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Fish Tank Cloudy? What White, Green or Brown Water Is Telling You

The color of the haze points to the cause. Feed less, change a quarter of the water and wait a few days. A clarifier helps the haze that stays.

By Jamilur Rahman Updated November 5, 2026 · 6 min read

Time
30 min, then a few days
Cost
Under $20
Difficulty
Easy
A home aquarium filled with milky cloudy water, with small fish and plants faintly visible
In this guide
  1. Quick answer
  2. Free vs. permanent fix
  3. What you'll need
  4. Why it happens
  5. Try this first (free)
  6. When free fixes aren't enough
  7. Buy the fix
  8. Fish tank not clear or not clearing up? Check these four things
  9. What to skip
  10. FAQ
  11. Related problems

Quick answer

Why is my fish tank cloudy? The color of the haze tells you the cause. White or milky water is usually a bacterial bloom from overfeeding or a new tank, green is algae from too much light, and brown is usually diatoms or driftwood tannins. Feed less, change a quarter of the water, rinse the filter media in old tank water and give it a few days. A water clarifier can clump fine haze so the filter catches it.

Free fix vs. permanent fix

Free fix · 30 minutes, then 3 to 7 days

Feed less, change 25 percent of the water and wait

  • Skip a feeding, then feed only what fish eat in 2 minutes
  • Change 25 percent of the water with treated water
  • Vacuum part of the gravel, not all of it
  • Do not replace the filter media or scrub the whole tank

How long it lasts: Fixes most cloudy water. A bloom in a new tank usually clears by itself in about a week.

Most readers choose Permanent fix
Aquarium water clarifier (illustration)
Illustration

An aquarium water clarifier

A clarifier binds tiny floating particles into clumps your filter can catch. It helps with haze that does not clear after a week of the free fixes. It does not remove the cause, so keep up lighter feeding and regular water changes.

What to get: Aquarium water clarifier

How long it lasts: Works in a day or two on stubborn haze. The cause still has to be fixed or the haze returns.

Check price on Amazon

As an Amazon Associate I earn from qualifying purchases.

What you'll need

  • Clean bucket

    Use it only for the tank, never with soap

    You have it
  • Gravel vacuum with siphon (illustration)
    Illustration

    Gravel vacuum with siphon

    Pulls waste out of the gravel as it drains water

    Check price
  • Aquarium water conditioner (illustration)
    Illustration

    Aquarium water conditioner

    Needed for every water change

    Check price
  • Liquid test kit (illustration)
    Illustration

    Liquid test kit

    Shows ammonia, nitrite and nitrate, so you know the real cause

    Check price
  • Our pick
    Aquarium water clarifier (illustration)
    Illustration

    Aquarium water clarifier

    For haze that stays after a week

    Check price

Why it happens

1

White or milky: a bacterial bloom

It happens in new tanks, or after overfeeding. Bacteria multiply fast on extra food and waste. Fish are usually fine, and it clears on its own in days to a couple of weeks.

2

Green: an algae bloom

Too much light, such as direct sun or a lamp left on all day, plus extra nutrients from food and waste, feed free-floating algae.

3

Brown or yellow: diatoms or tannins

Diatoms are brown algae that often show up in new tanks and fade within weeks. Driftwood and some leaves tint the water tea-brown, which is harmless.

4

Gray or dusty: gravel dust

Gravel, sand and decorations that were not rinsed shed fine dust. It settles or filters out in a day or two.

5

A clogged filter or too many fish

A filter that is clogged or too small, or a tank with too many fish, lets waste build up faster than it clears.

Try this first (free)

Do these in order, starting with the simplest.

  1. Stop feeding for a day, then feed less

    Skip one feeding. After that, give only what your fish eat in about 2 minutes, once or twice a day, and scoop out leftovers.

  2. Test the water

    Tool used: Liquid test kit

    Test ammonia and nitrite. Both should read zero. If either is above zero, or fish are gasping at the surface, do a larger water change right away.

    Liquid test kit (illustration)
    Illustration

    Tool for this step

    Liquid test kit · Shows ammonia, nitrite and nitrate, so you know the real cause

    Check price on Amazon

  3. Change 25 percent of the water

    Tool used: Gravel vacuum with siphon

    Remove a quarter of the water and vacuum a third of the gravel. Refill with water at the same temperature, treated with conditioner. Do not change it all, because you would remove the good bacteria.

    Gravel vacuum with siphon (illustration)
    Illustration

    Tool for this step

    Gravel vacuum with siphon · Pulls waste out of the gravel as it drains water

    Check price on Amazon

  4. Rinse the filter media in old tank water

    Tool used: Clean bucket

    Squeeze the sponge or cartridge in the water you just removed, not under the tap. Chlorine kills the helpful bacteria. Never replace all the media at once.

