How to clean a fish tank
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How to clean a fish tank

No fish wants to swim in an algae filled, murky tank – and it won't do much for the ambience of your home, either. Find out how to clean a fish tank here!

Fish can be a great addition to the home – they’re easy to look after, therapeutic to observe, and kids adore them – but how do you make sure they stay healthy?

Keeping the tank clean is very important when it comes to keeping your fish alive and healthy, and you should be giving it a good clear out at least once every couple of weeks. Fortunately, if you forget to clean, you’ll have a very obvious reminder – see that green-tinted, murky water? That’s a sign that your tank is well overdue for a clean.

Before you start cleaning, however, you need to think about the kind of fish you have and their needs. When you purchased your fish, you should have been given some instructions on how regularly you need to clean, and how best to sort out your particular style of tank. Bear this information in mind as you use the guide below.

Why Should I Clean my Fish Tank?

Your fish need oxygen to breathe, but oxygen can be quite difficult to come by in a dirty fish tank. The more dirt and grime that’s floating around your fish tank, the less oxygen the water can hold. If your fish tank is filthy, it may be likely that your fish are struggling to survive.

Additionally, algae can form in dirty tanks. Now, algae itself isn’t hugely problematic (although it certainly doesn’t look pretty), but it’s when the algae starts to die off that things turn sour. Dying algae takes in a huge amount of oxygen, and in extreme cases it can actually remove all the oxygen from the tank.

As a guide, coldwater fish require around 6 mg oxygen per litre of water, and tropical fish slightly less, at 5 mg per litre. Cleaning your tank regularly – using the seven steps below as a guideline – is absolutely vital if you want to ensure your fish are happy and healthy.

Changing the Water in Your Fish Tank

If a friend asked you ‘How do I clean my fish tank?’ the first thing that would probably come to mind is changing the water – and you’d be right. However, changing all of the water at once can be hugely detrimental to the health of your fish. By rapidly changing their living conditions, you can trigger stress in your fish, which could make them ill, or even cause them to die. Your fish want a clean environment, but they also want a familiar environment. This is why, when you buy new fish, they’ll always be given to you in a small amount of their own water.

If you clean your tank regularly, you only need to change around 15 percent of the water at a time. This is just enough to give the tank a good refresh. If you’ve been a bit lax in cleaning your tank, aim to change about 25 percent. If you’re not sure, then check with a specialist.

  1. Change the water using a manual siphon, drawing the necessary amount of water out into a bucket.
  2. Dispose of the water and fill the bucket with the same amount of clean water that’s been brought up to the right temperature for the type of fish you own. Coldwater fish are happiest in temperatures of around 18 degrees Celsius, and tropical fish in temperatures of 25 degrees Celsius. If you’re not sure, then check with a specialist.

Always be sure to use a thermometer to reach the right water temperature, rather than trying to guess by feel. One aspect to keep in mind when changing the water is that the buckets you use should be clean and completely free from any soaps or detergents.

Removing Algae & Bacteria

Removing algae from your tank is easy: all you need is an algae pad, available in most pet shops.

  1. Use the algae pad to wipe off any algae from the inside of the tank.
  2. If any algae are tough and won’t wipe off, use a clean, stiff bristled brush to gently scrub it away from the glass.

Avoid using sharp instruments such as razor blades for this – they can scrape or scratch the glass, and they are particularly dangerous to use with acrylic fish tanks. You also shouldn’t use sharp objects if you’ve chosen not to remove your fish during the cleaning process, for obvious reasons.

To remove bacteria, you’ll need to focus on your gravel or sand, and your decorations.

  1. To clean bacteria from the gravel, hold your siphon hose about 1 centimetre above the surface of the gravel, gently running your fingers through the tiny stones – this is a two person job, so grab a friend to help you out. Moving the stones will disturb any old food flakes and dirt, allowing it to be sucked up by the siphon.
  2. To clean decorations, remove them from the tank and soak them in a tough cleaning solution. If you’ve got protective gloves and eyewear, you can use a mixture of warm water and Domestos Original Bleach – around 1 part bleach to 9 parts water. When using such a product ensure that the area is well ventilated and you follow the manufacturer’s instructions and safety guidelines. After soaking, rinse very thoroughly in hot water and return to the tank.

Cleaning the Glass

Once the inside of the tank has been thoroughly cleaned, you can begin to clean the outside of the glass. Of course, this has no effect on the health of your fish, but it does make it easier for you to enjoy watching your fish and monitor their living conditions. The best way to clean a fish tank from the outside is to use the same techniques you’d use when cleaning your windows or mirrors:

  1. Use a damp cloth dipped in white vinegar and wipe all across the glass, removing any sticky fingerprints and dust.
  2. Allow this to dry naturally, and then buff with a cloth to remove any streaks and watermarks.

You’ll have a sparkling clean tank in no time: a perfect home for healthy fish!

For more information on the ingredients in products mentioned in this tip, visit What’s in Unilever Products here.

Top Tip


You’ll find the full clean below much easier and more effective if you pay attention to all the other aspects of fish tank maintenance. Remember to clean the tank filter monthly, and try to tackle the algae on the glass (without draining the tank) about once a week.

Safety Warning


Use biocides safely. Always read the label and product information before use.