How to Use Activated Carbon in Your Aquarium

If you're keeping an aquarium and wondering how to keep the water clean, clear, and smell-free, then activated carbon might be your new best friend! But many beginners ask – what is activated carbon? how do I use it? and is it really worth it? 

What is Activated Carbon in Aquarium Hobby?

Activated carbon (also called activated charcoal) is a black, porous substance made from things like coconut shells or wood. It’s treated in a way that makes it super absorbent, meaning it can trap bad stuff from your aquarium water – things you can’t see, but that can harm your fish.

• It doesn’t remove fish poop or uneaten food (that's mechanical filtration’s job), but it absorbs chemicals, odors, medications, and yellow water.

Why Use Activated Carbon in Your Aquarium?

There are few big reasons hobbyists use it:

• Removes bad smell from the tank

• Clears yellow or cloudy water

• Removes leftover fish medications after treatment

• Helps fish feel less stressed in cleaner water

If your tank looks dull or smells odd even after water changes – carbon can fix it fast

Where to Put Activated Carbon in Your Aquarium?

Activated carbon needs to go inside your filter, where water flows through it.

🔹 For canister filters – Place it in one of the trays/layers.

🔹 For internal filters – Some models have a spot for carbon bags.

🔹 For hang-on-back filters (HOB) – Put it in a media bag or replace the carbon cartridge.

🔹 For sump filters – Use a mesh bag or a filter tray.

How Much Activated Carbon Should I Use?

Here’s a simple rule: Use about 1/2 cup of activated carbon per 189 litre of water.

But if your tank is heavily stocked or smells strong, you can use a bit more.

Also, always follow the instructions on the product label.

How Long Does Activated Carbon Last in a Tank?

Carbon doesn’t last forever! It usually becomes exhausted in 3-4 weeks, after which it stops absorbing stuff.

So, replace it every month or sooner if:

• Your water starts to smell again

• The water gets yellowish or cloudy

• After a medication cycle

Used carbon won’t harm your tank, but it won’t help either!

How to Use Activated Carbon (Step-by-Step)

1. Rinse the carbon in tap water (in a mesh bag) to remove black dust.

2. Place it inside your filter where water flows through it.

3. Let it run – you’ll see a difference in water clarity in 24–48 hrs!

4. Replace it monthly to keep the effect strong.

   
   

Pros & Cons of Using Activated Carbon

Pros:

• Clears water fast

• Removes smells and toxins

• Safe for fish & plants

Cons:

• Needs regular replacing

• Doesn’t remove ammonia or nitrites

• Can remove plant ferts if overused in planted tanks

If you have a planted tank, use carbon only when needed (like after meds or water discoloration).

Is Activated Carbon Necessary for Every Aquarium?

Not really. While it’s very helpful, it’s not always a must-have.

Good for:

• Community tanks

• Monster fish tanks (for odor control)

• After fish medication

Not required always for:

• Heavily planted tanks (use with caution)

• Tanks with natural tannins (like blackwater setups)

  
  

Activated carbon is like a magic sponge for your aquarium – it absorbs the bad stuff, leaves the good stuff, and keeps your water looking crystal clear!

If your tank is smelly, yellow, or just not looking fresh, try using activated carbon – it might be the game-changer your tank needs.