Why is My Fish Tank Cloudy? How to Clean an Aquarium

You bought a nice aquarium, filled it with all the right decorations, set up the filter, and added your favorite fish.

So why is my fish tank cloudy?

If your tank walls are starting to look a little hazy, it’s time to clean your tank. We’ve put together this guide to walk you through the process (and don’t worry—it’s easier than it seems).

Keep reading to learn what to do first!

Do You Need to Take the Fish out First?


You won’t be removing all the water from your tank when you clean it, so your fish will be perfectly safe swimming in the tank during the process. Trying to catch them all can take a lot of time and often ends up being more trouble than it’s worth.

How to Clean Your Aquarium

Before you start cleaning your aquarium, make sure you have an algae scraper and a siphon on hand. If you don’t have them already, you should be able to buy them at your local pet store.

Scrub the Walls

Start by reaching into your tank and scrubbing down the insides of the walls with an algae scraper. This will prevent anything from growing on the walls and clouding your view.

Wash Any Decorations

Next, remove any decorations, rocks, shells, etc. if you can. Large rocks or growing plants that are secured to the bottom can stay where they are.

Wash these decorations off in the sink or a bucket of water, but don’t use any soap or detergent. It’s difficult to remove all the soap from the surface, and it can be harmful to your fish if even tiny amounts get into your aquarium. Instead, stick with the algae scraper.

It should remove the debris just fine.

You can also take this moment to trim any plants growing in your aquarium. Pruning them will keep them from growing too large and taking up too much space.

Turn off Any Equipment

Things like the filter or the heater aren’t designed to run without water, so turn them off before you move to the next step. Otherwise, you could end up damaging them.

Vacuum the Substrate

Use your siphon to vacuum the substrate at the bottom of your tank. This will remove any debris, pick up bacteria, and reduce aquarium food waste.

Keep in mind, you’ll be sucking out water as you do this, so you’ll want to move fast. Keep going until you’ve gone over all your substrate and until you’ve removed about 3/4ths of the tank’s water.

Refill the Tank

Now you’re ready to put the decorations back inside the tank and refill it with clean water, I encourage you to buy distilled water.

Make sure the water you use is unchlorinated and the same temperature as the rest of the water in your tank. You may need to condition the water first to ensure it’s safe for your fish.

Turn Equipment Back On

Turn your equipment back on and let it run for a few hours. The water in your tank might be cloudy right after cleaning, but as the substrate settles and the filter gets to work, it will clean up.

Why Is My Fish Tank Cloudy? A Sign It’s Time to Clean

If you’re asking yourself, “Why is my fish tank cloudy?”, it’s probably time to give it a clean. Make sure you follow this guide to get rid of all the algae and debris and to keep your fish safe and healthy at the same time.

Want to learn some other helpful tips for first-time fish parents?

Make sure you take a look at the rest of our blog!

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