Ammonia

Ammonia is the first and most critical parameter you should monitor in any aquarium, whether freshwater or saltwater. Even slight elevations can be deadly. In both water types, anything above 0.5 ppm is dangerous, but in saltwater, ammonia is approximately 10 times more toxic than it is in freshwater. That means any detectable ammonia in a saltwater tank is a serious concern.

If your test kit doesn’t show a bright neon yellow (for strips) or exactly 0 ppm (for liquid tests), it’s time to act. In a fully cycled and stable system, ammonia should always be undetectable—even though trace amounts might be present, they should never register on a test.

False Positives in Freshwater

It’s worth noting that many liquid test kits commonly show a false positive at 0.25 ppm in freshwater tanks. If you’re not seeing any stress in your fish, and nitrites are at zero, it’s likely a harmless reading. Saltwater test kits tend to be more precise, and color changes are easier to interpret, so assume any detectable ammonia in saltwater is a real problem.

Fixing Ammonia Issues

There are two main approaches to dealing with ammonia:

1. Perform a Water Change

   • A 50% water change is the fastest and most effective way to immediately reduce ammonia levels. This cuts the concentration in half, potentially saving your fish. If levels remain high, daily water changes may be necessary until the issue is resolved.

2. Restore Your Filter's Biological Capacity

   • If ammonia is building up, it means your filter isn’t processing waste correctly. Ask yourself:

     • Is the filter too new?

     • Was the media recently changed or rinsed improperly?

     • Is the cartridge clogged or missing?

   • The best fix is to reseed the filter with live bacteria, either from an established tank’s filter media or clean, pesticide-free soil. Yes, garden soil—if free from additives—contains the same types of bacteria that establish a healthy nitrogen cycle in aquariums. Just a small amount placed directly in the filter can jump-start the bacterial colonies.

Ammonia Poisoning: Damage and Recovery

Acute ammonia poisoning is often reversible—if caught early and addressed quickly, most fish will recover once removed from contaminated water or after ammonia is neutralized. However, chronic exposure or extremely high concentrations can cause lasting damage or death.

Keeping ammonia at zero starts with a cycled, mature filter. It’s not optional—it’s essential for the long-term health of your aquatic life.