How to Clean Your Fish Tank

Help your aquarium fish stay healthy and happy by maintaining a clean tank and clear water. You may need to regularly add pre-prepared water. Cleaning your fish tank is not difficult, especially when you stick to a schedule that prevents the buildup of organic materials that promote algae growth. Whether it's a freshwater or saltwater tank, you can keep it clean without too much time or effort.

Prepare the necessary tools and cleaning supplies for your fish tank. Ensure that you have everything you need, including water treatment products, before starting. Check the list of required items to make sure you have the tools and workspace ready.

• A sufficient amount of treated water to replace the water in the tank, or water treatment chemicals to remove chlorine from tap water
• A scraper to clean the inside glass of the tank (sponge scrubber, straight-edge blade, or a combination of both)
• A 20-liter bucket dedicated to fish tank cleaning
• A simple gravel siphon (NOT a battery-powered type)
• Filtration materials (filter box, filter foam, activated carbon bags, etc.) if a filter replacement is needed this time
• Specialized glass cleaner for fish tanks or a vinegar-based glass cleaner solution
• 60 ml bleach for every 10-15 liters of water in a separate bucket (optional)
• A metal or plastic scraper blade (optional, be careful with acrylic tanks as this material is more prone to scratches)

Use an algae scraper to clean the tank walls. Scrub the glass surface, working in small sections if necessary to remove algae buildup. For stubborn algae, use a metal or plastic scraper to scrape it off.

• You may need to wear gloves for this task, especially if you're allergic to anything in the tank (like synthetic salt mixes). Opt for long rubber gloves made for cleaning fish tanks.
• Avoid using kitchen sponges or dishwashing sponges, or any items with soap residue or chemical cleaners. Only use a dedicated algae scrubber to prevent soap or chemicals from contaminating the tank.
• This step can also be done after removing 10-20% of the water from the tank.

Decide how much water you will replace. Consider the organic load (rate of organic buildup) in the tank when determining how much water to change and how often. Aim to replace 25-50% of the water weekly.

• If your goal is to minimize nitrate and phosphate levels, you’ll need to replace a larger amount of water (50% or more) and do it more frequently. Once you’ve replaced a significant amount (50% or more), you may need to change water less often.
• Note that changing 10% of the water every week is better than changing 40% once a month.

Remove the old water. Start by using a siphon to remove the old water into a 20-liter bucket. It’s best to buy a new bucket and dedicate it solely to fish tank cleaning—don’t use it for laundry or dishwashing, as synthetic cleaning chemicals are harmful to fish.

• You can purchase a siphon hose designed for fish tanks, with a hook for attaching to the sink. Be sure to read the instructions for proper use. This type of siphon also helps prevent water overflow.
• You can use the same siphon to refill the tank with water afterward.

Clean the gravel. Move the siphon through the gravel bed. Fish waste, leftover food, and other debris will be sucked into the vacuum. If your fish are very small, weak, or delicate, you can cover the siphon’s end with a clean mesh cloth.

• Clean at least 25-30% of the gravel each month.
• If your tank has a sand substrate, slow the flow by covering the siphon’s end with your finger or tightening the hose. Hold the siphon about 2.5 cm from the sand surface or closer to suck up debris without disturbing the sand. Gently rake or stir the sand (if no animals are buried underneath) to remove debris and prevent the formation of anaerobic areas.

Clean the decorations. Algae thrive due to nutrients in the water and light exposure, so decorations in your tank may accumulate algae. Use an algae scrubber or a soft, unused toothbrush to clean the decorations while siphoning out water. Avoid soap, as it can harm your fish!

• If cleaning decorations is difficult, remove them from the tank and soak them in a large bucket of water mixed with 60 ml bleach for 15 minutes. Rinse everything thoroughly and treat with a water conditioner. If there are porous materials, let them dry completely before returning them to the tank.
• If algae buildup is excessive, reducing organic matter or light levels in the tank can help. You might cover windows, move the tank away from the window, or adjust the lighting schedule. Another option is to replace water more frequently or in larger quantities.
• Consider adding frogs, tank-cleaning fish, or plecos to your larger tank to prevent excessive algae growth.

