To keep the pond safe for your fish and reduce the chances of the water turning green due to excess algae growth , nitrates should be kept below 50 ppm. This can be achieved through frequent water changes, but the natural way to get rid of nitrates is by adding plants.  Plants consume nitrogen to grow (in this case in the form of nitrates) and a sufficient planting completes the cycle by removing nitrates from the water. Replacing water lost due to evaporation or rainfall overflowing the spillway also  naturally reduces nitrates.  So by achieving an appropriate balance between the fish and plant populations, building a biological filter and by making all changes gradually, a balanced nitrogen cycle can be set in place. This will result in a beautiful and healthy pond environment with a minimum of maintenance effort and cost.

NitrogenCycle edi Stocking Fish and Plants

Fish, Plants and Bacteria form the Nitrogen Cycle


Now you start building the nitrogen cycle by stocking Pond Plants

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