Water conditioner and starter bacteria: essential or just marketing?
Published by Planète Pets · managing editor: Clément Lacaille · how our guides are written
A nuanced verdict: the water conditioner is genuinely essential, while starter bacteria are a useful accelerator but not magic. The first neutralizes the chlorine and heavy metals in tap water within minutes — both toxic to fish and bacteria. The second shortens cycling but never replaces it. Budget for both: 15 to 30 €.
Contents · 5 sections
What exactly does a water conditioner do?
Tap water contains chlorine or chloramines, added to protect us but which burn fish gills and kill the bacteria in your filter. The conditioner (5 to 15 € a bottle, a few cents per water change) neutralizes chlorine, chloramines and heavy metals (copper, lead from the pipes). Use it at every water change, dosed on the volume you add, not on the volume of the tank.
Do bottled bacteria actually work?
Yes, partially. These products (10 to 20 €) seed the tank with nitrifying bacteria — the ones that convert ammonia into nitrites and then nitrates. They can shorten cycling from 4 weeks to 2 or 3, but no bottle makes a tank safe to stock in 24 hours, whatever the label claims. The full process is explained in our guide to water tests and the nitrogen cycle.
How do you use these two products properly?
- At start-up: conditioner in the fill water, then bacteria poured directly onto the filter media.
- Always verify with a test: only add fish once the nitrite spike has fallen back to zero.
- At every water change: conditioner without fail; bacteria are pointless if the tank is running well.
- After medication or a deep clean: a dose of bacteria helps the filter get going again.
- Storage: keep the bacteria bottle away from heat, and respect the use-by date.
Is there a free alternative?
Two, actually. For chlorine: leaving water to stand for 24 hours in an open container lets it evaporate (but not chloramines or metals). For bacteria: squeezing a filter sponge from a healthy tank into the new filter is the most effective seeding there is, as every fishkeeper with several tanks knows. Our other water-quality guides are in the care and grooming category.
Frequently asked questions
Can you overdose the conditioner?
The safety margins are wide: a slight overdose is harmless. Still, stay close to the recommended dose, especially with shrimp.
Do bacteria need to be added regularly?
No. Once the tank is cycled, the colony sustains itself in the filter and substrate. The maintenance top-up doses sold in pet shops are unnecessary.
Can conditioner and bacteria be poured in together?
Add the conditioner first, wait a few minutes, then the bacteria: otherwise the still-active chlorine kills part of the bottle.
See it in the Planète Pets shop: Hang-on isolation and breeding box for aquariums (€28.90) · the whole shop
This guide is part of Planète Pets’s Fishkeeping universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.
