Rinse the tank and all equipment with water only

A brand-new aquarium comes with manufacturing dust, plastic residue, and sometimes protective coatings that need to come off before you add water and fish. Start by rinsing the empty glass tank itself with tap water and a soft cloth or sponge—no soap or chemicals. Wipe down the inside walls and the bottom, paying attention to corners where dust collects.

Rinse your filter, heater, air pump, and any decorations or plants the same way. If the filter came with a cartridge or media, rinse that too under running water. Do not use soap on any of these items; soap leaves a film that can harm fish and damage the filter's ability to work. A thorough rinse with plain water is all you need at this stage.

Key Takeaways

  • Rinse the tank, filter, heater, and all decorations with plain water only—no soap or chemicals.
  • Wash gravel or sand in a bucket under running water, stirring it several times, until the water runs clear.
  • Fill the tank with tap water, run the filter and heater for 24 hours, then test the water before adding fish.
  • If your tap water contains chlorine, let it sit for 24 hours or use a dechlorinator product before the fish go in.
  • A new tank needs 3 to 7 days of running empty to establish bacteria that keep the water safe for fish.

Wash gravel or sand until the water runs clear

Gravel and sand come packed with fine dust and sediment that will cloud your water if you skip this step. Place your gravel or sand in a large bucket—do not put it directly in the tank. Fill the bucket with tap water, stir the substrate vigorously for 30 seconds, then pour off the cloudy water. Repeat this process 4 to 6 times until the water you pour off runs clear or nearly clear.

This takes patience, but it makes a real difference in how quickly your tank becomes clear and how much work your filter has to do. Once the water runs clear, you can add the substrate to the tank. Spread it evenly across the bottom, sloping it slightly higher toward the back if you want a more natural look.

Fill the tank and run equipment for 24 hours before adding fish

Fill the tank with tap water to the level marked on the tank or to about an inch below the rim. Turn on the filter and heater and let them run continuously for a full 24 hours. This allows the heater to bring the water to the right temperature and gives the filter a chance to circulate water through the system before any fish are present.

During this 24-hour period, check that the heater is warming the water to the temperature your fish need—most tropical fish do well at 76 to 78 degrees Fahrenheit. If you have a thermometer, place it in the tank and read it after a few hours to confirm. Check that water is flowing out of the filter and that there are no leaks around the seams or the filter intake.

Test water chemistry if your tap water contains chlorine

Many municipal water systems add chlorine to kill bacteria, which is safe for humans but can harm fish and damage the beneficial bacteria your tank needs. If your tap water is chlorinated, you have two options: let the water sit uncovered for 24 hours (chlorine evaporates into the air), or add a dechlorinator product according to the package directions.

You can find out whether your tap water is chlorinated by calling your local water utility or checking their website—most list this information publicly. If you are unsure, using a dechlorinator is the safer choice and costs only a few dollars. Add it to the tank after you fill it but before you turn on the filter, or follow the product instructions if they differ.

Wait 3 to 7 days before introducing fish

Even after 24 hours of running, a brand-new tank does not yet have the bacteria colonies that keep fish waste from poisoning the water. These bacteria grow on the filter media, gravel, and tank surfaces over time. Running the tank empty for 3 to 7 days allows this process to begin. You can speed it up slightly by adding a bacterial starter product, which introduces these bacteria directly, but the tank will develop them on its own if you wait.

During this waiting period, continue running the filter and heater. Do not add fish yet. If you have a water test kit, you can test for ammonia and nitrite—both should read zero or very close to zero before fish go in. If you do not have a test kit, waiting the full 7 days is the safest approach.

Do a final visual check before adding your first fish

Before you introduce fish, look at the tank one more time. The water should be clear, not cloudy. The heater should be warm to the touch (but do not grab it—it gets hot). Water should be flowing steadily out of the filter. There should be no leaks, no floating debris, and no strong chemical smell.

If the water is still cloudy after 24 hours, wait another day—fine particles sometimes take longer to settle. If you see a leak, drain the tank, find the source, and fix it before adding water again. Once everything looks and feels right, you are ready to add your first fish according to the stocking plan for your tank size.

Frequently Asked Questions

Can I use soap to clean a new aquarium?

No. Soap leaves a residue that harms fish and can damage filter media. Rinse everything with plain tap water only. If you are concerned about manufacturing residue, rinsing thoroughly two or three times is enough.

How do I know if my tap water has chlorine in it?

Call your local water utility or visit their website—most list whether chlorine is added. If you smell a bleach-like odor from your tap water, it almost certainly contains chlorine. When in doubt, use a dechlorinator product; they are inexpensive and take the guesswork out.

What if my tank is still cloudy after 24 hours?

Cloudiness usually comes from fine particles in the gravel or from bacteria blooms. Wait another 24 hours and the water will often clear on its own. If it stays cloudy after 48 hours, do a partial water change (remove and replace about 25 percent of the water) and wait again.

Do I need a water test kit before adding fish?

A test kit is helpful but not required. If you wait the full 7 days with the filter running, the tank should be safe. A kit lets you confirm ammonia and nitrite are at zero, which gives you more confidence. Basic kits cost $20 to $30 and last for many tests.

Can I add fish after just 24 hours if I use a bacterial starter?

A bacterial starter speeds up the process, but waiting at least 3 days is still safer. The bacteria need time to establish and multiply. Adding fish too soon, even with a starter, risks ammonia spikes that can stress or kill fish.