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Water quality and maintenance

How to Cycle a Betta Tank: Fishless Cycling Step by Step

Fishless cycling explained in order: what to dose, what to test, what each reading means, and how to tell when the tank is genuinely ready for a betta.

By Published 4 min read
A sponge filter releasing bubbles in an empty planted aquarium during fishless cycling
The filter stays running while the tank cyclesIllustrative close view of the filter and water movement in an empty cycling aquarium. No test result or bacterial growth is being depicted.Illustration

Cycling is the step retail never mentions, and it is the one that decides whether your fish lives out its three to five years or dies in six weeks.

It is also boring. You will spend a month looking at an empty tank and testing water. That is the whole trick.

What cycling actually is

Your fish excretes ammonia continuously. Uneaten food produces more.

Two groups of bacteria handle it. The first converts ammonia to nitrite. The second converts nitrite to nitrate. Both are toxic; nitrate is far less so, and you remove it with water changes.

Cycling means growing those colonies before a fish depends on them. They live mostly in your filter and substrate, not in the water, which is why rinsing filter media under a tap sets you back to the beginning.

A circular diagram showing a fishless ammonia source becoming ammonia, nitrite and then nitrate
  1. Ammonia source
  2. Ammonia
  3. Nitrite
  4. Nitrate
The two bacterial conversions that matterA fishless ammonia source produces ammonia. One bacterial group converts it to nitrite, then another converts nitrite to nitrate.Diagram

What you need

  • The tank, set up and running, with heater and filter on
  • A liquid test kit that reads ammonia, nitrite and nitrate
  • An ammonia source: bottled pure ammonia, or fish food
  • Dechlorinator
  • Patience, which is the part people skip

Bottled bacteria are optional. Some products shorten the process noticeably and some do almost nothing, so treat any of them as a possible head start rather than a replacement for testing.

The process

1. Get the tank warm and running

Bacteria establish faster in warm water. Set the heater to your normal target of 25 to 28 °C and leave the filter running the whole time.

Never let the filter stop for long during cycling. The colony lives in there and needs flow.

2. Add ammonia

With bottled ammonia, dose to roughly 2 ppm and test to confirm you hit it. Higher is not faster, and very high doses can stall the bacteria.

With fish food, add a small pinch and let it break down. That is slower and harder to control, but it works and costs nothing.

3. Test every day or two, and write it down

You are watching for a sequence, not a single number.

Stage Ammonia Nitrite Nitrate
Nothing started high 0 0
First colony working falling rising 0
Second colony working 0 falling rising
Cycled 0 0 present

A written log is genuinely useful here. Cycles stall, and a log shows you whether you are stuck or simply mid-way.

4. Keep feeding the colony

Each time ammonia hits zero, dose again to about 2 ppm. A colony with nothing to process starts dying back, and you lose progress.

5. Confirm it, twice

The tank is cycled when a fresh dose of ammonia reads zero ammonia and zero nitrite within about 24 hours.

Do that twice before trusting it. One clean result can be luck or a mis-read vial.

6. Water change, then the fish

Nitrate will be high after a month of dosing. Do a large water change to bring it under about 20 ppm, match the temperature, then add your betta.

How long it takes

Three to six weeks is normal without a bacterial supplement. Two weeks happens. So does eight.

Cold water is the most common cause of a slow cycle: below about 21 °C the bacteria barely work. After that it is usually a missing ammonia source, so the colony has nothing to grow on, or chlorinated water added without conditioner, which kills what has grown so far.

Two less obvious ones. Dosing ammonia much above 5 ppm can stall the process rather than speed it up. And cleaning the filter during cycling removes the colony you are trying to establish, so leave it alone until the tank is finished.

The zero-readings trap

A brand new tank reading zero ammonia, zero nitrite and zero nitrate is not clean. It is almost always a tank where nothing has begun.

A cycled tank produces nitrate. If nitrate is absent, the second conversion is not happening, so there is nothing there to protect a fish.

If the fish is already in the tank

Most people arrive here having bought the fish first. It is recoverable.

  1. Test daily. Ammonia and nitrite are what you are watching.
  2. Change water whenever either reads above 0.25 ppm, 25 to 50 percent, dechlorinated and temperature matched.
  3. Feed lightly, because every uneaten pellet becomes more ammonia.
  4. Leave the filter alone. Whatever colony exists is in there.
  5. Keep going until both hold at zero between changes.

This takes longer than a fishless cycle because you are removing the very ammonia the bacteria need. That trade is worth it: the fish comes first.

You are not doing anything wrong by being in this position. Almost every keeper starts here, because the fish and the tank are sold together with no mention of what has to happen between them.

Where to go next

Once the tank holds at zero on its own, the weekly routine is what keeps it there, and the numbers are what you check it against.

Key takeaways

  • Cycling grows the bacteria that convert ammonia to nitrite and then to nitrate. Without them, waste accumulates and burns the fish.
  • A tank is cycled when it clears a dose of ammonia to zero ammonia and zero nitrite within about 24 hours. The calendar does not decide it.
  • Expect three to six weeks. Bottled bacteria can shorten that, but you confirm with a test rather than with the label.
  • Zero readings across the board on a new tank usually mean nothing has started yet, not that the water is clean.
  • If the fish is already home, cycle around him with daily testing and frequent partial water changes.

Frequently asked questions

How long does it take to cycle a betta tank?
Usually three to six weeks. It finishes when the tank converts a fresh dose of ammonia to zero ammonia and zero nitrite within about 24 hours, and that is the only thing that decides it. A tank can look finished at two weeks and stall for another three.
Can I cycle a tank with the betta already in it?
Yes, and many people have to. Test daily, change 25 to 50 percent of the water whenever ammonia or nitrite reads above 0.25 ppm, and feed lightly. It is slower and harder on the fish than cycling empty, but it works and it is recoverable.
Do bacteria in a bottle actually work?
Some products genuinely shorten the cycle, and some do very little. Treat any of them as a possible head start rather than an instant fix, and confirm with your test kit before adding a fish. The label is not evidence.
Why is my ammonia not dropping?
Common causes are temperature too low, no ammonia source to feed the colony, chlorinated water added without conditioner, or dosing ammonia so high that it stalls the bacteria. Keep the tank warm, keep dosing modestly, and be patient.
All my readings are zero on a brand new tank. Is it cycled?
Almost certainly not. A cycled tank produces nitrate, so zero nitrate alongside zero ammonia usually means the cycle has not started. Add an ammonia source and watch whether the tank processes it.
Should I change water while cycling?
Not routinely, because you are feeding a bacterial colony rather than keeping a fish. The exception is nitrite so high it goes off the top of the chart, which can stall the cycle. Then change enough to bring it back onto the scale.

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