Knowledge Centre · Planted aquariums
Planted aquarium fertilising: macro and micronutrients explained
Fish waste alone rarely feeds a planted tank adequately, and "just add some fertiliser" glosses over a decision that's actually two separate questions: which nutrients your plants need, and whether they need feeding through the substrate, the water column, or both. This guide covers the macro and micronutrients plants actually use, root-feeding vs water-column feeding, the two main dosing philosophies (All-in-One and Estimative Index), and how fertilising connects to the light and CO2 you're already providing.
Before you choose a routine
This guide helps if…
You already have plants in, or are planning, a freshwater planted tank and want to understand what and how to feed them, beyond "add some fertiliser occasionally."
Look elsewhere first if…
Your plants already show a specific symptom — yellowing, holes, stunted new growth — our nutrient deficiency guide works from the symptom directly, rather than starting from general dosing theory.
Worth knowing: fertilising, light and CO2 work as a set. A dosing routine that's correct for a high-light, CO2-injected tank can be excessive for a low-tech setup with the same plants, and vice versa — match your routine to your actual light and CO2, not a generic schedule.
Macronutrients: nitrogen, phosphorus, potassium
Nitrogen, phosphorus and potassium (N-P-K) are needed in the largest quantities and are described as mobile within the plant — when supply is short, a plant can relocate them from older leaves to support new growth[1]. That's why deficiency in these nutrients typically shows first in older, lower leaves rather than new growth, a pattern covered in more detail in our nutrient deficiency guide. Nitrogen and phosphorus are also produced by the aquarium itself, from fish waste and decaying matter, so a stocked tank often needs proportionally less supplemental dosing of these two than an unstocked or lightly stocked one; potassium isn't meaningfully produced this way and generally needs deliberate dosing regardless of stocking.
Micronutrients: iron and trace elements
Iron, manganese, calcium, boron and other trace elements are needed in much smaller quantities but are generally described as immobile within the plant — a plant largely can't relocate them from old growth to feed new growth, so deficiency in these typically shows first in new leaves and growing tips rather than older ones[1]. Iron in particular is a common limiting factor in planted tanks, since it's needed for chlorophyll production and isn't reliably supplied by fish waste the way nitrogen and phosphorus partly are — most liquid fertilisers marketed for planted tanks include it specifically for this reason.
Root feeding vs water-column feeding
Not all plants take up nutrients the same way. Root-feeding species — Amazon sword and Cryptocoryne among the more common examples — draw a meaningful share of their nutrition through their root system, so a nutrient-rich substrate from the start, or root tabs pushed into the substrate near them later, matters more for these plants specifically. Water-column-feeding species, including most stem plants, floating plants, and epiphytes like Java fern and Anubias that aren't rooted in substrate at all, draw the large majority of their nutrients directly from the surrounding water, so liquid fertiliser dosed into the water column matters more for them. Most mixed-planting tanks benefit from covering both routes rather than relying on just one, since a tank stocked with both plant types will otherwise consistently underfeed one group.
All-in-One vs Estimative Index dosing
| Approach | How it works | Best suited to |
|---|---|---|
| All-in-One (AIO) | Macro and micronutrients combined in one product, dosed per the label at a fixed, generally conservative ratio | Low-to-medium light, low-tech tanks; keepers who want a simple, hard-to-get-wrong routine |
| Estimative Index (EI) | Separate macro and micronutrient solutions dosed on a set weekly schedule, with a regular partial water change to reset nutrient levels before the cycle repeats | Higher-light, CO2-injected tanks with heavier nutrient demand and a keeper willing to manage a more involved routine |
Neither approach is objectively "better" — AIO trades some flexibility for simplicity, while EI trades simplicity for more precise control over individual nutrient levels. A low-tech tank generally doesn't need EI's complexity, and a high-light, CO2-injected tank with demanding plants generally outgrows what a conservative AIO dose alone can supply.
Matching your routine to light and CO2
Fertilising doesn't operate independently of the other two inputs plants need. A heavier dosing routine matched to a high-light, CO2-injected tank is generally excessive for a low-tech setup with the same plant list, and can itself become a source of surplus nutrients algae can exploit; conversely, a conservative AIO dose that suits a low-tech tank will generally undersupply a high-light, CO2-injected setup's faster growth rate. See our lighting guide and CO2 guide for the other two legs of this balance, and revisit your fertilising routine any time you meaningfully change either.
Fish waste as a partial nitrogen source
A stocked aquarium's biological filtration converts fish waste into nitrate as the final stage of the nitrogen cycle, and plants take up a meaningful share of that nitrogen directly — part of why a well-planted, appropriately stocked tank often shows lower nitrate than an equivalent unplanted one[2]. This is a genuine, useful effect, but it's rarely a complete fertilising solution on its own: it supplies nitrogen specifically, in a ratio and quantity that depends on your stocking level, not a balanced supply of every macro and micronutrient a demanding plant list needs. Treat fish waste as one contributing input to factor into your routine, not a substitute for it.
