How to lower nitrate in your aquarium

Why nitrate matters

Nitrate is the end product of the nitrogen cycle. In small amounts it’s usually fine; in high amounts it stresses fish, encourages algae, and can affect growth and health. Many keepers aim for under 20 ppm (some under 10). Test regularly so you see the trend — App-aquatic can log your readings so you know when nitrate is creeping up.

Water changes

The most reliable way to lower nitrate is to remove water and replace it with clean, dechlorinated water. A 25–50% change dilutes nitrate immediately. Do it weekly or more often if nitrate stays high. See our how often to change water guide for a schedule that fits your tank.

Feed less, clean more

Overfeeding adds waste and pushes nitrate up. Feed only what fish eat in a minute or two; remove uneaten food. Vacuum the substrate when you do water changes so debris and mulm don’t break down in the tank. Good maintenance is half the battle.

Plants

Live plants use nitrate as fertiliser. Fast-growing or floating plants (e.g. hornwort, water sprite, java fern) can help keep nitrate lower in a planted tank. They’re not a replacement for water changes but they add a buffer. See best plants for beginners if you’re new to plants.

Stocking and filtration

Overstocked tanks produce more waste and nitrate. Stay within a sensible bioload (see overstocking). A filter that’s adequate for the tank size helps; it doesn’t remove nitrate by itself, but it keeps the system healthy so water changes do the rest.

Quick takeaways

• Water changes are the main way to lower nitrate. Do them regularly.
• Feed sparingly, vacuum substrate, and avoid overstocking.
• Plants can help; track nitrate so you spot a rise before it gets high.