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Cycle Coach
Cycling a new saltwater tank is a waiting game with three stages — and it's genuinely hard to tell where you are. Log each water test and the coach tells you which stage you're in, exactly what to do next, when to test again, and the day it's finally safe to add your cleanup crew and first fish. Set a test reminder so you never lose track. Your log saves right here in this browser.
Taking a while? Speed it up — and why cycles stall
- Seed it with live biology. Cured live rock, live sand, or a bottled marine nitrifying-bacteria starter is the real accelerator — a tank started on dry rock from scratch is the slowest.
- Keep it warm and running. Hold about 24–27 °C with the heater and flow on; nitrifiers establish faster in warm, oxygenated water.
- Keep alkalinity up. The bacteria slow right down in low-alk, low-pH water — keep alkalinity in a normal reef range (about 8–12 dKH).
- Feed them steadily. Hold the ammonia around 2 ppm — too little starves the colony, over ~5 ppm stalls it. Don't do water changes or run the skimmer wet mid-cycle.
- Alkalinity/pH dropped. The most common marine stall — check your alkalinity if the numbers stop moving.
- Dry rock, no seed. With no starting bacteria a cycle can crawl for weeks; add live rock/sand or a bacteria starter.
- Tap water instead of RO/DI. Chlorine/chloramine and contaminants stall or poison the cycle — mix salt with RO/DI water.
- Ammonia too high. Over ~5 ppm inhibits the bacteria — dilute with a matched-salinity water change back toward 2 ppm. Too cold or no flow stalls it too.
Cycling questions
How long does it take to cycle a saltwater tank?
Usually two to six weeks, but it varies a lot with how you start it. Cured live rock and a bottled-bacteria dose can shorten it; dry rock started from scratch takes longer. The clock does not matter as much as the test result: you are cycled when the tank turns a ~2 ppm ammonia dose into 0 ammonia and 0 nitrite within 24 hours.
How do I cycle a reef tank without fish?
Fishless is the recommended way. Add an ammonia source (a bottle of pure ammonia, or the die-off from uncured live rock) so the bacteria have food, dose a bottled nitrifying-bacteria starter if you like, and test every few days. Never cycle with fish as the ammonia source - it is stressful and often fatal, and it is unnecessary.
When can I add fish and coral after cycling?
Once ammonia and nitrite both read 0 and nitrate is present, do a large water change to bring the nitrate down, then add your cleanup crew and a single hardy fish first - a few at a time, never all at once. Corals come later, after the tank has matured and parameters are stable. This tracker flags the completion test and the water-change step.
Where is my cycling log stored?
Only in your own browser (via localStorage) — your readings stay in your hands. Nothing is uploaded and there is no account. The trade-off is that the log lives on this device and browser, so clearing your browser data will erase it.
Why is my saltwater cycle stuck or taking so long?
The most common marine stall is low alkalinity or pH — nitrifying bacteria slow right down in low-alk water, so check your alkalinity (aim for a normal reef range, about 8–12 dKH) if the numbers stop moving. Other stalls: starting on dry rock with no live seed (the cycle can crawl for weeks — add live rock/sand or a bottled bacteria starter), mixing salt with tap water instead of RO/DI, a tank that is too cold or has no flow, or an ammonia level over about 5 ppm, which inhibits the bacteria (dilute it back toward 2 ppm with a matched-salinity water change). To speed a cycle up, seed it with live biology, keep it warm (about 24–27 °C) and running, and hold the ammonia around 2 ppm.