Nitrate builds up naturally in any aquarium, but you can speed it up if your tank is too low

Nitrate rises on its own as fish waste and uneaten food break down in your tank. If your test shows nitrate below 5 ppm (parts per million), your tank is not cycling waste fast enough, or you are doing water changes too often. The fastest way to raise nitrate is to feed more, skip a water change, or add a source of decaying organic matter — but the real fix depends on why your nitrate is low in the first place.

Most aquariums sit between 20 and 40 ppm nitrate. Below 5 ppm usually means either the tank is brand new and still establishing bacteria, or you are removing nitrate faster than it builds up. Plants consume nitrate, so a heavily planted tank will run lower. Frequent large water changes also strip nitrate. If your fish and plants are healthy, low nitrate is not an emergency — but if you are trying to establish a cycle or support plant growth, you have several direct options.

Key Takeaways

  • Nitrate rises naturally from fish waste, but you can speed it up by feeding more often, reducing water change frequency, or adding decaying plant matter.
  • A new tank below 5 ppm nitrate is still cycling; this is normal and takes two to four weeks to stabilize on its own.
  • Plants and frequent water changes both remove nitrate, so lowering either one will let levels climb.
  • If you add organic matter to raise nitrate, monitor ammonia and nitrite daily because decomposition can spike those first.
  • Nitrate test kits measure in ppm and cost between $15 and $40; API and Tetra are the most common brands.

Feed more often and in larger amounts

Fish waste is the primary source of nitrate in any tank. More food means more waste, which means faster nitrate buildup. Increase feeding by one extra meal per day or add 25 percent more food to each meal. Watch the fish for signs they are actually eating it — uneaten food decays and can spike ammonia instead of nitrate, so only add what they finish in two to three minutes.

This method works fastest in tanks with fish that produce a lot of waste, like goldfish, plecos, or cichlids. In a tank with small fish like tetras or guppies, the effect is slower. If you overfeed and ammonia spikes, do a 25 percent water change when ready and cut back to normal feeding. Overfeeding also clouds water and promotes algae, so use this method only if your nitrate is genuinely low and your fish are healthy.

Reduce water change frequency or volume

Water changes remove nitrate along with other waste. If you are doing 50 percent changes weekly, drop to 25 percent weekly or skip one week entirely. This lets nitrate accumulate instead of being diluted out. The trade-off is that other waste products — ammonia and nitrite — will also rise, so test your water every few days while you adjust.

This approach works best if your tank is already stable and your fish are not stressed. In a new tank or one with high bioload (many fish in a small space), reducing water changes can cause ammonia or nitrite to spike dangerously. If that happens, go back to your normal schedule and use one of the other methods instead.

Add decaying plant matter or leaf litter

Dead leaves, driftwood, and plant stems decompose in the water and release nitrate as bacteria break them down. Add a handful of dried oak or almond leaves, a piece of decaying wood, or cut plant stems to the tank. These materials are sold as "Indian almond leaves" or "catappa leaves" at most aquarium stores for $5 to $12 per bag. They also lower pH slightly and release tannins that some fish prefer.

Watch ammonia and nitrite for the first week after adding organic matter. Decomposition can spike ammonia temporarily, especially in a small tank or one with weak filtration. If ammonia climbs above 0.5 ppm, remove the material and do a 25 percent water change. Once decomposition is underway, ammonia will drop and nitrate will rise steadily over two to three weeks.

Use a nitrate supplement if your tank is heavily planted

Planted tanks consume nitrate as fertilizer, so levels often stay below 5 ppm even in a mature tank. If you want to raise nitrate for plant growth, liquid fertilizers like Flourish Nitrogen or Thrive add nitrate directly. These cost $10 to $20 per bottle and last several months. Follow the dosing on the label — usually a few milliliters per 10 gallons weekly.

Dry fertilizers like Flourish Dry Macro also work and cost less per dose, but they require mixing and measuring powder. Test your nitrate weekly after dosing to avoid overshooting above 40 ppm, which can promote algae. If you are raising nitrate specifically to support plant growth, combine fertilizer with good lighting and CO2 injection for best results — nitrate alone will not fix slow plant growth if light is the real problem.

Check that your filter and bacteria are working

Nitrate is the end product of the nitrogen cycle: ammonia (from fish waste) converts to nitrite, then nitrite converts to nitrate. If your tank is more than four weeks old and nitrate is still below 5 ppm, your filter may not be running long enough, or the bacteria that produce nitrate may not be established yet. Run your filter 24 hours a day and test ammonia and nitrite — if either is above 0.5 ppm, the cycle is incomplete.

In a new tank, this is normal. Bacteria colonies take two to four weeks to mature. In an established tank, a spike in ammonia or nitrite means the filter is clogged, the media is old, or you have too many fish for the filter size. Clean the filter media in old tank water (not tap water, which kills bacteria) and test again in a few days. If ammonia or nitrite stays high, you may need a larger or second filter.

Test nitrate accurately with a liquid or digital kit

Nitrate test strips are cheap but unreliable — they often read low or high by 10 to 20 ppm. A liquid test kit like the API Master Test Kit ($25 to $35) is more accurate and includes tests for ammonia, nitrite, nitrate, and pH. Digital meters exist but cost $100 and up and require calibration. For most home aquariums, a liquid kit is the best balance of cost and accuracy.

Test your tank every three days while you are raising nitrate, and keep a log of the readings. Nitrate should climb slowly — 5 to 10 ppm per week is normal. If it jumps 20 ppm in a day, you have added too much organic matter or are overfeeding. Do a 25 percent water change and slow down. Once nitrate reaches 20 to 40 ppm, you can return to normal feeding and water changes.

Frequently Asked Questions

Is low nitrate bad for fish?

No. Fish do not need nitrate to survive — they need ammonia and nitrite to stay below 0.5 ppm. Nitrate below 5 ppm is not harmful. Low nitrate only matters if you are trying to grow plants or establish a new tank's cycle. If your fish are eating, active, and not gasping at the surface, low nitrate is not a problem.

Can nitrate get too high?

Yes. Nitrate above 80 ppm stresses fish and promotes algae blooms. Most aquariums should stay between 20 and 40 ppm. If your nitrate climbs above 60 ppm, do a 25 to 50 percent water change and reduce feeding or increase water change frequency. High nitrate is usually a sign you are overfeeding or not changing water often enough.

How long does it take to raise nitrate?

If you feed more and skip a water change, nitrate can rise 5 to 10 ppm in one week. Adding organic matter takes two to three weeks. In a new tank, nitrate may not appear at all for the first two weeks while bacteria are establishing. The speed depends on tank size, fish load, and filter strength.

Do plants really lower nitrate that much?

Yes. Fast-growing plants like water sprite, ludwigia, and stem plants consume nitrate as fertilizer and can keep levels below 5 ppm even in a mature tank. Slow-growing plants like anubias and java fern use less. If you have heavy plant growth and low nitrate, add a liquid fertilizer or reduce plant density if you want nitrate to rise.

What if ammonia spikes when I try to raise nitrate?

Stop whatever you added — remove organic matter, cut back feeding, or resume normal water changes. Do a 25 percent water change when ready and test ammonia again in 24 hours. Ammonia above 1 ppm can damage fish gills. Once ammonia is back below 0.5 ppm, try a gentler method, like feeding slightly more instead of adding leaves.