  5. Cut the light

    Keep the tank out of direct sun and run the light 6 to 8 hours a day on a timer.

  6. Wait, then add a clarifier if haze remains

    Tool used: Aquarium water clarifier

    Give it 3 to 7 days. A new-tank bloom usually clears itself. If haze remains after a week of lighter feeding and a water change, add clarifier as the label says.

    Aquarium water clarifier (illustration)
    Illustration

    Tool for this step

    Aquarium water clarifier · For haze that stays after a week

    Check price on Amazon

When free fixes aren't enough

If the water is still cloudy after a week of lighter feeding, regular water changes and a rinsed filter, the haze is likely tiny particles too fine for the filter. A clarifier clumps them so the filter can trap them, and it often clears the tank in a day or two. If ammonia or nitrite is above zero, a clarifier will not help, so keep changing water until both read zero. If fish gasp at the surface or the water smells like rotten eggs, do a water change now.

Buy the fix

Still stuck after the free fixes? These are the products we would look at.

Our picks compared
PickProductFixesWho it's forBuy
Best pick
Aquarium water clarifier (illustration)
Illustration
Aquarium water clarifier
fine haze your filter cannot catch on its own Tanks that stay hazy after a week of the free fixes. Check price
Upgrade pick
Liquid freshwater test kit (illustration)
Illustration
Liquid freshwater test kit
guessing why the water keeps clouding up New tank owners and anyone whose tank keeps clouding. Check price
Best pick
Aquarium water clarifier (illustration)
Illustration

Aquarium water clarifier

Fixes: fine haze your filter cannot catch on its own

Look for: Labeled safe for freshwater fish, and for any shrimp or snails you keep; Clear dose instructions by tank size; Works alongside your filter, per the label.

Who it's for
Tanks that stay hazy after a week of the free fixes.
Honest downside
Ammonia or nitrite reads above zero, or the tank is brand new. Fix water quality first, and check the label if you keep shrimp.
Check price on Amazon
Upgrade pick
Liquid freshwater test kit (illustration)
Illustration

Liquid freshwater test kit

Fixes: guessing why the water keeps clouding up

Look for: Liquid tests for ammonia, nitrite and nitrate; A color chart that is easy to read; Enough tests for weekly checks.

Who it's for
New tank owners and anyone whose tank keeps clouding.
Honest downside
You already have a test kit. Check the expiry date first.
Check price on Amazon

As an Amazon Associate I earn from qualifying purchases. We don't show prices because they change, so use the button to see today's price.

How we picked: How we picked: this page is based on aquarium care guides, water-testing advice from fish keeping groups, and what owners report in reviews of clarifiers and test kits. We do not test products by hand.

Fish tank not clear or not clearing up? Check these four things

  • Feeding: are fish finishing all the food in 2 minutes?
  • Test results: are ammonia and nitrite at zero?
  • Filter: is it running, and is the media rinsed in old tank water?
  • Stocking and light: too many fish, or a lamp on all day, keeps water hazy.

What to skip

Changing all the water and swapping the filter

A full cleanout wipes out the helpful bacteria that keep your tank safe, and it can trigger an even bigger bloom. Skip big changes, and skip adding chemicals before you test the water.

Frequently asked questions

Why is my fish tank so cloudy right after setup?
A new tank has no stable bacteria yet, so a milky bloom is common. Stop overfeeding and wait, since it usually clears within a week or two.
Why is my fish tank water so cloudy even though I cleaned it?
Cleaning too hard can cause it. Replacing all the water or scrubbing the filter removes helpful bacteria, and the bloom follows. Do smaller, regular changes.
How do I fix fish tank cloudy water fast?
Feed less, change 25 percent of the water, rinse the filter media in old tank water, and add a clarifier if haze stays after a few days. Nothing works faster without risking your fish.
Why is my fish tank foggy right after a water change?
Fresh tap water can hold tiny air bubbles that look like fog and clear in minutes. Stirred-up gravel dust can also cloud it for a day. If it stays milky for days, look for a bloom.
Why does my fish tank look cloudy again, and how do I stop it from being cloudy?
If the haze returns after it clears, the cause is still there: too much food, too much light or a filter that needs care. Feed less, keep the light to 6 to 8 hours and keep up weekly water changes.

As an Amazon Associate I earn from qualifying purchases. Affiliate disclosure

Aquarium water clarifier (illustration)
Illustration

Our pick: Aquarium water clarifier

Check price