Pond Maintenance

How Do I Prep a Koi Pond for Summer?

One week you’re still wearing a jacket, and the next your pond thermometer is reading 75°F and your koi are acting restless. Koi pond maintenance in Union County, and really anywhere in northern NJ, is all about getting ahead of the heat before it creates problems.

Here’s what we’d walk through with any pond owner before summer kicks in.

Key Takeaways

• Koi feeding, metabolism, and oxygen needs all change once your water temperature gets over 60°F, timing your prep to that threshold matters more than the date on the calendar.
• Summer heat depletes dissolved oxygen faster than most pond owners expect; sorting out aeration early is one of the highest-impact things you can do.
• Catching water quality and equipment issues in May is a lot easier (and cheaper) than dealing with stressed fish or an algae takeover in July.

1. Test Your Water First!

Before you do anything else, you need to get a baseline reading on your water chemistry.

What To Test For

• PH: your target should be around 7.0–8.0
• Ammonia and nitrite: both should read zero
• Nitrate: aim to keep it below 40 ppm
• Dissolved oxygen: helpful if you have the kit for it

If something’s off, fix the water first. Remember: Rapid corrections stress fish just as much as the problem itself. So make water changes deliberately and by degree.

2. Clean Out Debris

Any leftover leaves and debris will break down through summer, driving ammonia levels up while pulling oxygen out of the water.

Quick Cleaning Tips

• Skim the surface and use a net or pond vacuum on the bottom
• Do a partial water change (10 to 20 percent) if there’s heavy sludge buildup
• Treat fresh water with a detoxifier before adding it to the pond

3. Check Pumps and Filters

Pay attention when you run your pond pump. If you notice reduced flow, strange noises, or any visible cracking in the tubing, it’s a good idea to have a pro come out and take a look.

Tips for Filter Cleaning

• Use pond water to clean the filter, NOT tap water — tap water kills beneficial bacteria that your filter depends on
• Replace worn or permanently clogged filter pads now
• Check all plumbing connections for slow leaks while everything is accessible

4. Rebuild Your Beneficial Bacteria

Biological filtration slows way down over winter and will need time to rebuild.

Add a dose of beneficial bacteria now, and plan to dose again after:

• Heavy rain events
• Partial water changes
• Any antibiotic treatments

It’s cheap insurance for water clarity and fish health through the whole season.

5. Seriously Think About Aeration

This is probably the most underestimated part of summer pond prep. Dissolved oxygen drops as water temperature rises — and in a Union County summer, pond temps can easily climb into the mid-80s. Koi need well-oxygenated water to stay healthy and active.

Aeration Red Flags

• Koi consistently hovering near waterfalls
• Fish near the surface, especially in the morning
• Sluggish behavior on hot days

If you’re relying on a single waterfall for pond aeration, consider adding a dedicated air pump or diffuser. It’s a lot easier to add one in May than to troubleshoot oxygen stress in August.

6. Adjust Your Koi Feeding Schedule

Koi fish metabolism is driven almost entirely by water temperature, and in summer it starts to ramp up.

Koi Feeding Schedule

• Below 50°F: Stop feeding entirely
• 50–60°F: Feed once daily with wheat-germ-based spring food
• Above 60°F: Transition to higher-protein summer food, up to 2–3 feedings per day
• Above 90°F: Scale back, heat stress can suppress digestion

Pro Tip: Feed only what your fish can finish in about 5 minutes. Any more will be wasted and any less will leave your fish hungry.

7. Check Your Plant Coverage

Aquatic plants consume nutrients that would otherwise feed algae, provide shade that moderates water temperature, and give koi places to feel secure.

A few practical guidelines:

• Aim for 40 to 60 percent surface coverage
• Water lilies and lotus both do well in New Jersey ponds through summer
• Late spring is the right window to add plants — before the heat peaks and algae gets a head start

If your pond is light on coverage, now is the time to fix that.

8. Check for Predator Vulnerabilities

Great blue herons are patient and persistent. They’ll work a koi pond methodically, and summer is prime hunting season.

What to look for:

• Pond areas shallower than 2 feet — koi need depth to retreat
• Open sight lines with no overhead cover or plant structure
• Any spots along the edge where a heron can stand comfortably

Motion-activated deterrents, pond netting, or added rock structures can all help. Shallower ponds in open yards are the most at risk.

9. Do a Slow Visual Check on Your Fish

Take 10 minutes and inspect each fish. Koi can sometimes carry parasites or low-grade infections that flare up with warming water.

Fish Red Flags

• Red streaks, white spots, or sores on the body
• Torn or clamped fins
• Unusual swimming posture or erratic movement
• Lethargy or loss of appetite

A lot of symptoms that look like disease are actually water chemistry problems in disguise. If water tests clean and fish still seem off, get a professional set of eyes on it sooner rather than later.

10. Book a Professional Cleaning if You Need One

If your pond didn’t get a proper spring cleaning (or if it’s been more than a year since a thorough service) don’t push it into summer. A professional cleaning removes accumulated sludge, restores your pond’s biological balance, and gives you a clear read on equipment health before the most demanding season of the year.

Get a Professional Pond Inspection from Atlantis Water Gardens!

If you want a second set of eyes on your pond before summer hits, or you need a spring cleaning, water quality check, or some help figuring out what’s going on with your fish, Atlantis Water Gardens is happy to help!

We’ve been building and maintaining koi ponds in New Jersey for over 20 years and we can help keep your pond and fish happy and healthy all year long.

📞Call: 973-627-0515

🌐 Contact Us Online

FAQs: Summer Koi Pond Maintenance

When should I start feeding my koi again after winter?

Go by the temperature, not by a date. When your water temps are consistently above 50°F, start feeding a wheat-germ-based spring food. Wait on feeding higher protein food until the water is reliably above 60°F and your fish are actively feeding.

How do I know if my pond has enough oxygen for summer?

Keep an eye on your fish. If they’re constantly near the waterfall, sitting at the surface in the morning, or looking lethargic, they’re probably dealing with low dissolved oxygen. Adding an air diffuser or secondary aerator is usually the quickest fix.

How often should I change the water in summer?

A basic rule for this is to do a 10-15 percent partial water change every 2-4 weeks. Make sure to test your water and if ammonia or nitrate levels are creeping up, increase change frequency. Don’t forget to treat your water with detoxifier before putting it in your pond.