General information about water plants

Pros and cons ...

Water plants look lovely and create a tranquil environment and compliment your pond.
They are expensive. The current price of a normal fairly small water Lily is currently R 50.00.
They preclude you from using too much salt in the water. With plants, you are limited to 0.1% (1,35 kg / 1000 l) salt concentration although the ideal concentration for Koi is 0.2% (2.7 kg / 1000 l)
Because you are limited with your salt concentration, you might have more algae growth, but on the other hand, your plants may use all the nutrients and leave none for the algae to grow.
They preclude you from treating the pond properly with certain chemicals.
They give hiding space for the fish which gives them better protection against sunlight, birds and other elements;
The big Koi tends to eat the plants. It is therefore sometimes needed to protect the plants from access by the fish. The ideal is to place your plants in your bio filter.
Proper care has to be taken to ensure that the plant is not poisonous to the fish;
If there are too many plants, you might not see the fish.
They can easily overgrow the pond and require constant attention if not controlled properly.
They help to eliminate Ammonia, Nitrites and especially Nitrates.
They might create a breeding ground for bad bacteria (Aerosomonas and Pseudomonas)
At night time they use oxygen and therefore compete with the fish if there is limited oxygen in the water.
They compete with and therefore control excessive algae growth because they use the Nutrients and Nitrates in the water also required by algae.
During day time they create oxygen which is beneficial to the fish.
They can introduce fatal bacteria or parasites if proper treatment has not been taken. They should always be placed in quarantine before introduced to the pond. (Potassium or Dipterex)
They provide spawning material in the spawning season. After spawning, the plants can be removed easily and placed in a spawning tank, thereby preventing the fish from eating the eggs.

In my post above I mentioned that all plants have to be treated with Potassium or Dipterex.

I recently introduced plants to one of my ponds, and eventhough I treated with Potassium, I had problems with leeches.

In view thereof, I will treat with Potassium AND Dipterex in future. The Potassium is very good for most parasites including snails but does not sort out leeches.

In addition to what I said above about the pros and cons, also bear the following in mind.

Although the plants use some of the Nitrates which is not good for the Koi, The Nitrates created by the Koi via Nitrites are much more than what plants can sort out. With 10% water changes, you get a far better result.

Remember that Koi loves a strong current. Plants don't

Plants need shallow water, koi needs deeper water.

Plants like nutrients, koi need to be protected against too many nutrients.

Plants like carbon dioxide and neutral to acidic water conditions, koi like neutral to slightly alkaline systems and low carbon dioxide.