New tank syndrome calculator

Umbrella name for the toxic ammonia + nitrite spike that hits any new aquarium before the bacterial colony establishes. The cycle has two stages: first-stage bacteria (Nitrosomonas) convert ammonia to nitrite — usually online by day 7-14. Second-stage bacteria (Nitrospira) convert nitrite to nitrate — usually online by day 21-28. Until both colonies are running, ammonia and/or nitrite accumulate. The total cycle takes 4-6 weeks without seeded media. Heavy plant stocking shaves about a week off by consuming ammonia directly.

It reads the pattern of your three test results: ammonia + nitrite + nitrate. Pre-cycle = brand-new tank, no readings yet. Ammonia-spike = ammonia present, nitrite ≈ 0, nitrate ≈ 0 (first-stage bacteria still building). Nitrite-spike = nitrite present (first-stage done, second-stage building). Near-cycled = ammonia 0 or trace, nitrite low + dropping, nitrate present. Cycled = ammonia 0, nitrite 0, nitrate present. The stage tells you what to expect next; the days-since-setup gives a rough completion estimate based on the standard 4-6 week timeline.

No, mostly. Fishless cycling intentionally holds ammonia in the 1-4 ppm range — that's the bacterial food. Water changes lower the ammonia and slow the colony build. The exception: ammonia above ~5 ppm starts inhibiting Nitrosomonas, so a 25-30% change to bring it back into range is appropriate. Same for nitrite above ~5 ppm during the second-stage spike. Otherwise: leave it alone, dose more ammonia when readings drop to zero, and let the bacteria do their work. The calculator handles fishless mode by skipping water-change recommendations unless levels enter the inhibitory range.

If you're already in fish-in mode (fish present from day 1), you're committed — the action is to keep ammonia and nitrite under 0.25 ppm with daily water changes + Prime dosing. If you're fishless cycling and considering adding fish before completion: don't. Adding fish to a tank with detectable ammonia or nitrite is the most common cause of new-tank fish loss. Wait for the cycled signature (ammonia 0, nitrite 0, nitrate present), then add 1-2 small fish per week to give the colony time to scale to the new bioload.

Plants consume ammonia and nitrate directly through their roots and leaves — they don't care about the bacterial pathway. A heavily planted tank pulls ammonia out of the water before Nitrosomonas can convert it, which softens the visible spike and reduces the bioload the bacterial colony needs to scale to. The tank still cycles (you still need both bacterial colonies for long-term stability), but the path is gentler and the timeline is roughly a week shorter. The calculator shifts the estimated cycle length from 35 to 28 days when the heavy-plants toggle is on.

A stuck cycle. Common culprits: pH below 7.0 (Nitrosomonas growth slows noticeably below 7, and is documented to stop below ~6), temperature below 70°F (bacterial growth is temperature-dependent — aim for 75-80°F during cycling), zero KH (the bacterial process consumes alkalinity; zero buffer means pH crashes and stalls the cycle), or insufficient ammonia source for fishless cycling. Test pH and KH; if pH is low, raise it gradually with crushed coral in the filter or a small KH addition. If you're fishless cycling without a proper ammonia source (Dr Tim's ammonium chloride or fish food decomposition), the bacteria starve.