If you keep fish in your water garden, you probably use a pump with a filter to keep the water clean. Sometimes we tend to forget that filtering the water is not enough to maintain a healthy environment for fish. All a filter does is to collect solid debris and concentrate it in the filter media. But the debris is still there, contaminating the water in one form or another, until you clean the media of debris. Remember: What goes into your pond stays in your pond until you remove it.
Dry fish food? It's there. Oh, it will have changed from fish food to fish feces, but the waste matter is still there. Chemical additives? They're there. Salt? Medications? Fallen leaves? Still there. While you can remove some of those waste products by back-flushing or cleaning out your filters, you're going to need to do more. You're going to need to be diligent about making periodic partial water changes.
Remember, filters arenít perfect. They donít remove liquid chemicals such as ammonia or tiny contaminants held in suspension. Only partial water changes reduce toxins from the water through the process of dilution. A good rule of thumb is to provide a ten percent water change each week for fishponds and once a month for non-fishponds. (Yes, water plants can fall victim to toxic waste, too!)
What about a naturally occurring pond? Who changes the water there? I thought you'd never ask.
In a natural pond, the water is constantly being replaced. Every time it rains or a stream overflows its banks or somebody leaves the sprinklers on too long, the water makes its way downhill and eventually ends up in some creek, stream, or pond.
Similarly, the number of fish and other water creatures a natural pond can support was established eons ago by nature. That's not the case with man-made ponds. Of course, we could build ponds and stock them in the same ratio as nature intended...say, one fish for every 500 gallons of water. But that wouldn't be much fun. That's where partial water changes come in.
Theyíre simple to make, too. Just take your garden hose, remove the nozzle, and place the business end of the hose in your pond. Then turn on the water until the hose is full and the water runs out the end.
Next, turn the water off (keeping the hose end submerged), disconnect the opposite end of the hose from the spigot, and carry it to a place lower in elevation than the end thatís suspended in the pond. The water will start flowing through the hose, seeking out the lowest point and acting as a siphon.
Once you have removed approximately ten percent of the water, reverse the process, replacing what you removed.
The results will be a healthier water environment for all your living things, including plants. You can count on it!