Guide 32 — Troubleshooting Guide

Ammonia & Nitrite Spikes: What To Do

Our Water Testing 101 guide covers what to test for. This one is about the moment a test actually comes back bad — what a reading means, what to do in the next hour, and what to avoid doing when a shrimp or snail tank is involved.

What a Reading Actually Means

In a fully cycled, established tank, ammonia and nitrite should both read zero on a test kit — not "low," zero. Our Nitrogen Cycle guide covers why that's the baseline: beneficial bacteria convert ammonia to nitrite and then nitrite to the far less harmful nitrate, and in a mature tank that conversion keeps pace with what's being produced. Any detectable ammonia or nitrite in an established tank means something has outpaced the bacteria — not that a small amount is normal background noise.

Even a low reading is worth acting on quickly. Ammonia is measurably harmful to aquatic life at concentrations as low as 1ppm, and invertebrates in particular have very little tolerance for it — by the time a reading shows clearly on a test kit, exposure has often already been happening for some time.

Immediate Steps

The response to a spike is largely the same whether it's ammonia or nitrite, and speed matters more than precision. In order:

• —  Stop feeding. Uneaten food and waste are the raw material for ammonia. Pausing feeding for a day or two removes one of the inputs while you deal with the rest.
• —  Do a substantial water change. A 25-50% change with dechlorinated, temperature-matched water immediately dilutes whatever's in the tank. Don't be afraid of a bigger change than usual — the risk from ammonia or nitrite exposure is greater than the risk from a large, well-matched water change.
• —  Increase surface agitation or aeration. More oxygen in the water supports both your livestock and the bacteria working to process the spike, and helps if a large water change has temporarily disturbed the biofilter.
• —  Retest daily until both read zero. Don't assume one water change has fixed it — keep testing and repeating water changes until the readings hold at zero on their own, which tells you the bacterial colony has caught back up rather than you're just diluting a problem that's still being produced.

Working Out Why It Happened

Fixing the immediate spike matters, but a spike in an established tank is a symptom, not a random event. The most common causes are overfeeding, a sudden increase in bioload (new stock added faster than the colony can adjust to), a dead animal or plant matter decaying unnoticed, over-cleaning or replacing filter media all at once and wiping out too much of the bacterial colony, or a tank that was never fully cycled in the first place before livestock went in.

Go through the tank methodically: check for anything dead or decaying, review recent feeding amounts, confirm nothing was added to the filter or gravel that disrupted the bacteria, and check whether new livestock was introduced without appropriate quarantine or acclimation. Identifying the cause is the only way to stop it happening again — repeated water changes without addressing the underlying trigger just delays the next spike.

Watching Your Livestock During Recovery

While the tank recovers, watch behaviour closely. Snails may retreat into their shells or become unusually inactive. Shrimp under ammonia or nitrite stress often show erratic swimming, hover near the surface or filter outflow where oxygen is highest, or become lethargic and pale. These are signs of ongoing stress even after a water change has brought the numbers down, and are worth continuing to monitor for a few days rather than assuming recovery the moment the test kit reads better.