Why Regular Water Changes Matter in Your Koi Pond

By Tri-Star Koi

If there’s one habit that separates good koi keepers from great ones, it’s regular water changes. It might not be the most exciting part of koi keeping, but it’s easily one of the most important. At Tri-Star Koi, water changes are a non-negotiable part of our care routine—and for good reason. We change our water everyday for our koi, and they appreciate it.

No filter, no chemical, no UV system can replace the benefits of simply removing old water and replacing it with clean, fresh water. It’s the foundation of a healthy pond, and your koi will show the results.

What Do Water Changes Actually Do?

A water change isn’t just about topping off for evaporation—you're removing waste, toxins, hormones, and balancing out what filtration alone can't handle. Here’s what a proper water change helps with:

• Dilutes harmful substances like ammonia, nitrites, nitrates, and organic waste buildup

• Removes dissolved solids that accumulate over time and aren't removed by filters

• Replenishes essential minerals that koi need for strong immune systems and proper growth

• Stabilizes pH and KH by replacing buffering agents lost over time

• Improves oxygen content, especially in warmer months when oxygen demand increases

• Refreshes the pond environment, reducing stress and helping koi thrive

How Often Should You Change the Water?

At Tri-Star Koi, we recommend starting with a 10%–20% water change weekly. This is a safe, effective baseline for most hobbyists with established ponds. However, frequency and volume can vary depending on:

• Stocking levels

• Feeding rates

• Filter size and performance

• Season and temperature

• Overall water quality

In warmer months or in heavily stocked ponds, more frequent changes (even up to 30% weekly) may be needed. In cooler months, you may scale back to every other week—just never stop completely.

Do You Need to Dechlorinate?

If you’re on city water, yes—always use a water conditioner to remove chlorine and chloramines. These chemicals are toxic to koi and can damage their gills or even cause sudden death.

If you’re using well water, make sure to test for iron, pH, and temperature before adding it directly. Just because it’s “natural” doesn’t mean it’s safe without testing.

What Happens If You Don’t Change Water Regularly?

Over time, a neglected pond becomes what we call "old water"—it may look fine, but it’s chemically imbalanced, low in oxygen, high in waste, and harmful in the long run. Here’s what that can lead to:

• Sluggish koi or poor appetite

• Increased parasite and bacterial outbreaks

• Stunted growth due to poor water quality

• pH crashes that can shock or kill koi

• Ulcerations or fin rot caused by excess organic load

Even the best filter system can’t remove every trace of waste or restore minerals—that’s your job, and it starts with water changes.

How to Do a Proper Water Change

Here’s a simple routine you can follow:

1. Turn off the pump and aeration (if needed)

2. Drain 10–20% of the pond water using a bottom drain or pump

3. Vacuum or rinse filters if it’s part of your schedule

4. Slowly refill with fresh water, ideally close to the pond's temperature

5. Add dechlorinator if using tap water

6. Turn everything back on and observe your koi for any changes

You’ll often notice your koi more active, more vibrant, and more eager to feed after a good water change. That’s your proof it’s working.

If you want your koi to thrive—not just survive—clean, fresh water is non-negotiable. Regular water changes are the simplest and most powerful way to prevent illness, promote growth, and give your koi the environment they need to stay strong.

At Tri-Star Koi, we see water changes as pond maintenance 101. They don’t take long, they aren’t complicated, and they pay off big.

— Marlon @ Tri-Star Koi