How to Lower Nitrate in Your Aquarium
6 min read · TankBase
High nitrate is the most common water-quality problem in home aquariums. It stunts fish growth, fuels nuisance algae and bleaches coral colour. The good news: it's one of the easiest parameters to control once you know what's driving it.
Why your nitrate is climbing
Overfeeding — uneaten food rots and the bacteria turn it into nitrate.
Overstocking — too many fish producing waste for the tank size.
Infrequent water changes — nitrate accumulates because nothing is removing it.
Clogged mechanical filtration — trapped detritus continually breaks down into ammonia → nitrite → nitrate.
The fastest safe way to bring it down
Do a 25% water change with fresh dechlorinated water (or fresh saltwater at the same SG).
Wait 24 hours, retest. Repeat the 25% change up to 3 times across a week. Never do more than 30% in one go — it can shock fish and corals.
Clean the filter sponge in old tank water (never tap water) and remove visible detritus from the substrate with a gravel vacuum.
Keep it down long-term
Feed less. Adult fish only need feeding once a day, and only what they finish in 30 seconds.
Add live plants (freshwater) or macroalgae in a refugium (marine) — both consume nitrate directly.
Schedule a 10–15% water change weekly. A consistent small change beats a panicked big one.
Track every reading in TankBase Tank Log so you can spot the trend before it becomes a problem.
Target ranges
Reef tank: 1–10 ppm for SPS, 5–25 ppm for mixed reef and LPS.
Freshwater community: under 40 ppm.
Planted tank: 10–20 ppm — plants need some nitrate as fertiliser.
Track these parameters automatically
TankBase Tank Log charts every reading you take and flags anything out of range — free to try.
Open Tank Log →