Fill the tank with clean water. Add back the amount of water you removed with treated water that matches the temperature of the tank. An infrared thermometer is the best tool for checking the temperature. Keeping the temperature within the proper range is crucial for the fish’s health. Remember, slightly warm water can be too hot for most fish species.

• Avoid overfilling the tank.
• If using tap water, you must treat it to remove chlorine, heavy metals, and other toxins that fish cannot tolerate. Choose a water conditioner with ammonia detoxifying chemicals.
• Prepare and fill a bucket with water the day before. Add the water conditioner and let it sit overnight. Be sure that the water temperature matches the tank's; a difference of more than 0.6°C can be dangerous for fish.
• If nitrate levels are too high, consider replacing the water with reverse osmosis filtered water from a pet store. Add a freshwater aquarium buffer to help stabilize the tank water.

Monitor the water. Wait a few hours for any cloudy areas to clear, and the water will become clear again. There are various water clarifiers available, but they are usually unnecessary. If the water remains cloudy, it indicates an underlying issue, and a clarifier will only mask the problem without solving it.

Clean the exterior. Wipe down the outside of the fish tank, including the glass, lights, and lid. You can use a glass cleaner, but remember to spray it onto a cloth rather than directly onto the tank to prevent chemicals from entering the tank. Use distilled white vinegar to remove mineral deposits.

• For acrylic tanks, purchase a special polish designed for this material.

Replace or clean the filter about once a month. Rinse the mechanical filter with water you removed from the tank if you don’t want to disturb the beneficial bacteria. Remove and replace the chemical filter media (such as activated carbon, GFO, or Chemi-Pure) every 2-6 weeks, depending on organic load and maintenance routine.

Prepare saltwater solution. The temperature, salinity, and pH levels must be within the recommended range for the fish species you're keeping. Begin the preparation the night before you plan to clean the tank. Purchase distilled water or reverse osmosis filtered water from a pet store.

• Store the water in a clean plastic bucket, ideally one reserved solely for this purpose.
• Warm the water using a specialized aquarium heater purchased from a pet store.
• Mix the salt. Simple salt mixtures are available at pet stores. Follow the instructions for the correct ratio based on the amount of water you're using. Usually, it's ½ cup of salt for every 4 liters of water.
• Aerate the water while dissolving the salt.
• The next morning, measure the salinity with a refractometer, hydrometer, or salinity meter. For a fish-only tank, aim for a salinity of 30 g/liter. For tanks with corals, you may need to mix salt with concentrated seawater to reach 35 g/liter.
• Check the temperature with a thermometer. The ideal temperature for saltwater fish is between 23°C and 28°C.

Prepare aquarium cleaning supplies. In addition to the basic tools needed for freshwater aquariums, saltwater tanks require special equipment. Focus on gathering the following supplies:

• A sponge for cleaning algae off the glass inside the tank.
• A 20-liter bucket dedicated solely for aquarium maintenance.
• A simple siphon gravel vacuum (NOT a battery-operated one).
• A filtration system (filter box, filter sponge, activated carbon bags, etc.) if you plan to change the filter.
• Glass cleaning solution or vinegar-based cleaner specifically for aquariums.
• pH test strips.
• A refractometer, hydrometer, or salinity meter.
• A thermometer.
• A separate 10% bleach solution in a dedicated bucket (optional).

Clean algae. Use an algae sponge to scrub away algae inside the tank. For stubborn spots, use a scraper or a plastic razor blade to remove them.

Remove water. For saltwater aquariums, it’s recommended to replace 10% of the water every two weeks. In most cases, this amount is sufficient to reduce nitrate levels. Start siphoning the water into a large bucket.

Clean the gravel. Move the siphon through the gravel layer. Fish waste, leftover food, and other debris will be sucked into the siphon. If your fish are very small, weak, or fragile, you can wrap a mesh cloth around the siphon’s tip.

