Setup path, stage 6
How to cycle a reef tank, and how to prove it is done
Bottled bacteria labels promise a cycle in days. Some are right for some tanks. The only way to know is a test you can do at home: dose ammonia, wait 24 hours, and see where it went.
Last checked . How we check
What do you need for this stage?
- Ammonia and nitrite test kits (nitrate too)
- An ammonia source: ammonium chloride is easiest to measure
- Bottled nitrifying bacteria (optional, saves weeks)
- A notebook or the checklist below for daily readings
What does cycling actually do?
Fish and food make ammonia. Bacteria on the rock turn ammonia into nitrite, and other bacteria turn nitrite into nitrate, which is far less harmful. A new tank has too few of both. Cycling grows them by feeding them ammonia until they can clear a full day's load in a day.
Is my tank cycled? What each brand claims, and the test that proves it
| Product or source | What it says | Timing claimed | What proves it at home |
|---|---|---|---|
| Fritz TurboStart 900 | Dose and stock right away (label, read via retailers) | Five days or less | The 24-hour ammonia test below. The label gives no follow-up test. |
| Seachem Stability | Dose daily for seven days, fish can go in at any time (label, read via retailers) | Seven days | The 24-hour ammonia test before fish, and daily ammonia and nitrite for two weeks after. |
| Red Sea Reef Mature | A four-bottle programme, then ready to stock including SPS (manual, search summary) | 21 days | The 24-hour test, then the coral gate in stage 10. Its programme page gives no timeline. |
| Dr Tim's recipe (BRS) | Bacteria plus ammonium chloride to 2 ppm | Usually 1 to 2 weeks | Its own test: re-dose to 2 ppm, ready if ammonia is under 0.2 ppm within 24 hours. |
| BRS 5 Minute Guide | Hardy fish plus live bacteria | Weeks | Ammonia zero for two to three weeks in a row, nitrite zero, nitrate appearing. |
| Charterhouse | Fish food or an ammonia source | "Several weeks" | Ammonia and nitrite zero, nitrate low. |
| Dry rock, no bottled bacteria | Dose ammonia and wait (keepers) | About 4 to 8 weeks (typical) | The 24-hour test. |
How do I do a fishless cycle with bottled bacteria?
- Hold the tank at about 24 to 25.5 C (Dr Tim's gives 75 to 78 F).
- Switch off UV, ozone and the skimmer, and take out filter socks, for 48 hours after adding bacteria.
- Work out the dose on the net water volume: Dr Tim's takes about 20% off for rock and sand.
- Add the bacteria, then ammonium chloride to about 2 ppm. Never go above 5 ppm.
- Test ammonia and nitrite daily. When ammonia falls below about 0.5 ppm, top it back to 2 ppm.
- When the 24-hour test passes twice, test nitrate. If it is high from all the dosing, do a large water change before any animals go in.
Keep lights off or low while there is nothing to light. Algae grow on the ammonia and nitrate too.
Should I cycle with fish?
BRS describes cycling with a few hardy fish and live bacteria, testing ammonia and doing water changes when it rises. It works when done carefully, but it exposes fish to ammonia and nitrite that a fishless cycle avoids, and it leaves you with no option to treat a sick fish without harming the cycle. We do not recommend it.
What are the steps, in order?
- Confirm salinity and temperature are at target.
- Add bottled bacteria (if using) and ammonia to 2 ppm.
- Test ammonia and nitrite every day and write the numbers down.
- Re-dose to 2 ppm when ammonia drops.
- Run the 24-hour test; pass it twice.
- Test nitrate; water change if it is high.
Your checklist
Tick items as you go. Ticks are saved in this browser only and fill the depth gauge.
0 of 6 done for stage 6. Saved in this browser only.
What test must pass before moving on?
Your tank is cycled when, twice, a day apart:
- Ammonia dosed to 2 ppm falls to 0.25 ppm or less within 24 hours.
- Nitrite is 0.25 ppm or less at the same reading, ideally zero.
- Nitrate is present (proof the second step works), and you have reduced it with a water change if it is very high.
What are the common mistakes?
- Stocking on the label date without testing.
- Dosing ammonia above 5 ppm, which can stall the bacteria.
- Leaving the skimmer or UV running straight after adding bottled bacteria.
- Reading the colour chart under a warm room light.
- Adding live rock after the cycle.
- Treating a cycled tank as ready for corals.
Where do sources disagree?
| Topic | What sources say | Our reading |
|---|---|---|
| How long a cycle takes |
| Each is right for some tanks. The 24-hour test tells you which yours is. |
| Does nitrate appearing prove the cycle? |
| Nitrate shows the second step has started. Wait for nitrite to clear as well. |
| Keep dosing ammonia? |
| Top up to 2 ppm, never above 5 ppm. |
| Fish-in or fishless |
| Fishless. |
Sources
- BRS, fishless cycling with ammonium chloride and bottled bacteria (Dr Tim’s recipe)
- BRS, 5 Minute Saltwater Aquarium Guide, episode 15: cycling
- Charterhouse Aquatics, how to set up a marine aquarium step by step
- Red Sea, Reef Mature first-cycle programme page
- Red Sea, Reef Mature starter kit manual
- Fritz Aquatics, FritzZyme TurboStart 900 (label claims read via retailer listings)
- Seachem, Stability (label claims read via retailer listings)
Figures from sources read as a search summary only are shown as typical figures: check them before you rely on them. Found a mistake? Tell us how to fix it.