Why it matters
Chronic nitrate above range fuels algae, suppresses coral growth, and slowly stresses fish. Sudden changes from large water changes can shock livestock.
Ideal ranges
| Water type | Ideal | Acceptable |
|---|---|---|
| Freshwater community | below 20 | below 40 |
| Planted tank | 10 to 20 | — |
| Reef tank | 1 to 10 | — |
| Fish-only saltwater | below 20 | — |
| Koi pond | below 40 | — |
- Reef tank: Zero nitrate starves coral zooxanthellae.
How to test
- 1
Use a liquid test kit
Salifert and Red Sea read low ranges accurately for reef. API is fine for freshwater.
- 2
Shake bottle 2 vigorously
API nitrate kit reagent settles. Skipping the shake gives false low readings.
How to correct high nitrate
Larger or more frequent water changes
25 percent weekly is the baseline. Increase frequency before increasing volume to avoid shock.
Add fast-growing plants or refugium macroalgae
Pothos, hornwort, chaeto, and caulerpa pull nitrate out as they grow.
Reduce feeding and stocking
Most nitrate problems trace back to overfeeding or overstocking.
Reef: dose carbon source carefully
Vinegar, vodka, or NoPoX feed bacteria that strip nitrate. Start at 10 percent of label dose.
How to correct low nitrate
Reef only: dose nitrate or feed more
Coral browning and pale tissue often mean nutrient starvation. Dose Brightwell NeoNitro or feed an extra cube of mysis daily.
Common causes
- •Overfeeding
- •Overstocking
- •Insufficient water changes
- •Tap water with high nitrate (test source water)
FAQs
My tap water has 20 ppm nitrate. What do I do?
Use an RO unit, mix RO with tap to dilute, or polish water through a nitrate-removal resin like Seachem Matrix Carbon.