How to Clean a Fish Tank: 8-Step Aquarium Cleaning Guide

Lay out everything before you start: a fish net, water conditioner, a clean 5-gallon bucket dedicated to fish use only, and a gravel vacuum (also sold as an aquarium siphon). A thermometer is handy for matching refill water temperature.

Unplug both the heater and the filter at the wall. Heaters crack if they run while exposed to air, and filters can burn out their motor. Walking through the room and seeing them already unplugged is your reminder not to skip this step.

Scoop about half a gallon of tank water into a clean bowl. Then gently net your fish and place them into that bowl. Using the original tank water keeps them from going into temperature or pH shock while you work.

If you're only doing a partial water change and the gravel vacuum is doing most of the work, you can skip this step and leave the fish in the tank. For a deep clean - which this video shows - moving them out gives you full access.

Lower the wide plastic tube of the gravel vacuum into the tank. Hold the hose end over your bucket, sitting lower than the tank so gravity does the work. Move the wide tube up and down quickly a few times to prime it.

Water fills the hose and the siphon catches. Once it's running, the tank will keep draining until you pull the tube out or pinch off the hose.

Push the wide tube straight down into the gravel and stir gently. Sediment swirls up into the tube while the gravel falls back. Work spot to spot in a grid so you cover the whole bottom rather than missing sections.

Keep the intake submerged. If it breaks the water surface, air enters the tube and the siphon stops. Stop when about a third of the tank water is in the bucket - that's a healthy partial water change.

With the water level down, the inside of the glass is easy to reach. Use an algae scraper, a magnetic cleaner, or an aquarium-safe pad to wipe the green biofilm off the walls. Push down to the gravel line, then back up - the smear lifts right off.

A magnetic algae cleaner is the gentlest option for acrylic tanks because it doesn't scratch the surface. For glass tanks, a plastic-blade scraper works faster on stubborn spots.

Take out the filter unit and pop open the housing. Pull out the sponge or cartridge. Swish it in the bucket of old tank water you just drained until the worst of the gunk falls off, then put it back in the filter.

Never rinse the filter media in tap water - chlorine kills the beneficial bacteria that keep your fish alive. Always rinse in old tank water you just drained. If the cartridge is shredded or more than 4-6 weeks old, swap it for a new one instead of rinsing.

Wipe the outside of the glass with a clean damp cloth - no soap, no glass cleaner, no Windex. Even a little residue can drip in. Wipe the upper rim too, where evaporation leaves a hard-water line.

Rinse any decorations or fake plants you removed under plain running water. Skip soap entirely. Wipe down the lid and any other parts going back into the tank.

Fill a pitcher with tap water. Feel the temperature against your wrist - it should match the tank, not too cold or too hot, since fish are sensitive to swings. Add the correct dose of water conditioner per gallon (one drop per half gallon for Seachem Prime), stir, and slowly pour the treated water back into the tank.

Plug the heater and filter back in. Float the bowl with your fish on top of the tank for about 10 minutes so the water temperatures equalize, then gently net them back in. Cloudiness clears within an hour as the filter circulates.