The basic steps for draining your aquarium
To empty an aquarium, you'll turn off the filter and heater, remove the fish to a temporary container, siphon or pump out the water, and then take out the substrate and decorations. The whole process takes 30 minutes to an hour depending on tank size. The key is doing this in the right order so your fish stay safe and your equipment doesn't get damaged.
Most people empty an aquarium for one of three reasons: a complete tank cleaning, moving the tank to a new location, or dealing with a water quality emergency. Each situation follows the same basic steps, but the urgency and what you do with the water afterward changes slightly.
Key Takeaways
- Turn off the filter, heater, and air pump before you start removing water, so you don't run equipment dry or damage it.
- Move your fish to a clean bucket or container filled with water from the tank before you drain it, so they stay in familiar water while you work.
- Use a siphon or submersible pump to remove water, not a net or pitcher, because these methods are faster and less likely to stir up debris.
- Save some of the old water if you're doing a partial water change or refilling the same tank, because it contains beneficial bacteria your fish need.
- Let the tank sit empty for at least 15 minutes before refilling if you're cleaning the substrate, so algae and trapped waste can dry out.
Prepare your equipment and turn off power
Before you touch the water, flip the switch on your filter, heater, and air pump. These devices are designed to run submerged, and running them dry will burn out the motor or heating element. If you have a power strip, turning off the whole strip at once is the safest approach.
Wait five minutes after turning off the heater before you start draining. This gives the heating element time to cool so you don't burn yourself if you accidentally touch it while working. Check that the heater is no longer warm by holding your hand near it—not touching it directly.
Move your fish to a temporary container
Use a clean bucket, storage container, or spare aquarium to hold your fish while you drain the main tank. Fill this container with water from your aquarium—not tap water—so the fish stay in water they recognize. If you're draining a large tank with many fish, you may need two containers so they don't get crowded.
Use a net to catch each fish gently and place it in the temporary container. Work slowly and keep the lights dim if possible, because sudden movement and bright light stress fish. If a fish is hiding or hard to catch, you can drain the tank partially first (down to a few inches) and then net it more easily. Never squeeze a fish or grab it with your bare hands, because this removes the protective slime coating on its scales.
If you have delicate fish like bettas or fish with long fins, use a soft mesh net or even a clear cup to scoop them instead of a regular net. Cover the temporary container loosely with a towel to keep the fish calm and prevent them from jumping out.
Siphon or pump out the water
A siphon is a tube that uses gravity to pull water from the tank into a bucket on the floor. To start a siphon, fill the tube completely with water, pinch both ends to keep the water inside, place one end in the tank and one end in your drain bucket, then release. Water will flow out as long as the bucket end stays lower than the tank. This method is free if you already have tubing, but it takes longer for large tanks.
A submersible pump is a small electric device you place in the tank that pushes water out through a hose. This is faster than a siphon and works well for tanks over 20 gallons. Pumps cost $20 to $50 and can be reused for future water changes. Plug the pump into an outlet, place the outlet hose in your drain bucket, and turn it on.
As you drain, watch the water level and stop before the filter intake sits above the water line. If your filter has an intake tube, it will suck air and make noise once the water gets too low. For a complete drain, you can let it go all the way down, but for a partial water change, stop when you've removed the amount you need.
Remove substrate and decorations
Once the water is mostly drained, use a net or your hand to scoop out any remaining gravel, sand, or substrate. Place it in a separate bucket—do not throw it away yet if you plan to reuse it. Substrate holds beneficial bacteria, so keeping it is better than replacing it if your tank is healthy.
Take out decorations, plants, and hiding spots one at a time. If algae or debris is stuck to them, rinse them in the old aquarium water you've saved, not under tap water. Tap water can kill the bacteria on the surfaces. If you need to scrub something, use a soft brush and only the old tank water—never soap or chemicals.
If you're doing a deep clean of the tank itself, now is the time. Use a soft cloth or algae scraper to wipe the inside glass, but do not use any cleaning products. Rinse the cloth in old tank water only. Let the empty tank sit for 15 minutes so any remaining debris can settle and dry slightly.
