Fertilizer and CO2 for aquarium plants: start simple, skip the lab setup
Good news: to start out, a complete liquid fertilizer is enough — CO2 is optional. With easy plants, a nutrient-rich substrate and a weekly dose from a 10-15 € bottle, you get a lush tank with no cylinder or regulator. Injected CO2 only becomes relevant for demanding plants and brightly lit aquascapes.
What do aquarium plants actually need?
Light, carbon and nutrients, in that order. Decent LED lighting 8 hours a day, a nutrient-rich soil under the gravel and the fish’s waste already cover most of it. Liquid fertilizer tops up the potassium, iron and trace elements that are often lacking.
Which fertilizer should you start with?
- Complete liquid fertilizer (10 to 15 €, lasts 3 to 6 months): one dose a week after the water change — that’s the foundation.
- Root tabs (8 to 12 €): pushed into the substrate near hungry plants like Echinodorus or Cryptocoryne.
- Liquid carbon (10 to 15 €): a partial CO2 substitute, effective in lightly planted tanks, but dose carefully around mosses and vallisneria.
- Avoid: fertilizers rich in nitrates and phosphates in a beginner’s tank — they mostly feed algae.
When does CO2 become genuinely necessary?
When you move on to “red” plants, carpeting species (Monte Carlo, Eleocharis) or powerful lighting: without extra carbon, the equation tips out of balance and algae win, a mechanism detailed in our article on lighting duration and algae. At that point, budget 80 to 150 € for a serious CO2 kit (refillable cylinder, regulator, diffuser, bubble counter), plus 10 to 20 € per refill. The disposable 30 € mini-kits quickly end up costing more.
Which plants thrive without CO2?
Anubias, Java moss, Java fern, Cryptocoryne, Vallisneria, Hygrophila, Ceratophyllum: these classics grow on a simple liquid fertilizer and forgive missed doses. A tank densely planted with easy species is also the best algae and nitrate control there is. More layout ideas in the decor and plants category.
Frequently asked questions
Is fertilizer dangerous for shrimp?
Modern aquarium-formulated fertilizers are safe at the stated doses. Do watch out for overdosed liquid carbon and copper-rich fertilizers, though.
Should CO2 be switched off at night?
Yes, with a solenoid valve (30 to 40 €) or manually: at night, plants don’t use CO2 and it would drag the pH down for nothing.
My plants are yellowing despite fertilizer — why?
Most often an iron or potassium deficiency, or ageing lighting. Try a dedicated iron fertilizer before investing in CO2.
This guide is part of Planète Pets’s Fishkeeping universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.