Nitrate

Nitrogen compound (NO₃⁻) — the end product of the nitrogen cycle. Far less toxic than ammonia or nitrite. Removed primarily by water changes and live plants. Conservative target: under 40 ppm.

Nitrate is the relatively-safe endpoint of the nitrogen cycle. Unlike ammonia and nitrite, it accumulates over time in the water column rather than being consumed by tank bacteria (anaerobic denitrification can remove it, but is uncommon in standard freshwater setups).

The two ways to remove nitrate: 1. Water changes — replace ~25-30% of tank water weekly with dechlorinated tap water at similar temperature. This is the standard hobby method. 2. Live plants — actively absorb nitrate as a nutrient. Heavily planted tanks can run with very little nitrate buildup.

Nitrate tolerance varies by species. Most community fish tolerate up to ~40-50 ppm without issue, but breeding success and long-term health are better at <20 ppm. Sensitive species (discus, shrimp, ottocinclus) prefer <10 ppm.

Beginner-safe rule

Beginner-safe rule: test nitrate weekly. If it climbs above 40 ppm, do a 30-50% water change. If it climbs back fast, your tank is overstocked or underplanted.