Does a planted tank always need CO2?

No, it depends on the species. Low demand plants such as mosses, Java fern, Anubias and Cryptocoryne grow perfectly well without CO2, while high demand plants such as dwarf hairgrass, Monte Carlo and Ludwigia will stretch, drop leaves and throw aerial roots without it. The CO2 field in the atlas is the rule: required means it has to be injected, optional means the plant lives either way.

Which plants work in a low light tank?

Filter the light field for low and medium, and favour mosses, ferns, Anubias and rosette plants: Java moss, Java fern, Anubias nana, Cryptocoryne, Vallisneria and hornwort all cope. Avoid carpeting species such as dwarf baby tears and dwarf hairgrass, and avoid the red varieties, because a low light tank cannot supply what they need and they turn pale and leggy instead of red.

What hardness suits a planted tank?

Most common aquatic plants grow normally between 4 and 10 dGH. The soft water group covers the Tonina and Eriocaulon types, many red plants and most aquarium mosses; the hard water group includes Vallisneria, hornwort and some of the Sagittaria species. Hardness also governs the relationship between CO2 and pH: at the same CO2 concentration a lower KH lets pH fall further, which is why low KH tanks need a reduced CO2 injection rate.

Why have my plants stopped growing while algae takes over?

In most cases light and CO2 are out of balance. Light is plentiful but CO2 is short, so the plants cannot obtain carbon and stall, while algae keep growing at low CO2 and win the competition. Fix it in this order: confirm the CO2 level first, measured by pH and KH rather than by counting bubbles in the counter, then set the photoperiod from six hours and add thirty minutes a week, and only then look at fertiliser dosing.

What is the difference between low demand and high demand plants?

It is defined by light and CO2 demand, not by price or rarity. Low demand plants such as mosses, ferns and Anubias survive on low light with no CO2, grow slowly and rarely need trimming. High demand plants such as carpeting species, red varieties and stem plants need medium to high light plus CO2, grow quickly and need regular trimming. Mix both in one tank and the light and CO2 get set for the high demand group, which leaves the low demand plants prone to algae, so most keepers either run separate tanks or build around one group.

G-02 · Freshwater / Marine

Plant atlas

The usual reason plants fail is not a lack of skill but a mismatch between the light tier and the CO2 tier: a high light plant in a low light tank stretches and drops leaves, and a low light plant under strong light burns and grows algae instead. The atlas therefore puts light and CO2 first and quotes a PAR figure, because wattage cannot be compared between fixtures while PAR can. The hardness field decides whether you can keep the soft water species at all, such as the Tonina and Eriocaulon types, and whether the trace elements in your fertiliser stay dissolved or precipitate out.

Light and CO2 decide whether a plant survives, hardness, substrate and fertiliser decide how well it grows, and that order cannot be reversed.

Units: temperature in °C, hardness in German degrees (dGH / dKH), marine salinity as specific gravity at 25 °C, volume in litres. These are the values recorded for the species and do not follow the site unit switcher.

