Aquarium water conditioner
A water conditioner treats tap water to make it safe for fish, primarily by neutralising chlorine and chloramine, both of which are added to UK tap water for human safety but are harmful to fish. Adding conditioner at every water change, and whenever setting up a new tank, is standard practice rather than an optional extra.
What conditioner actually removes
UK tap water is treated with chlorine or chloramine to make it safe to drink, but both are toxic to fish even at the low levels present for human use. A water conditioner neutralises these chemicals, making otherwise unsuitable tap water safe to add to a tank.
Many conditioners also bind heavy metals such as copper, which can leach from household plumbing, and some include an additive to support a fish's natural slime coat, which can be disrupted during handling or a stressful water change. Check the specific product's label for what it covers, since formulations vary between brands.
When and how to use it
Add conditioner to tap water before or as it goes into the tank, following the dosing instructions on the specific product for your tank's volume — under-dosing risks leaving chlorine or chloramine untreated, while significant over-dosing is unnecessary and wasteful rather than beneficial.
Use it at every partial water change, not just when first setting up a tank, since every addition of fresh tap water carries the same chemicals that need neutralising. Conditioning water in a separate container before adding it to the tank is common practice, particularly for larger water changes.
Conditioner treats the water chemistry issue but does not replace proper filtration or an established nitrogen cycle in the tank — those are separate, ongoing parts of keeping water quality stable rather than something a conditioner substitutes for. Some conditioners are formulated to also support the beneficial bacteria that drive the nitrogen cycle, which is worth knowing if you are cycling a new tank rather than simply topping up an established one.
Common questions when starting out
New tank owners sometimes assume tap water is fine to add directly if it looks and smells normal, but chlorine and chloramine are not detectable by sight or smell at the levels used in UK water treatment, which is exactly why a conditioner is used every time rather than only when water looks obviously unclean.
If you keep a planted tank or invertebrates alongside fish, check that a conditioner is suitable for those too, since some product features are aimed specifically at fish and may need checking against other tank inhabitants. Shrimp and snails in particular can be more sensitive to copper than fish are, so a conditioner marketed on copper removal is worth double-checking against invertebrate-specific guidance before use.
Keep a bottle of conditioner on hand for emergencies too, not just routine changes — a burst pipe, a top-up after evaporation, or an unplanned water change all call for the same treatment as a scheduled one, and reaching for an untreated bucket of tap water in a hurry is an easy mistake to make.
What we stock
Everything below is in stock with us, priced with delivery worked out, and packed and posted by hand in the UK.
Tetra Goldfish Flakes
Complete goldfish flakes in several pack sizes, with a shared formula across the family
From£3.02
Tetra Goldfish Granules
Complete granules for goldfish, with a shared formula across both pack options
From£3.98
Tetra Prima Mini Granules
Slow-sinking granules for mid-water and bottom-feeding fish, blending herbivore and omnivore diets
£6.10
Tetra Aquasafe
A water conditioner that neutralises chlorine and heavy metals, with an added vitamin B mix
From£6.41
Tetra Pond Fish Food Variety Sticks
Complete Tetra Pond Variety Sticks in three colours, across four pack sizes
From£6.41
Tetra Koi Pond Fish Food Sticks
Complete fast-soaking Tetra Pond Koi Sticks, available in four pack sizes
From£6.41
Tetramin
Complete TetraMin flake food for ornamental fish, offered across several pack sizes
From£2.39
Tetra Temperate Flakes
Complete flakes for subtropical fish kept at 18–23°C, with vegetable ingredients
£6.99
Tetra Pond Fish Food Sticks
Complete fast-soaking Tetra Pond Sticks for pond fish, in seven pack sizes
From£4.77
Tetra Japan
Sinking dry pellets for fancy goldfish, with pack-specific label information shown clearly
From£4.56
Common questions
- Do I need a water conditioner for tap water?
- Yes, for any tank using UK tap water. Chlorine and chloramine, both added during water treatment for human safety, are harmful to fish and are not removed just by letting water stand, in the case of chloramine. A conditioner neutralises them so the water is safe to add to a tank.
- How much water conditioner should I use?
- Follow the dosing instructions on the specific product for your tank's actual water volume. Under-dosing can leave chlorine or chloramine untreated, so measure your tank volume properly rather than guessing, particularly for a new or recently changed tank.
- Do I need conditioner every time I do a water change?
- Yes. Every addition of fresh tap water carries the same chlorine or chloramine that needs neutralising, so conditioner is needed at every partial or full water change, not only when a tank is first set up.
- Does water conditioner replace a filter?
- No. A conditioner treats the chemical safety of the water itself, while a filter and an established nitrogen cycle manage ongoing water quality and waste. Both are needed together, and one does not substitute for the other.
Related
Written by Matt Garnett, who runs Giddy Pets and is a lifelong pet owner — not a vet. This is general information, not veterinary advice, and it cannot replace an examination by the vet who knows your animal. How we write these guides.