Pond water changes color over time, and brown or the tea-colored sort is among the most common pigments most koi pond owners will notice. Thankfully, this pigmentation can still be treated as long as you know the root cause of the problem and how to go about solving it.
The Root Cause
One key instance that causes water to turn brown or become tea-colored is the building up of tannins in it. A tannin is a form of a molecule that comes from specific species of plants. When plants break down and their leaves fall into the pond, they release tannins that apply such a glow to the water as a result.
First, remove excess plant material from the water surface. These unwanted elements are comprised of leaves and sticks, so get rid of them as much as possible. Additionally, any leaves and sticks around the edges of the water could also affect water coloration, so dispose of them properly.
Second, inspect the bottom part of your pond. This step is sometimes overlooked, thus making the water still appear tea-colored. Once you have confirmed that the bottom of the pond is still packed with sufficient tannin-producing components, remove that stuck vegetation debris slowly but thoroughly.
Third, doing a fractional water change is a good idea as this process can help, too. If you want the tannins to break down over time with minimal effort, consider having bacteria and algae in your pond. For the fastest and least hassle way of tannin removal, think about adding activated carbon to your pond, which will stick with the tannins and take them out of the water.