Aquarium Cleaning and Water Treatment

Clean, chemically balanced water is a basic requirement for a healthy aquarium – and yet caring for water quality is one of the most commonly underestimated aspects of fishkeeping. Tap water that looks clean and clear can contain chlorine, chloramine, heavy metals or unsuitable pH and hardness levels that are directly toxic or harmful to aquarium fish in the long term. Never put aquarium fish into untreated tap water – even brief exposure to chlorine or chloramine can damage the gills and lead to death.

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Looking after water quality in an aquarium is a continuous process requiring regular attention, the right products and a basic understanding of water chemistry. Water parameters are constantly changing due to biological processes, feeding, fish metabolism and evaporation – without regular monitoring and maintenance, even a well-established aquarium can reach a critical state within weeks.

Key water quality parameters in an aquarium

Before choosing the right products, it's important to understand which water parameters are crucial for aquarium fish:

• pH – a measure of the acidity or alkalinity of water on a scale of 0–14. Most tropical freshwater fish prefer a pH of 6.5–7.5. Significant deviations or sudden pH changes cause stress and gill damage. pH changes over the course of the day due to plant photosynthesis – it's lower in the morning and higher in the evening.
• Water hardness (GH and KH) – GH (general hardness) reflects the mineral content of the water, while KH (carbonate hardness) stabilises pH and prevents it from fluctuating. Different fish species prefer different hardness levels – soft water for tetras and discus, hard water for African cichlids. KH below 3°dH causes dangerous pH swings.
• Ammonia (NH3/NH4+) – a toxic waste product of fish metabolism. In a healthy, established aquarium, ammonia should be 0 mg/l – any measurable level signals an overloaded biological filter or a temporary crisis.
• Nitrites (NO2) – intermediate products of the nitrogen cycle that are toxic to fish. Like ammonia, they should be 0 mg/l in an established aquarium. Elevated nitrites signal a disruption to biological filtration.
• Nitrates (NO3) – the final product of the nitrogen cycle, less toxic than ammonia and nitrites. They build up in the aquarium and are removed through regular water changes. Levels below 25 mg/l are safe for most species.
• Chlorine and chloramine – disinfectants added to drinking water that are toxic to aquarium fish and the biological filter. They must be neutralised before every water change.

Regular water changes

Regular partial water changes are the single most important maintenance routine for any aquarist. No filter or product can fully replace them – water changes remove accumulated nitrates, restore the mineral balance and bring fresh trace elements into the aquarium.

• Change 20–30% of the water volume every week – or 10–15% every two weeks for less densely stocked aquariums.
• Always treat new water with a conditioner before adding it to the aquarium – neutralising chlorine and chloramine is essential with every water change.
• New water should be the same temperature as the water in the aquarium – a difference of more than 2–3°C causes temperature shock.
• When changing the water, always siphon detritus from the substrate with a gravel cleaner – accumulating organic waste is a source of ammonia and nitrites.

What you'll find in the Aquarium Cleaning and Water Treatment section

• Water treatment chemistry – conditioners that neutralise chlorine and chloramine, and products for adjusting pH, hardness and osmotic values. Essential for every water change and when setting up a new aquarium.
• Algae control products – algicides and biological products for controlling unwanted algae growth. Algae are a natural part of every aquarium, but overgrowth spoils its appearance and threatens the health of plants and fish.
• Aquarium cleaning products – glass scrapers, gravel cleaners, chemical cleaners and biological products that support the breakdown of organic waste. Regularly cleaning the glass and substrate is a basic hygiene routine for every aquarist.

How to test water quality in an aquarium

Regular testing of water parameters is the only reliable way to catch problems before they affect your fish's health:

• Test strips – quick and affordable, but less accurate. Suitable for regular, approximate checks. They measure pH, KH, GH, NO2 and NO3 in a single dip.
• Liquid drop tests – more accurate than strips, suitable for regular measurement and for troubleshooting. Available as kits for both freshwater and marine water.
• Digital meters – electronic devices for precisely measuring pH, TDS, conductivity or temperature. Suitable for demanding aquarists and setups requiring precise control of parameters.
• Test water parameters at least once a week in an established aquarium and daily when setting up a new aquarium or when dealing with fish health problems.

Practical tips for aquarium cleaning and water treatment:

• Never change more than 50% of the water at once – a large change causes sudden shifts in parameters and stresses the fish. The exception is a crisis situation with extremely high levels of toxic substances.
• Prepare water for changes in advance – let it stand or aerate so it reaches room temperature and any excess CO2 can escape.
• When you have water quality problems, always identify the cause first – adding products without understanding the cause of the problem often only masks the situation rather than improving it.
• Dose all water treatment products exactly according to the instructions – overdosing can be just as harmful as the problem you're trying to solve.
• Keeping a simple log of water parameters is a habit of experienced aquarists – recording values over time lets you spot trends quickly and prevent problems.

Clean, chemically balanced water is the foundation of a healthy, beautiful aquarium. Regular water changes, the right products and regular testing of parameters are simple routines that will save you a lot of worry and give your fish a long, healthy life.