Setting up your first aquarium is exciting — but there's one step new fishkeepers skip more often than any other, and it's the one that causes the most heartbreak: treating the water before it goes anywhere near your fish.
Here in Sydney, it's easy to assume tap water is "just water." It's safe to drink, so surely it's safe for a fish tank? Unfortunately, the very thing that makes it safe for us is what makes it dangerous for them.
Chlorine vs. Chloramine — why it matters
Most people have heard that tap water contains chlorine, and that letting a bucket sit out overnight will "get rid of it." That advice isn't wrong — for chlorine alone. The problem is that many Australian water utilities, including Sydney's, use chloramine, a combination of chlorine and ammonia, rather than chlorine on its own.
Chloramine is more stable than chlorine. It doesn't evaporate out of standing water the way chlorine does, so leaving a jug on the bench overnight won't make it aquarium-safe. It will still be there the next morning, quietly stressing your fish and damaging the beneficial bacteria in your filter that keep your whole tank healthy.
What chloramine actually does to a tank
If untreated water goes straight into your aquarium, a few things can happen:
- Chlorine and chloramine irritate and damage fish gills, making it harder for them to breathe
- The ammonia component of chloramine can build up and become toxic on its own
- Your filter's beneficial bacteria — the ones responsible for breaking down fish waste — can be wiped out, effectively "restarting" your tank's cycle
None of this happens all at once, which is part of why it catches people out. Fish might seem fine for a day or two before symptoms show up: gasping at the surface, lethargy, or a cloudy, unstable tank a few days after a water change.
The fix is simple (and cheap)
You don't need anything complicated — just a water conditioner formulated to handle both chlorine and chloramine, not just chlorine. Look at the label: a basic dechlorinator may only neutralise chlorine and leave the ammonia behind, while a broader conditioner will neutralise both.
A few drops treats a full water change in seconds, and it becomes second nature after your first few tank maintenance sessions. It's genuinely one of the cheapest and easiest habits to build early — and one of the few that can make or break your first few weeks with a new tank.
Our take
Every kit and setup we put together is built around this from day one — our water treatment recommendations are chosen specifically because they handle chloramine, not just chlorine, which matters more here in Sydney than in many other parts of the world. If you're just getting started, it's worth checking whatever conditioner you already have on hand and confirming it covers chloramine too.
Got questions about your specific setup? Send us a message — we're always happy to help a fellow Sydney fishkeeper get their water right from day one.