Fish Tank Cleaning Guide: Step-by-Step Process for UK Fishkeepers

What Is the Step 1: Preparation and Equipment Check?

Before starting, gather all your cleaning equipment: algae scraper or magnetic cleaner, gravel vacuum (siphon), clean bucket (used only for aquarium purposes – never use a bucket that has held cleaning products), water conditioner, and a towel for spills. Having everything ready before you start makes the process efficient and minimises the time your tank is disrupted. For related guidance, see our Fish Tank Setup Guide Uk guide.

Turn off the heater before the water level drops below it (exposed heaters can overheat and crack). Turn off the filter once you are ready to clean it, but keep it running during glass cleaning and gravel vacuuming. Unplug any air pumps if water levels will drop near the pump connection point. Leave the lights on so you can see what you are doing, but turn them off if cleaning causes significant disturbance that visibly stresses the fish. For related guidance, see our Freshwater Vs Tropical Fish Uk guide.

Do not remove the fish. A common beginner mistake is netting fish out of the tank for cleaning. This causes far more stress than the cleaning process itself and risks injuring the fish. Fish are perfectly fine remaining in the tank during routine maintenance. They will move away from the vacuum and scraper naturally. The only exception is a full tank breakdown for disease treatment, which is a separate emergency procedure, not routine maintenance. For related guidance, see our Aquarium Maintenance Schedule Uk guide.

What Is the Step 2: Glass Cleaning and Algae Removal?

Start with the inside glass, cleaning before you disturb the substrate so that dislodged algae can be siphoned out during the gravel vacuum step. Use a purpose-made algae scraper with a long handle, a magnetic glass cleaner, or an aquarium-safe sponge. Work methodically from top to bottom, overlapping strokes to ensure complete coverage.

For stubborn algae spots (green spot algae on glass), a razor blade scraper works effectively on standard glass tanks. Do not use razor blades on acrylic tanks, which scratch easily; use a soft pad specifically designed for acrylic instead. Check your tank material before choosing a cleaning tool. Hard water deposits (white crusty lines at the waterline) can be removed with a vinegar-soaked cloth, but only above the waterline and rinsed thoroughly before the area is submerged again.

The outside glass can be cleaned with a damp cloth. For streak-free results, use a microfibre cloth with plain water. Never spray glass cleaner, household cleaners, or aerosol products near the tank, as the overspray can enter the water through the surface and poison fish. Even small amounts of surfactants from cleaning products are lethal to fish. If you need to clean the stand or surrounding area, use only water and keep products well away from the tank.

What Is the Step 3: Gravel Vacuuming and Water Removal?

The gravel vacuum is a siphon tube with a wide end that pushes into the substrate. As water flows through the siphon into your bucket, debris trapped in the gravel is lifted into the water column and removed. Push the wide end into the gravel, let debris rise, then move to the next section. The gravel itself is too heavy to be siphoned out, but the waste trapped between the pieces is removed effectively.

Vacuum approximately one-third of the substrate area each week, rotating sections so the entire substrate is cleaned over three weeks. This approach avoids disturbing beneficial bacteria in the substrate all at once. Focus on areas where debris accumulates: under decorations, in corners, and beneath the filter outlet where current deposits waste.

As you vacuum, you are simultaneously removing water for your water change. Stop siphoning once you have removed 20-30 percent of the tank volume. For a 100-litre tank, this is 20-30 litres, which is roughly 2-3 standard buckets. If the water is very dirty (brown or cloudy), you may remove up to 50 percent, but larger changes risk shocking fish with sudden parameter shifts. The removed water is excellent for watering house plants, as it is rich in nitrate and natural fertilisers.

What Is the Step 4: Filter Cleaning and Decoration Maintenance?

If this is your monthly filter maintenance session, remove the filter media now. Place it in a bucket of the old tank water you just removed. Gently squeeze and swish sponge media to dislodge accumulated debris. Do not scrub, wring, or rinse vigorously; the goal is to remove the worst blockages while preserving the brown bacterial biofilm. Ceramic or bio media can be gently swirled in the old water. Replace the media in the filter and restart.

Decorations that have accumulated algae or debris can be removed and scrubbed with an aquarium-safe brush and old tank water. For stubborn algae on ornaments, soaking in a dilute bleach solution (1 part bleach to 20 parts water) for 15 minutes followed by thorough rinsing and air-drying for 24 hours is safe. The bleach dissipates completely when dry. However, never bleach porous natural materials (wood, certain rocks) as they absorb bleach and release it slowly into the tank.

Live plants should be trimmed of dead or dying leaves during cleaning sessions. Remove any floating debris, dead plant matter, or uneaten food that the gravel vacuum did not catch. If you have artificial plants, remove them every few months and scrub with an aquarium brush to prevent algae buildup. Return all decorations to their positions before refilling the tank.

What Are the Step 5: Refilling and Post-Clean Checks?

Fill your clean bucket with tap water and add the appropriate dose of water conditioner. Check the water temperature with your hand or a thermometer; it should feel the same temperature as the tank water (within 1-2 degrees Celsius). Cold water shock is a real risk, particularly in winter when UK tap water can be very cold. If needed, mix hot and cold tap water to achieve the right temperature before adding conditioner.

Pour the treated water slowly into the tank, ideally onto a plate or decoration to break the flow and avoid disturbing the substrate. Alternatively, use a jug and pour gently near the surface. Refill to the correct level, ensuring the heater is fully submerged before turning it back on. Restart all equipment and verify the filter is flowing correctly, the heater light is on, and the thermometer shows the correct temperature.

After cleaning, fish may be slightly stressed and behave cautiously. This is normal and they will resume normal activity within 30-60 minutes. Do not feed immediately after cleaning; wait at least an hour. Monitor the tank for the next few hours to ensure all equipment is functioning properly. If the water is slightly cloudy after a clean, this typically clears within 24 hours as particles settle. Persistent cloudiness may indicate a bacterial bloom, which resolves on its own.