Nitrogen for Aquarium Plants: Nitrate, Deficiency and Dosing
Fish keepers are told to keep nitrate low. Plant keepers often need to add it. Here’s how to get the balance right.
Nitrogen is the nutrient plants use most. It builds proteins, chlorophyll and new leaves. In a fish-only tank, nitrate is a waste product you remove with water changes. In a planted tank it’s food, and a well-planted tank can use it up faster than fish produce it.
Where aquarium plants get nitrogen
Plants take nitrogen as ammonium and as nitrate. Fish waste and leftover food break down into ammonia, which bacteria turn into nitrate. In a lightly planted tank with lots of fish, that’s often enough. In a densely planted tank, especially with good light or CO₂, plants use it all and growth stalls.
That’s why the PPS-Pro macro bottle includes potassium nitrate. It supplies a steady, small amount of nitrate every day, alongside potassium.
Signs of nitrogen deficiency
- Older, lower leaves fading evenly to pale green then yellow, veins included
- Small new leaves and short, thin stems
- Red plants turning very red but growing slowly and stunted
- A nitrate test reading close to zero in a planted tank
Even yellowing of whole older leaves is the key difference from magnesium, where the veins stay green. See our guide to aquarium plant leaves turning yellow for help telling them apart.
| Nitrate test | What it means for plants |
|---|---|
| 0 to 5 ppm | Likely too low for a planted tank. Plants may starve |
| 5 to 20 ppm | A comfortable range for most planted tanks |
| 20 to 40 ppm | Plenty. Fine for plants and most fish |
| Over 40 ppm | More than plants need. Do a water change |
Is fish waste enough?
Sometimes. A slow, low-light tank full of fish may never need extra nitrogen. A well-planted tank with stem plants, a carpet or injected CO₂ almost always does. If your nitrate test sits near zero and older leaves are fading, plants are telling you they want more.
How to dose nitrogen
Dose a balanced macro solution daily rather than big amounts once a week. Small daily doses keep nitrate steady, which plants prefer and algae don’t. With PPS-Pro, 1ml per 10 litres of the macro bottle each day is the starting point. Our dosing guide explains how to adjust for your tank.
Advice to keep nitrate at zero comes from fish-only tanks. Plants need a little nitrate in the water all the time. Aim for a steady, moderate reading and keep up regular water changes.
Too much nitrogen and algae
Nitrate on its own rarely causes algae. Algae takes off when nutrients, light and CO₂ are out of balance. Keep your doses steady, match them to your light and keep the tank clean. Read more in why you keep getting algae in your planted tank.
Quick answers
Do aquarium plants need nitrate?
Yes. Nitrate is one of the main ways plants take in nitrogen, which they use to build new leaves and stems.
What is a good nitrate level for a planted aquarium?
Around 5 to 20 ppm suits most planted tanks. Close to zero is usually too low for plants.
What does nitrogen deficiency look like in aquarium plants?
Older leaves fade evenly to yellow, veins included, and new growth is small and slow.
Is fish waste enough fertiliser for aquarium plants?
In lightly planted, low-light tanks it can be. Densely planted or high-light tanks usually need extra nitrogen and potassium.
Products mentioned in this guide
The main source of nitrogen and potassium in your macro bottle. Usually the first compound to run low.
Best valueEverything to start dosing on day one: pre-measured macro and micro compounds, two 500ml bottles, two dosing syringes and a full dosing guide.
Easiest startBoth bottles already mixed for you. Shake, measure 1ml per 10 litres and dose. No scales, no spoons.
Copper-free aquarium plant food.
Dose on day one.
Pre-measured compounds, bottles, syringes and a full dosing guide. Shrimp safe, made in the UK, free UK delivery on every order.
Everything you need to get the most from your planted aquarium.
