How Often to Fertilize Aquarium Plants: Liquids, Root Tabs

The short answer

As often as your product’s label says. Among the makers quoted here, liquid fertilizers run from daily (ADA’s Green Brighty series) to weekly (Tropica), or one to three times a week depending on product and light (Seachem Flourish, Aquarium Co-Op Easy Green). Root tabs are replaced monthly to every three to four months.

This guide covers freshwater planted tanks. Each figure is a maker’s direction for its named product or a named source’s view, shown side by side where they differ. If fish look unwell after a dosing change, test the water and contact an aquatic veterinarian.

What sets your schedule: water column, roots or soil

Liquid fertilizers feed plants through the water; tabs feed the roots. Aquarium Co-Op, an aquarium retailer that sells its own fertilizer line, says heavy root feeders “such as sword plants, cryptocoryne plants, and bulb plants — prefer feeding from the ground,” though they still take some nutrients from the water. Seachem, a US aquarium-products maker, generally suggests one or the other of its Flourish liquid and Flourish Tabs, though it says both can help in some situations.

Fish matter too. Practical Fishkeeping, a fishkeeping magazine, says “The average aquarium produces enough nitrate and phosphate, through fish waste, to keep all but the fastest growing plant species.” Tropica, a Danish aquarium-plant grower that makes its own fertilizers, splits its liquids the same way: Premium Nutrition, without nitrogen and phosphorus, is “Suitable for aquariums with few or slow-growing plants and many fish”; Specialised Nutrition, with both, is “Suitable for aquariums with many and fast-growing plants.”

The 2Hr Aquarist, which makes and sells the APT fertilizer line, says that with ADA aquasoil “The liquid dosing part is much leaner because the substrate contributes so much weight, nutrient wise.” Our guide to layering substrate in a planted tank covers soil bases and root tabs under a cap, and the Walstad method covers soil-based, low-tech tanks.

How often each maker says to dose

Liquid fertilizers, from each maker’s own directions (Tropica gives liters; the gallon figure is our conversion):

Product	Maker’s direction	Made for
Seachem Flourish	5 mL per 60 gal (250 L), once or twice a week	Micro and trace elements
Seachem Flourish Nitrogen	2.5 mL per 40 gal (160 L), twice a week or as needed	Signs of nitrogen shortage
Aquarium Co-Op Easy Green, 500 mL	1 mL per 10 gal; 1, 2 or 3 doses a week	Low, medium or high light
Tropica Premium Nutrition	6 mL per 50 L (about 13 gal), weekly	Few or slow plants, many fish
Tropica Specialised Nutrition	6 mL per 50 L (about 13 gal), weekly	Many fast-growing plants
ADA Green Brighty series	Daily application; ADA’s page gives no amount, so follow the bottle’s label	Neutral K, Brighty K (potassium), Nitrogen, Mineral (trace elements), Iron, in a planted aquarium

Aquarium Co-Op’s Easy Green light bands are 10–20 PAR (low), 20–35 (medium) and 40–50+ (high); the count “Depends on how heavily planted the tank is and how much fertilizer is being used by your plants.”

Root tabs, from each maker’s own directions:

Product	Placement	Replace
API Root Tabs	1 per 30 sq in of gravel	Monthly
Aquarium Co-Op Easy Root Tabs	1 every 4–6 in, in a grid	Monthly or as needed
Seachem Flourish Tabs	1 per 4–6 in radius	Every 3–4 months

Setting a fertilizing routine, step by step

Read the label for your product and tank volume

Each dose with an amount in the tables is set per volume of water. Seachem notes: “For smaller doses, please note that each cap thread is approximately 1 mL.” Aquarium Co-Op’s 120 mL Easy Green bottle doses “2 drops per gallon of water”, once a week for low light and twice for medium.

Match the count to your light and plants

Tropica writes of Specialised Nutrition: “We recommend 6 mL (3 pumps) per 50 L water weekly. However, we recommended that this is set in accordance with plant requirements.” For the same product it adds: “Where signs of algae growth develop, reduce the dosage by 50% and increase water changing frequency by 50%.”

Hold back or start light in a new tank, as your sources say

Tropica’s growing-in guide for new aquariums: “No fertiliser or a limited amount of fertiliser during the first 3-4 weeks. The plants contain plenty of nutrients already from the nursery, which is sufficient to establish a root network.” Root-tab makers differ: API says its tabs “help new aquatic plants get off to a vigorous start,” and Aquarium Co-Op says “When first planting, place root tabs directly under the plant.” If you are cycling the tank in the dark first, our dark start guide covers that period, which runs with no liquid fertilizer.

Dose on water-change day if your label says so

Tropica: “Specialised Nutrition is added each week when the water is changed.” For a new planted freshwater aquarium, Tropica’s guide says: “Change the water 25-50% a couple of times a week in the first 3-4 weeks. After that, change approx. 25% of the water once a week.”

Test nitrate if your fertilizer’s directions use it

For Easy Green, Aquarium Co-Op suggests “you test the water each week at first to really dial in the fertilizer dosage,” and its product page says: “We recommend having between 20–50 ppm of nitrate in your aquarium from dosing Easy Green for optimal plant growth.” Its blog guide gives 25–50 ppm for the same product. Seachem doses Flourish Nitrogen “as needed in response to signs of nitrogen deficiency (e.g. stunted growth, chlorosis),” and warns that nitrogen feeds algae “only when nitrogen levels become excessive, that is, when there is more nitrogen available than the plants can use.” Our freshwater test kit roundup covers kits that read nitrate. For readings that keep climbing, see our guide to why aquarium nitrate runs high.

