Starting a New Tank
Setting up an aquarium is straightforward if you do the steps in the right order — and the order is not "fill it and add fish the same day."
Key facts
- Fish go in last, after the tank has cycled — not on day one.
- Tap water needs a dechlorinator before it touches fish or filter bacteria: chlorine and chloramine are toxic to both.
- New fish should be acclimated gradually to a tank's temperature and water chemistry, not tipped straight in.
The order that works
- Rinse the substrate and decor.
- Arrange the hardscape.
- Install and run the equipment — filter, heater.
- Fill with water treated with a dechlorinator.
- Cycle the tank — before any fish go in.
- Add fish gradually, not all at once.
Why the water needs treating first
Chlorine and chloramine in tap water are safe for people but damage fish gills and kill the nitrogen-cycle bacteria the whole filter depends on. Water conditioners — Seachem Prime, for example — neutralize chlorine, chloramine and ammonia; they're used both at initial fill and at every later water change.
How long before the first fish
An unseeded natural cycle is commonly cited at roughly 3-6 weeks — the full breakdown of that figure, and where it comes from, is in the separate nitrogen-cycle guide. Seeding with mature filter media or a bacterial starter product can shorten it considerably.
Bringing the first fish home
A sealed fish bag is commonly floated in the tank for about 15-20 minutes to match temperature. After that, fish are drip-acclimated — gradually mixing tank water into the bag — typically over 30-60 minutes for most fish and 60-90 minutes for shrimp, wild-caught or sensitive species such as discus; if the store's water differed noticeably in pH or temperature, a longer window is recommended. Tank lights are commonly left off during and shortly after this process.