Aquarium water treatments
This aisle does two different jobs: conditioning tap water so it's safe to add to a tank, and treating a specific health problem once you've actually identified one. Confusing the two — dosing a treatment as routine maintenance — is the most common mistake in this part of the hobby.
Conditioning new or topped-up water
Tap water contains chlorine or chloramine, both of which are safe for humans but harmful to fish, so a conditioner is used every time you add fresh tap water to a tank, whether that's a full change or just topping up evaporation. Most conditioners also add a synthetic slime coat to help protect fish through the process of a water change.
This is routine maintenance, not treatment for a problem, and it's needed every single time new tap water goes into the tank, not just occasionally.
Treating a specific problem, not dosing just in case
Products aimed at fungus, fin rot or parasites are formulated for that specific issue and are meant to be used once you've identified a problem, not added routinely to a healthy tank. Using a treatment without an actual problem to treat can disrupt the tank's biological balance for no benefit.
If you're not sure what you're looking at — unusual spots, torn fins, fish behaving oddly — it's worth confirming what the issue actually is, through research or an aquatics specialist, before reaching for a treatment aimed at a different problem.
Reading the label properly
Every treatment and conditioner has its own dosing instructions specific to tank volume, and following the product's own label is the right approach rather than applying a general rule across different brands or products. Instructions vary enough between products that assuming they're all the same is how tanks end up over- or under-dosed.
Some treatments affect filter bacteria, so check the label for any warning about that before dosing a tank with an established biological filter, and be prepared to monitor water quality more closely for a few days afterwards.
In this section
Everything below is in stock with us, priced with delivery worked out, and packed and posted by hand in the UK.
Large Aquarium Maintenance Set
A 48-inch condensation tray, a 22-inch glass scraper, a digital thermometer and 250ml of AquaSafe for a big tank.
£32.49
Supa Aquarium Net
Supa aquarium nets in coarse and fine meshes for fish catching and tank maintenance
From£1.65
Marina Digital Aquarium Thermometer
A digital aquarium thermometer that mounts on the outside of the glass and reads easily
£3.49
Marina Deluxe Aquarium Scraper
A four-in-one aquarium tool: two pad faces, a scraper blade and a planter fork
£8.79
Marina Floating Aquarium Thermometer
A floating aquarium thermometer with a safe-zone marker for tropical fish
£3.49
Tetra Test Strips 6in1 X10 Strips
Six-in-one aquarium test strips, results in 60 seconds, 10 to a pack
£7.74
Tetra Pond Medifin
A broad-spectrum pond fish treatment for bacterial, fungal and parasitic problems, wound-safe
From£11.34
Tetra Aquasafe
A water conditioner that neutralises chlorine and heavy metals, with an added vitamin B mix
From£6.41
Tetra Easy Balance
A freshwater aquarium treatment that Tetra say reduces how often you need a full water change, to as little as once every 3 to 6 months.
From£5.99
Aquarian Tap Water Safe
A tap water conditioner for tropical and goldfish tanks, added at water changes
£3.95
Supa Tonic Salts
A freshwater aquarium tonic salt for conditioning, outbreaks and brine shrimp hatching, 250G
£2.19
Supa Pond Blocks
Slow-release pond blocks that hold algae back rather than clearing it once it's bloomed
£3.65
Common questions
- Do I need a conditioner every time I do a water change?
- Yes — any time fresh tap water goes into the tank, whether a full change or just topping up, it needs treating for chlorine or chloramine first. Skipping it isn't safe just because it's a small top-up.
- Can I use more than one treatment at once?
- Generally avoid mixing treatments unless a product specifically says it's compatible with another, since combining them can have unpredictable effects on fish and on the tank's biological filter. Treat one issue at a time where possible.
- Will a treatment harm my filter's good bacteria?
- Some can, particularly stronger medicated treatments, so check the label for any warning about biological filtration before dosing an established tank. If in doubt, remove carbon filter media during treatment as many labels advise.
- My fish still look unwell after treating — what now?
- If a treatment hasn't resolved the issue within the timeframe the label describes, it's worth getting a second opinion from an aquatics specialist rather than repeating the same treatment or trying a different one at random, since the original diagnosis may have been wrong.
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.