Place root tabs as the label says

API: “Push midway into gravel bed.” Aquarium Co-Op: “Push the root tab at least 1 inch into the substrate for best results.” Seachem says Flourish Tabs will not alter pH, “but, in very soft or unbuffered water, they have slightly acidic properties similar to peat moss.” API’s Root Tabs safety data sheet classifies the product “Non hazardous” and says “Keep out of reach of children.” For eyes it says “Wash out immediately with water. If irritation continues, seek medical attention.” Aquarium Co-Op’s root-tab warning: “Can be irritating if it gets into your eyes, nose, or mouth. It can cause stomach upset if swallowed. If you get it on your skin, rinse off. If you get it in your eyes or mouth, rinse thoroughly for 15 minutes.” US readers can find poison-control help at poison.org, which Aquarium Co-Op names on the same page.

Watch new growth before you change the dose

Aquarium Co-Op notes that with root tabs “you have to regularly observe the heavy root feeders to see if they are melting away or showing other signs of nutrient deficiencies.” Tropica says “pale leaves often indicate lack of nutrition, but can also be due to poor growth.” Our guides to why aquarium plants die and why they turn brown cover causes other than fertilizer.

Daily, weekly or twice a week: where sources split

ADA, a Japanese aquascaping maker, describes daily application for each Green Brighty liquid, for example: “Daily application of GREEN BRIGHTY NITROGEN helps enhance leaf colors and promotes plant growth.”

The 2Hr Aquarist, which sells its own APT fertilizers, describes two ends of the range. Of the Estimative Index (EI) method it says: “EI’s approach is to overdose and then reset the levels with a large water change (50%) at the end of the week. However, over-dosing in a sparsely planted tank is an invitation to instability.” Of lean dosing: “An extensive but lean dosing regime simply means that the plants will grow more slowly – and this is the approach we would normally recommend to beginners as it is easier to control.”

Owners split as well. In a 2021 Aquarium Co-Op Forum thread, one keeper wrote that they dose once a week after the water change, while another had just switched to daily dosing. On r/PlantedTank in 2020, one owner’s whole answer was: “Every fertilizer has different dosing instructions.”

What not to do: overdosing, algae and livestock

Don’t dose more than the plants use. Seachem says nitrogen reaches algae once there is more than the plants can use (see step 5).
Cut back when algae starts, as your label says. For Specialised Nutrition, Tropica warns: “However note that if algae growth starts, Specialised Nutrition will promote this growth,” and directs a 50% dose cut with more frequent water changes (see step 2). Our guide to why aquariums grow algae covers light and other causes.
Iron can feed algae too. Explaining why its Easy Iron comes in a separate bottle, Aquarium Co-Op says that “if Easy Green contains too much iron, it could potentially lead to algae problems, such as hair algae.”
Mind copper with shrimp and snails. Asked whether Flourish’s copper is safe with shrimp, Seachem’s FAQ answers “Yes, Flourish® is safe to use with shrimp,” and adds: “It is true that in large amounts, copper can be toxic to aquatic animals and invertebrates like shrimp and snails can be particularly sensitive.” It says the copper in Flourish is (in Seachem’s wording) “so small that you would have massively overdose before you would begin to approach an amount of copper that is toxic to even the most sensitive animals.”
Expect a pH bump from some potassium liquids. ADA: “BRIGHTY K is strongly alkaline. The pH of aquarium water may rise temporarily immediately after this product is applied, but it will eventually return to the original level.”
Handle and store fertilizer safely. Aquarium Co-Op’s Easy Green page: “Store the fertilizer upright and away from children.” Its warning: “fertilizer can be irritating if it gets into your eyes, nose, or mouth, and it can cause stomach upset if swallowed. If you get Easy Green on your skin, rinse it off. If you get it in your eyes or mouth, rinse thoroughly for 15 minutes.”
If fish look unwell, test the water and contact an aquatic veterinarian.

Your product’s label is the final word.

Ready to buy?

For the nitrate step, our freshwater test kit roundup compares liquid kits and strips, and our Tank Setup & Care section gathers the site’s setup and care guides.

Frequently Asked Questions

Q. Does liquid fertilizer raise nitrate?

It depends on the product. Aquarium Co-Op says “1 mil of Easy Green in 10 gallons of water adds 3 ppm of nitrate.” Seachem says its Flourish “Does not contain significant levels of nitrogen or phosphorus.”

Q. How often should I fertilize a betta tank?

The labels quoted here that give an amount dose by water volume (Tropica and Aquarium Co-Op also by plants or light), not by fish species; step 1 gives Seachem’s and Aquarium Co-Op’s measures for small doses.

Q. Does liquid fertilizer need to be refrigerated?

For Flourish, Seachem says “Refrigeration is recommended 3 months after opening.” Aquarium Co-Op says to store Easy Green out of light for the best shelf life.

Q. Is there an aquarium fertilizer dosing calculator?

Seachem’s Flourish pages include one, and for Flourish Nitrogen Seachem also publishes a formula for a target nitrogen increase.

Sources (15)

Aquarium Tales Team

Written and reviewed by the Aquarium Tales Team. See the About page for how we work.