Is my tank ready for fish?

Log your water tests. CycleCheck tells you where your tank is in the nitrogen cycle and what to do next.
A few quick questions about your tank
4 of 5
01
Does the tank have live plants?
Fast-growing plants take up ammonia too.
02
Did you add bottled bacteria?
A starter culture sold in bottles.
03
Is there chloramine in your tap water?
Your water supplier can tell you. Many cities use it.
04
Are fish already in the tank?
Then the advice switches to keeping them safe.
05
How big is the tank?
Used to work out the ammonia dose.
The answers change the advice. You can edit them later.

Cycle tracker

settings

What the tracker does

You test your water with an ordinary kit and tap the numbers you see. CycleCheck works out which stage of the nitrogen cycle your tank is in and gives you one clear next step: add ammonia, wait, change some water or run the 24-hour test. It also tells you why, so you learn as you go.
Your tests stay in your browser: there is no account, and the values you enter are never sent anywhere. Save a backup file now and then, and you can move your log to another device.

The nitrogen cycle in plain words

Fish waste and leftover food release ammonia, and ammonia harms fish even in small amounts. Bacteria that settle in the filter turn it into nitrite, which is also harmful. A second group of bacteria turns nitrite into nitrate, which is much milder and leaves the tank with regular water changes.
Cycling a new tank means growing both groups before the fish arrive. You feed the bacteria with ammonia and watch three numbers — ammonia, nitrite and nitrate — change over 4 to 8 weeks.

The stages you will see

  • 1.
    Not started. Ammonia, nitrite and nitrate are all near zero. Add an ammonia source to about 2 ppm.
  • 2.
    Stage 1, ammonia. Ammonia is there, nitrite is not. The first bacteria are still growing. Top ammonia back up to 2 ppm whenever it falls below 1 ppm.
  • 3.
    Stage 2, nitrite. Nitrite appears, which means the first bacteria work. Keep feeding ammonia. If nitrite reaches 5 ppm or more, change some water and pause the ammonia until it drops.
  • 4.
    Stage 3, almost there. Nitrite falls, nitrate rises and ammonia disappears quickly.
  • 5.
    Cycled. After a full dose, ammonia and nitrite read 0 a day later, twice in a row. Do a big water change to bring nitrate to 30 ppm or lower, then add fish.

What it keeps an eye on

  • Fish already in the tank. If ammonia or nitrite reaches 0.25 ppm, a red warning tells you what to do right away.
  • A stalled cycle. When readings barely move for 7 days, you get a checklist of the usual causes, such as low pH, cold water or untreated tap water.
  • A possible setback. If the tank used to clear ammonia within a day and the numbers climb again, you get the common causes to check.
  • Doubtful readings. For example, nitrate showing up before any nitrite, with tips for rechecking the test.

A helpful hint, not a vet

CycleCheck follows the usual rules for cycling a tank with ammonia and explains every step, but it cannot see your tank. If your fish look unwell, ask a good local fish shop or an aquatic vet.