when to add fish in new tank

When to Add Fish to New Fish Tank? (Infograph)

It’s exciting to have a new aquarium. You’ve set up the new fish tank, filled the fish tank with water, added the gravel, set up the decorations and plants, turned on the heater and filter, everything in the new fish tank is working and running smoothly. So when can you add fish into your new fish tank?

You need to wait before you add fish into your new fish tank. I remember when I set up the new fish tank in my son’s room, one of the hardest part of the new fish tank process was the wait! My son was so impatient and kept asking when to add new fish to the new tank. It felt like we were on a road trip and my son was constantly asking “Are we there yet?” However, despite the extended “Are we there yet?” it was so worth the wait because we were essentially setting up my son’s fish tank for success. Plus it was a good teaching moment to teach my son about the nitrogen cycle and why we need to let the water cycle in the fish tank.

Why Wait Before Adding Fish to New Fish Tank?

There are 2 reasons why you have to wait before adding fish to your new tank. The first reason is you need to give your aquarium time to become balanced. The nitrogen cycle needs to get established. This usually takes at least 3 weeks.

The second reason why you need to wait before you add fish to your new tank is you want your aquarium plants to grow and take hold. Waiting for your plants to take hold will prevent your plants from getting uprooted by fish.

When to Add Fish to New Fish Tank?

The good news, you don’t need to wait 3 weeks to add the first fish to your new tank! Let the aquarium cycle for a week. You can add your first fish after 1 week.

By adding at least one fish, you are actually helping your new tank get established because the waste produced by that fish is needed for the aquarium to cycle properly. After all, it’s pointless to let your aquarium cycle with just plain water, you need waste for nitrogen cycle and good bacteria to establish itself.

How to Add Fish in Batches to New Fish Tank

The key is to introduce fish to your new tank in batches. By adding fish in batches, you are helping the more timid and small fish get acclimated to its new fish tank. It will also help space out the bioload so you don’t strain your new aquarium system too much.

1. Add Algae Eater

After the first week, add a hardy, algae eater like an Otocinclus – also known as“Otos” or “dwarf suckers. The good bacteria needed to keep your fish tank healthy will establish itself in the filter media.

In my son’s 10 gallon fish tank, we added 2 Midget Sucker Catfish (Otocinclus affinis). It’s a small algae eater growing to only 1.5 inches.

2. Add Small and Shy Fish

Two weeks after adding your algae eater, add small and timid fish into your new tank. This will help shy fish get acclimated to the new fish tank.

In my son’s 10 gallon fish tank, we added the guppies (although not shy, they are probably the less aggressive of my son’s livebearer tank).

3. Add Larger and Active Fish

Two weeks after adding the small and shy fish, add the larger and more active fish into the new tank.

After letting the guppies get acclimated for 2 weeks, we then added the swordtails into my son’s 10 gallon fish tank. Compared to guppies, swordtails are more aggressive that’s why we introduced fish into the new fish tank in this order.

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