Overfertilising and algae
Consistently dosing more nutrients than your plants, given their current light and CO2, can actually use leaves a surplus behind — and algae, which grows faster than most aquarium plants, is well placed to exploit that surplus just as it is with excess light. Overfertilising isn't the cause of every algae outbreak, and cutting dosing to zero isn't automatically the fix if plants are already nutrient-limited, but it's worth reviewing alongside light and CO2 rather than assuming more fertiliser is inherently beneficial. See our algae in aquariums guide for the wider picture on algae causes.
Common mistakes
- Assuming fish waste alone is enough to feed a planted tank, when it typically supplies nitrogen unevenly relative to everything else plants need.
- Only dosing liquid fertiliser for a tank with root-feeding species like Amazon sword or Cryptocoryne, missing the nutrition they draw through their roots.
- Using an EI dosing schedule sized for a high-light, CO2-injected tank on a low-tech setup, overshooting what the plants can use.
- Increasing fertiliser dosing to fix poor growth without checking whether light or CO2 is actually the limiting factor.
- Skipping the water change EI dosing depends on, letting nutrients accumulate beyond the schedule's intended reset point.
Frequently asked questions
Do I need to fertilise a low-tech planted tank?
Often yes, even without CO2 injection. Fish waste and decaying organic matter supply some nutrients, but rarely enough for sustained healthy growth beyond the least demanding plants, and rarely in a balanced ratio. A basic liquid fertiliser dosed a few times a week, or root tabs for root-feeding species, is a reasonable starting point for most low-tech tanks rather than assuming fish waste alone is sufficient.
What's the difference between All-in-One and Estimative Index dosing?
An All-in-One (AIO) fertiliser combines macro and micronutrients in one bottle at a fixed, generally conservative ratio, dosed according to the label — simple and hard to get badly wrong, but less adjustable if your plants need more of one nutrient than another. Estimative Index (EI) dosing uses separate macro and micronutrient solutions dosed on a set weekly schedule with a partial water change to reset nutrient levels, giving more control and generally supporting more demanding, higher-light setups, at the cost of more to learn and manage.
Do root-feeding plants need different fertilising from stem plants?
Generally yes. Root-feeding plants like Amazon sword and Cryptocoryne draw a meaningful share of their nutrients through their root system, so root tabs pushed into the substrate near them, or a nutrient-rich substrate from the start, matter more for these species specifically. Stem and floating plants draw most of their nutrients directly from the water column, so water-column dosing (liquid fertiliser) matters more for them. Most planted tanks benefit from covering both routes rather than relying on just one.
Can overfertilising cause algae?
Yes, particularly when nutrient dosing outpaces what your light and CO2 allow plants to actually use. A surplus of any input — light, CO2 or nutrients — that plants can't fully use is available for algae to exploit instead, which grows faster than most aquarium plants. Overfertilising isn't automatically the cause of every algae outbreak, but it's worth reviewing dosing alongside light and CO2 rather than assuming more fertiliser is always beneficial.
How AquaPulse can help
Nutrient dosing works on a timescale of weeks, not days — a slightly-off routine doesn't visibly harm plants immediately, it shows up gradually as slower growth, pale colour, or the kind of deficiency symptoms our nutrient deficiency guide covers. Catching that early enough to make a small correction, rather than a much bigger one later, depends on comparing this month's growth against last month's, not against a vague sense of "it seems fine."
AquaPulse works from the information and context you enter — it doesn't test your water's nutrient levels automatically. Logging dosing changes and plant condition notes in AquaPulse alongside your regular water testing keeps that comparison available over time. Get AquaPulse on the App Store or Google Play to try it, or see the Water Check feature page for more detail.
Sources and uncertainty
- Published
- 8 August 2026
- Last reviewed
- 8 August 2026
- Written and maintained by
- AquaPulse (Valeon Labs Ltd)
This guide draws on specialist aquascaping sources for the mobile-vs-immobile nutrient framework and AIO/EI dosing conventions, since no single official standard exists for ornamental planted-aquarium fertilising. The nitrogen-uptake content is consistent with, and draws on, our own already-published starting a planted aquarium guide's separately cited source on nitrogen uptake by aquatic macrophytes. We'll update this page if we find something we've got wrong.
Good to know: This guide provides general informational guidance only. It does not recommend a specific brand or product, and dosing amounts vary by product concentration — always follow your specific fertiliser's own label instructions.
- [1] Aquasabi — "Deficiency Symptoms in Aquatic Plants" Specialist aquascaping reference source. Used for the mobile (N, P, K) vs immobile (Fe, Ca, trace) nutrient framework and why deficiency location on the plant differs accordingly. Not a peer-reviewed source; presented as widely reported specialist consensus.
- [2] AquaPulse — "Starting a planted aquarium" Our own already-published, separately sourced guide (itself citing a nitrogen-uptake study). Used for plants taking up a meaningful share of tank-produced nitrogen rather than re-deriving the same research here.
What we deliberately left out: specific commercial product or brand recommendations, since suitable options and concentrations change over time and vary by region; and a universal numeric dosing schedule (exact ppm targets per week), since concentration varies by product and this guide is scoped to dosing philosophy and nutrient roles rather than a specific product's instructions — always follow your own fertiliser's label.