Should You Keep Your Filter On or Off During a Water Change?

If you’re a fishkeeping beginner, you’ve probably had the age-old question pop into your mind — should you leave your filter on or off during a water change? The truth is, there’s no one-size-fits-all answer. It depends on how much water you’re changing and a few other factors. 

But don’t worry — we’ll break it all down so you can confidently tackle your next water change without stressing out. Let’s dive in!

The Filter’s Role

Your filter helps maintain a healthy environment, tirelessly circulating water, adding oxygen through surface agitation, and keeping beneficial bacteria alive. But when it comes to water changes, its role gets a bit tricky. So, when should you put your filter on or off? Let’s chat on how you can keep everything running (or not) smoothly.

Not in for reading? Feel free to watch our video to follow along:

Why You Should Keep Your Filter ON

For small water changes (10-20%), it’s best to keep your filter running. Here’s why:

• The water level stays above the filter intake: This means your filter can continue operating as normal without losing its siphon.
• Maintains oxygen supply: The surface agitation from your filter helps oxygenate the water, which is crucial for your fish.
• No need to mess with your filter: Keeping it on avoids unnecessary adjustments.

But here’s a pro tip: If you’re removing just enough water to expose the filter intake, turn it off right before the water level drops below it. Letting the intake run dry can break the siphon inside your filter hoses, leading to a frustrating re-priming process.

Why You Should Keep Your Filter OFF

For larger water changes (50-80%), it’s safer to turn off your filter. Here’s why:

• Prevents siphon breaks: When the water level drops below the filter intake, the siphon can break, which may result in your filter pumping gunky water back into the tank during restart.
• Avoids motor strain: Running a filter with the intake valve closed or no water can damage the motor. Unplugging it is a safer option.

What Is a Siphon Break?

A siphon break happens when air enters your filter hoses and disrupts the flow of water. This can make restarting your filter a messy ordeal, with trapped gunk releasing back into your tank — right after you’ve cleaned it! 

How to Avoid a Siphon Break

If your water change will drop the level below the filter intake, follow these steps:

1. Close the intake valve: Before the water level drops, close the valve to stop water flow into the filter.
2. Unplug the filter: If refilling will take a while, turn off the filter to prevent motor strain.
3. Refill the tank: Once the water level rises above the filter intake, open the intake valve to restore flow.
4. Restart your filter: Open the valve first to let water fill the filter and hoses (you’ll hear some gurgling). Once the sounds stop, plug the filter back in to restart it — no dirt cloud, no hassle!

Ready to Simplify Your Fishkeeping? Aquabuildr Is Here to Help!

Feeling overwhelmed by water changes or fishkeeping in general? Explore Aquabuildr, our fishkeeping app that simplifies aquarium care for beginners and experienced hobbyists alike. With its intelligent algorithm and user-friendly features, Aquabuildr helps you:

• Create custom tanks with accurate pH, temperature, and fish compatibility suggestions.
• Monitor your tank with intelligent alerts for water changes, fish compatibility, and more.
• Choose from various starter tanks or design one from scratch.

Aquabuildr is designed to take the guesswork out of fishkeeping, so you can focus on enjoying your aquarium. Get started for FREE on the App Store or Google Play Store, and start building your dream aquarium! 

Happy fishkeeping!