Light

CO₂

Growth rate

Level

22 of 22 entries

Plant atlas
Name	Light	PAR	CO₂	Hardness	Growth	Placement	Level
Java FernMicrosorum pteropus爪哇蕨	Low light	15–30	Optional	2–12 dGH	Slow	Midground / Attached	Beginner
Java MossTaxiphyllum barbieri爪哇莫斯	Low light	15–30	Optional	2–15 dGH	Medium	Foreground / Attached	Beginner
Christmas MossVesicularia montagnei圣诞莫斯	Medium light	30–50	Optional	1–10 dGH	Slow	Foreground / Attached	Moderate
Dwarf AnubiasAnubias barteri var. nana小水榕	Low light	15–30	Not needed	2–15 dGH	Slow	Foreground / Midground / Attached	Beginner
Anubias Nana PetiteAnubias barteri var. nana 'Petite'迷你水榕	Low light	15–30	Not needed	2–15 dGH	Slow	Foreground / Attached	Beginner
Amazon SwordEchinodorus amazonicus亚马逊剑	Medium light	35–60	Optional	3–12 dGH	Medium	Background / Specimen	Beginner
Wendt CryptocoryneCryptocoryne wendtii温蒂椒草	Medium light	30–50	Optional	2–12 dGH	Slow	Foreground / Midground	Beginner
Balansae CryptocoryneCryptocoryne crispatula var. balansae巴拉椒草	Medium light	30–60	Optional	3–15 dGH	Slow	Midground / Background	Moderate
Red Tiger LotusNymphaea zenkeri红虎耳	Medium light	40–60	Optional	3–12 dGH	Medium	Midground / Specimen	Beginner
Banana PlantNymphoides aquatica香蕉草	Medium light	30–60	Optional	2–10 dGH	Slow	Foreground / Midground / Specimen	Beginner
Water WisteriaHygrophila difformis水芹	Medium light	30–60	Optional	2–12 dGH	Fast	Midground / Background	Beginner
Roundleaf RotalaRotala rotundifolia大血心兰	High light	60–100	Recommended	2–12 dGH	Fast	Midground / Background	Beginner
Red LudwigiaLudwigia repens红蝴蝶	High light	60–90	Recommended	2–12 dGH	Fast	Midground / Background	Beginner
Carolina FanwortCabomba caroliniana水盾草	Medium light	40–60	Recommended	2–10 dGH	Fast	Background	Moderate
Parrot FeatherMyriophyllum aquaticum大聚藻	Medium light	40–60	Optional	2–12 dGH	Fast	Midground / Background	Beginner
Dwarf HairgrassEleocharis acicularis牛毛毡	High light	60–100	Recommended	2–12 dGH	Medium	Foreground / Carpet	Moderate
Monte CarloMicranthemum tweediei 'Monte Carlo'迷你矮珍珠	High light	60–100	Recommended	2–12 dGH	Medium	Foreground / Carpet	Moderate
GlossostigmaGlossostigma elatinoides矮珍珠	Very high light	110–160	Required	2–10 dGH	Medium	Foreground / Carpet	Advanced
Creeping StaurogyneStaurogyne repens爬地矮珍珠	Medium light	40–60	Optional	2–12 dGH	Slow	Foreground / Midground	Beginner
VallisneriaVallisneria natans苦草	Medium light	30–60	Optional	4–15 dGH	Fast	Background	Beginner
Common DuckweedLemna minor浮萍	Medium light	30–60	Not needed	2–15 dGH	Fast	Floating	Beginner
Floating FernSalvinia natans槐叶萍	Medium light	30–60	Not needed	2–12 dGH	Fast	Floating	Beginner

How to use it

Step 1Set the light tier, then choose plantsWork from the fixture you already own. A low light tank should take low and medium light plants only; a high light plant in it will stretch or burn rather than thrive.
Step 2Treat CO2 as a requirement, not a bonusA plant marked as requiring CO2 will not grow without it. A plant marked as optional does better with it and still lives without it.
Step 3Rule out soft water species on hardnessA plant that needs soft water will stall at the growing tip with blackened roots in hard water, and no amount of fertiliser brings it back.
Step 4Plan trimming around growth rateFast growers need a trim every two to three weeks. Plant a whole tank of them without the time to keep up and the canopy shades out everything beneath within a month.

Frequently asked questions

Does a planted tank always need CO2?: No, it depends on the species. Low demand plants such as mosses, Java fern, Anubias and Cryptocoryne grow perfectly well without CO2, while high demand plants such as dwarf hairgrass, Monte Carlo and Ludwigia will stretch, drop leaves and throw aerial roots without it. The CO2 field in the atlas is the rule: required means it has to be injected, optional means the plant lives either way.
Which plants work in a low light tank?: Filter the light field for low and medium, and favour mosses, ferns, Anubias and rosette plants: Java moss, Java fern, Anubias nana, Cryptocoryne, Vallisneria and hornwort all cope. Avoid carpeting species such as dwarf baby tears and dwarf hairgrass, and avoid the red varieties, because a low light tank cannot supply what they need and they turn pale and leggy instead of red.
What hardness suits a planted tank?: Most common aquatic plants grow normally between 4 and 10 dGH. The soft water group covers the Tonina and Eriocaulon types, many red plants and most aquarium mosses; the hard water group includes Vallisneria, hornwort and some of the Sagittaria species. Hardness also governs the relationship between CO2 and pH: at the same CO2 concentration a lower KH lets pH fall further, which is why low KH tanks need a reduced CO2 injection rate.
Why have my plants stopped growing while algae takes over?: In most cases light and CO2 are out of balance. Light is plentiful but CO2 is short, so the plants cannot obtain carbon and stall, while algae keep growing at low CO2 and win the competition. Fix it in this order: confirm the CO2 level first, measured by pH and KH rather than by counting bubbles in the counter, then set the photoperiod from six hours and add thirty minutes a week, and only then look at fertiliser dosing.
What is the difference between low demand and high demand plants?: It is defined by light and CO2 demand, not by price or rarity. Low demand plants such as mosses, ferns and Anubias survive on low light with no CO2, grow slowly and rarely need trimming. High demand plants such as carpeting species, red varieties and stem plants need medium to high light plus CO2, grow quickly and need regular trimming. Mix both in one tank and the light and CO2 get set for the high demand group, which leaves the low demand plants prone to algae, so most keepers either run separate tanks or build around one group.