Refill the tank with fresh water
If you saved old water, pour it back into the tank first. This water contains beneficial bacteria that keep the tank stable. Then add fresh, dechlorinated water to bring the tank back to its normal level. If your tap water is heavily chlorinated, let it sit in an open bucket for 24 hours before adding it, or use a water conditioner product to remove chlorine when ready.
Turn the heater back on and let it warm the water for 15 to 20 minutes before you return the fish. Check the temperature with a thermometer—it should match the temperature of the water in the temporary container, or be within 2 degrees. If the tank is much warmer or cooler, wait longer or add some of the temporary container water to the tank to bring temperatures closer.
Turn the filter back on once the heater is running and the water is warm. The filter will take a few minutes to prime (fill with water) and start flowing smoothly. You may hear air bubbles or gurgling for the first minute—this is normal.
Return the fish and monitor the tank
Pour the fish from the temporary container slowly into the tank, or use a net to move them one at a time. If you poured water from the temporary container into the main tank during the refill, the fish will adjust more easily. Watch them for the first 30 minutes—they may hide or act stressed, which is normal after being moved.
Do not feed the fish for at least two hours after returning them to the tank. Feeding stressed fish can cause them to refuse food or get sick. After two hours, offer a small pinch of food and watch to see if they eat normally. If they ignore it, wait until the next feeding time.
Check the water parameters (pH, ammonia, nitrite, nitrate) the next day if you have a test kit. A complete water change can shift these values, and knowing the results helps you decide if a partial water change is needed in the coming days. If ammonia or nitrite are above zero, do a 25 percent water change the following day to bring them back down.
Common mistakes to avoid
Do not drain the tank while the filter is still running—you'll damage the motor. Do not use tap water without letting it sit or treating it first, because chlorine can harm fish and beneficial bacteria. Do not refill the tank with water that is much warmer or cooler than the temporary container, because sudden temperature shifts stress fish and can cause disease.
Do not throw away the substrate or decorations unless the tank had a disease outbreak. Beneficial bacteria live on these surfaces, and replacing them means the tank has to cycle again before it's stable. Do not feed the fish right after moving them back, and do not overcrowd the temporary container—both cause stress and water quality problems.
Do not use soap, bleach, or aquarium-specific cleaners on the inside of the tank unless you rinse it extremely thoroughly afterward. Even small amounts of soap can harm fish. If you need to disinfect the tank due to disease, use a 10 percent bleach solution, rinse it at least five times with tap water, then let it air dry for 24 hours before refilling.
Frequently Asked Questions
How often should I empty my aquarium?
Most aquariums do not need a complete empty more than once or twice a year. Instead, do a 25 to 50 percent partial water change every week or every other week, depending on tank size and how many fish you have. A complete empty is usually only needed for deep cleaning, moving the tank, or treating a disease.
Can I use the water I drained to water my plants?
Yes. Aquarium water is rich in nitrogen from fish waste and is excellent for houseplants and gardens. Store it in a clean bucket and use it within a few days, or it may develop algae or smell bad. Do not use it if you treated the tank with medication.
What if I don't have a siphon or pump?
You can use a large cup or pitcher to scoop water out, but this takes much longer and stirs up debris. For a 10-gallon tank, this method takes 20 to 30 minutes. For anything larger, borrowing or buying a siphon is worth the time saved.
How long can fish survive in a temporary container?
Fish can survive in a bucket for several hours if the water is from their tank and the container is not overcrowded. For a complete tank empty that takes an hour or two, a temporary container is fine. If you need to keep fish out of the tank for more than four hours, add an air stone or small battery-powered air pump to the temporary container to keep oxygen levels up.
Do I need to replace the filter media when I empty the tank?
No, unless it is visibly clogged or falling apart. Rinse the filter media in old tank water only—never tap water—to remove debris while keeping the beneficial bacteria alive. Replace filter media only every three to six months, depending on how dirty it gets.