Empty and inspect the tank first

Before you add water or anything else, remove any loose debris, algae buildup, or sediment from the glass and surfaces. Use a dry cloth or soft brush to wipe down the inside walls. If the tank has been sitting unused, you may find dust, dead algae, or mineral deposits that come off easily when dry.

Check the glass carefully for cracks or clouding. Hold it up to light and look at seams and corners where damage often starts. If you find cracks, the tank is not safe to refill — water pressure will make them worse. Clouding from mineral deposits can sometimes be cleaned, but permanent etching in the glass cannot be reversed.

Key Takeaways

  • Remove loose debris and algae with a dry cloth first, then rinse thoroughly with tap water and a soft brush or sponge.
  • Never use soap, bleach, or chemical cleaners inside the tank — they leave residue that harms fish and are difficult to rinse completely.
  • For stubborn algae and mineral deposits, white vinegar or a plastic scraper works safely without chemicals.
  • Rinse the tank at least three times with fresh tap water after cleaning to remove all debris and cleaning solution.
  • Let the tank air-dry completely or dry it with a clean cloth before adding substrate, decorations, or water.

Scrub with water and a soft brush or sponge

Fill the tank with tap water and let it sit for 10 to 15 minutes to soften any stuck-on algae or mineral buildup. Use a soft-bristled brush, sponge, or non-abrasive scrubbing pad to work around the inside surfaces. Avoid steel wool or hard plastic scrapers on acrylic tanks — they scratch easily. Glass tanks can handle a plastic scraper, but go gently on the seams.

Pay special attention to corners and the bottom, where debris collects. Drain the water and repeat the scrub-and-rinse cycle until the water runs clear. This usually takes two to three rounds. Do not rush this step — leftover debris or algae spores can cloud the water or cause problems once fish are added.

Use vinegar for stubborn deposits

White vinegar is safe for aquariums and works well on mineral deposits and old algae stains. Mix equal parts white vinegar and tap water in the tank, or spray it directly on problem areas. Let it sit for 15 to 30 minutes, then scrub gently with a soft brush. The acidity breaks down mineral buildup without leaving toxic residue.

Rinse thoroughly after using vinegar — at least twice with fresh tap water. Any vinegar smell should fade completely. If the smell lingers after rinsing, drain and rinse again. Vinegar is harmless to fish in tiny amounts, but you want the tank clean, not scented.

Never use soap or bleach

Soap, dish detergent, and bleach are toxic to fish and difficult to rinse completely from porous surfaces like silicone sealant. Even small amounts left behind can poison the water. If you have already used these products, drain the tank completely and rinse it at least five times with fresh water, letting it air-dry between rinses.

The same rule applies to commercial aquarium cleaners — read the label carefully. Many are safe for use in an empty tank but must be rinsed out before water and fish are added. If you are unsure whether a product is safe, stick to water, vinegar, and a brush.

Clean the glass from the outside

Once the inside is clean and dry, wipe the outside glass with a damp cloth or glass cleaner. Standard window cleaners are fine for the outside — they do not touch the water or fish. Wipe the frame and any plastic trim with a separate damp cloth to remove dust and old algae residue.

If the outside glass is cloudy or has hard water stains, white vinegar works here too. Spray it on, let it sit for a few minutes, and wipe clean. Dry the outside with a lint-free cloth to prevent streaks.

Rinse the substrate and decorations

If you are reusing gravel, sand, or other substrate from the old tank, rinse it thoroughly in a bucket with tap water. Stir it and drain several times until the water runs clear. This removes algae, fish waste, and debris that settled in the substrate. Do the same for any rocks, plants, or decorations you plan to reuse.

New substrate does not need rinsing unless the bag says it does — most modern aquarium gravel is pre-washed. Decorations from other sources should be rinsed and inspected for cracks or sharp edges before going into the tank.

Let everything dry completely

After rinsing, let the tank air-dry for at least a few hours, or wipe it dry with a clean, lint-free cloth. Moisture left inside can promote algae growth before you even add fish. If you are in a hurry, use a cloth — it is faster and ensures no water spots remain.

Substrate and decorations can dry while you wait, or you can add them damp — that does not matter. What matters is that the glass and seams are dry before you fill the tank with water for the first time.

Frequently Asked Questions

Can I use a magic eraser on aquarium glass?

Magic erasers are melamine foam and shed tiny particles that can cloud water or harm fish. Avoid them inside the tank. For the outside glass, a magic eraser is safe, but rinse the glass afterward to remove any residue before it touches the water.

What if the tank smells bad after cleaning?

Smell usually means bacteria or mold is still present. Drain the tank, rinse it again with vinegar and water, and let it air-dry in sunlight if possible — UV light kills bacteria and mold. If the smell persists after a second cleaning and drying, the tank may have damage or contamination inside the seams that cannot be reached.

Do I need to cycle the tank after cleaning an old one?

Yes. Cleaning removes the old bacteria colony that kept the tank stable. A clean tank is essentially a new tank and needs to cycle for two to four weeks before fish are added, or you can use a bacterial starter product to speed the process. The age of the tank does not matter — the cycle is about establishing bacteria in the filter and substrate.

Is it safe to use the old filter from a dirty tank?

The filter media (sponge, cartridge, or floss) can be rinsed gently in old tank water or tap water to remove debris, but do not scrub it hard or replace it yet. The bacteria living in the filter are what you want to keep. If the filter housing is visibly dirty, rinse it separately, then reassemble with the original media.

How long should I wait before adding fish after cleaning?

Wait at least 24 hours after the final rinse and drying. This gives any remaining vinegar smell time to fade and lets the water settle. If you are cycling the tank from scratch, wait two to four weeks before adding fish, depending on whether you use a bacterial starter.