Your koi may not be able to talk (unless you’ve been standing in the sun way too long), but they constantly “tell” you how they’re doing. A quick daily health check is like a mini vet visit you can do in just a few minutes—with no stethoscopes, no drama, and no koi co-pays.
The best part? You don’t need special tools or a lab coat. Just your eyes, a little observation, and maybe a cup of coffee while you stare lovingly at your living jewels.
Let’s walk through a simple step-by-step health check you can do any day, in any pond, to catch problems early and keep your koi thriving.
Step 1: Start With the Big Picture (Pond Check)
Before you zoom in on your koi, take a moment to look at their world. If the pond is struggling, the fish will be next.
- Is the water clear? Slight green or tea color can be normal, but cloudy, milky, or murky water is a warning sign.
- Any strange smells? A healthy pond shouldn’t smell like a swamp or a chemistry experiment.
- Equipment running? Check that pumps, filters, waterfalls, and air stones are all functioning and moving water well.
- Any foam or scum on the surface? A little from feeding is okay; lots of persistent foam can mean water quality issues.
Quick rule: happy pond = happy koi. Always start with the environment.
Step 2: Roll Call – Is Everyone Present and Swimming?
Now, look at your koi as a group.
- Are they all visible?
- Anyone isolating in a corner or hiding at the bottom?
- Are they swimming smoothly and calmly?
Healthy koi move with purpose and grace. They don’t crash into things, wobble sideways, or freeze like plastic decorations.
Red flags at a glance:
- One koi off on its own.
- Fish hanging near the surface, gulping.
- Fish glued to the bottom, not moving much.
Step 3: The Feeding Test (Your Built-In Diagnostic Tool)
Feeding time is more than fun—it’s your best daily health check.
As you toss in food, watch:
- Do they rush to the food? Healthy koi act like you’re serving an all-you-can-eat buffet.
- Is anyone slow or uninterested? A koi that doesn’t eat has something wrong—even if it still looks okay.
- Any awkward chewing or spitting? Could point to mouth problems, gill issues, or parasites.
Pro tip: A koi that skips one meal once might just be moody. A koi that skips multiple meals in a row is sending up a red flare.
Step 4: Body Scan From Above
While they’re at the surface eating, this is your moment to visually inspect each fish. No nets, no stress—just a good look from the top.
Check the following:
- Body shape: Smooth, symmetrical, no sudden lumps or dents.
- Scales: Lying flat and even, no raised “pinecone” effect.
- Color: Bright and even. Watch for sudden fading, grey patches, or unusual spots.
- Skin: No ulcers, red sores, cotton-like growths, or strange films.
Don’t worry about small pattern changes over time—that’s normal. Worry about fast, obvious changes.
Step 5: Fins, Tail, and Slime Coat Check
The fins and tail are like the koi’s flags—they show health before the rest of the body does.
- Fins: Should be spread, not clamped. Look for fraying, tears, or red streaks.
- Tail: Full and smooth, not ragged or eroded.
- Slime coat: Fish should look glossy, not dusty or covered in milky slime.
Signs of trouble:
- Clamped fins (fins held tight against the body).
- Red veins radiating through fins.
- Thick milky coating or “fuzzy” patches.
Step 6: Watch Their Breathing
Breathing tells you a lot—especially about gills, oxygen levels, and stress.
- Gills should move steadily and smoothly.
- Koi should not be panting or heaving.
- They shouldn’t need to hang out at the surface to breathe.
Warning signs:
- Rapid gill movement even when resting.
- Gasping at the surface or near waterfalls.
- Only one gill cover moving, or one held tightly shut.
If breathing looks off, test your water immediately—oxygen, ammonia, and nitrite are often the culprits.
Step 7: Behavior Check – Acting Weird or Normal Weird?
Koi have personality. Some are bold, some shy, some are drama queens. You’ll get to know what “normal” looks like for your fish.
But in general, healthy koi:
- Swim with the group.
- Respond when you approach.
- Don’t crash, spin, or repeatedly scratch.
Behavioral red flags:
- Flashing: Rubbing quickly against walls or rocks.
- Darting: Sudden, panicked bursts of speed.
- Spiraling or rolling: Serious sign something is very wrong.
- Extreme jumpiness: Frequent jumping or leaping out of the water.
Any of those behaviors = time to investigate water quality and possibly parasites.
Step 8: Quick Water Check (Your Invisible Health Factor)
Your koi live in their drinking water, bathroom, and atmosphere—all at once. So even the best-looking fish will suffer if the water is off.
A “simple health check” should always include regular testing (even if not every single day):
- Ammonia: 0 ppm
- Nitrite: 0 ppm
- Nitrate: Ideally under 40 ppm
- pH: Stable, no big daily swings
- Temperature: Consistent, not swinging wildly
Pro tip: When in doubt—test. Most health problems start with water, not the fish.
Step 9: Hands-On Check (Occasional, Not Daily)
For a truly thorough health check, advanced keepers sometimes net a koi for close inspection. This isn’t needed every day—in fact, too much handling causes stress. But occasionally, especially if you suspect a problem, it’s useful.
When you do:
- Use a soft, koi-safe net and a koi sock if possible.
- Wet your hands before touching the fish to protect the slime coat.
- Check gills (they should be a healthy pink, not pale or brownish).
- Look closely at the underside where you normally can’t see.
If you’re not comfortable handling koi yet, don’t worry—top-down checks and good observation go a long way.
Step 10: Trust Your Gut (You Know Your Pond Best)
Here’s the secret nobody tells beginners: as you spend time with your koi, you’ll develop a “pond sense.” You’ll just feel when something isn’t quite right—maybe they’re less active, slower to feed, or the pond looks different.
Listen to that feeling.
- Re-check your basics.
- Test the water.
- Watch a little longer.
- Take notes if needed.
Your koi’s best defense is a keeper who pays attention.
A simple koi health check doesn’t require fancy gear or hours of effort. In just a few minutes, you can look at the pond, count heads, watch them eat, scan their bodies, and observe their behavior.
Watch often, test regularly, and investigate early. The more you see your koi on their “good days,” the faster you’ll notice a bad one—and that early catch can make all the difference.
Plus, let’s be honest: “I have to go check on my koi” is one of the best excuses to sit outside, relax, and enjoy your pond every single day.