• Slow down the water suction by placing a finger over the siphon end or constricting the tube if your tank has a sand substrate. Hold the siphon about 2.5 cm (or closer) from the sand surface to vacuum out waste without disturbing the sand. Stir the sand to prevent the formation of anaerobic zones.

Clean the decorative items. Use a sponge or an unused toothbrush to scrub the decorative items in the water that you just pulled out. Alternatively, you can remove the decorations from the tank and soak them in a 10% bleach solution for about 15 minutes, then rinse them thoroughly and treat them with a de-chlorinating solution.

Check for salt residue. As the saltwater evaporates from the surface of the tank, it leaves behind salt deposits. Use a sponge or a damp cloth to wipe off the salt residue and replenish the lost water.

Add more water to the tank. Carefully pour the pre-prepared water into the tank, ensuring that the salinity and temperature are consistent with the water already in the tank. Be cautious not to overfill the tank.

Monitor the temperature daily. Marine fish thrive in a relatively narrow temperature range. To ensure the well-being of the fish, it's important to check the tank's temperature every day.

• Letting water sit in a bucket for several hours can remove chlorine from tap water, but it doesn't eliminate chloramine, which is also harmful to fish. Do a favor for your fish by using a water treatment product. If your water contains chloramine, use ammonia detoxifiers like Prime. These chemicals are dangerous to fish.
• There is no need to remove the fish from the tank while cleaning it.
• Choose the right-sized siphon tube to clean the gravel. A tube that's too small will take forever to clean the tank, while one that's too large will remove too much water before the job is finished. Select a siphon hose that matches the height of the tank.
• Larger fish tanks will have more stable water parameters, as changes take longer to occur compared to smaller tanks.
• If you use a motor-driven filter, you'll need to take it apart and scrub the moving parts and mechanical sections to remove debris. Only clean the bio-wheels if absolutely necessary. Clean the shafts connected to the filter to ensure smooth operation, but avoid using any folding materials, as they provide a breeding ground for bacteria.
• If you buy a drinking-safe hose, you can make water changes in your fish tank much easier by using a siphon hose to direct the water to the drain. You can also find hose connectors to help direct water straight from the sink.
• Wear a sleeveless shirt to avoid getting your sleeves wet.

• If you use a carbon filter, replace the filter bag every 2-6 weeks, depending on the organic load and maintenance schedule. After this period, the carbon will leak waste back into the tank.
• Never use tap water to clean mechanical filters, as chlorine and chloramine can harm the beneficial bacteria.
• If you haven’t done a large water change in a while, start slow. Change a small amount of water every week. Sudden and large changes in water parameters (temperature, pH, salinity) can upset the chemical balance in the tank and shock the fish.
• Avoid removing the fish unless absolutely necessary, as this causes stress and disrupts their protective slime coat.
• Avoid using water pipes with brass connectors if you have animals sensitive to copper, such as corals.
• Be very cautious when cleaning your aquarium if you're using bleach to clean the glass. Bleach can be deadly to fish upon contact.
• Always wash your hands thoroughly before and after putting them in the tank or handling any decorations.
• Never put anything into the tank that may still have soap residue, including your hands, water pipes, or nets.

• Properly treated water sufficient for a water change
• Ammonia detoxifiers and chlorine neutralizers
• Algae scrubber sponge for cleaning the tank glass
• 20-liter bucket for aquarium cleaning
• Simple siphon gravel vacuum
• Water filtration materials (filter boxes, filter sponges, activated carbon bags, etc.)
• Aquarium glass cleaning solution or vinegar-based solution
• pH testing strips
• Thermometer
• Salt mix (for saltwater aquariums)
• Refractometer, hygrometer, or salinity testing tools (for saltwater aquariums)
• 10% bleach solution in a dedicated bucket (optional)
• Metal or plastic scraper (optional)
• Fish net (for when needed)
• Cloth