A planted aquarium starts with substrate, lighting, and water chemistry—not fish
A planted aquarium is a tank where live plants are the foundation, not an afterthought. The plants consume nitrates that would otherwise poison fish, produce oxygen, and give bacteria a place to colonize. This means you set up the tank, plant it, let it run for two to four weeks, and only then add fish. Rushing this step is the most common reason planted tanks fail.
The basic order is: tank and stand, substrate (the material on the bottom), hardscape (rocks and wood), water, filter, heater, lighting, plants, then fish. Each step affects the ones that follow, so skipping ahead or reversing the order usually means tearing down and starting over.
Key Takeaways
- Substrate depth matters: aquatic soil needs 2 to 3 inches, and sand or gravel needs 1 to 2 inches, because plant roots need to anchor and access nutrients.
- Lighting runs 8 to 10 hours per day and must be strong enough for the plants you choose—low-light plants need 8 to 12 micromoles per second per square meter, high-light plants need 25 or more.
- The nitrogen cycle takes two to four weeks: beneficial bacteria colonize the filter and substrate, converting fish waste into forms plants can use, and the tank is not ready for fish until ammonia and nitrite both read zero.
- Water parameters vary by plant type, but most planted tanks run pH 6.0 to 7.0, general hardness between 4 and 8 dGH, and carbonate hardness between 3 and 6 dKH.
- Plants need macronutrients (nitrogen, phosphorus, potassium) and micronutrients (iron, boron, manganese), which come from fish waste, substrate, or liquid fertilizers depending on your stocking level.
Choosing tank size and location
Larger tanks are more forgiving than small ones. A 20-gallon long tank (30 inches × 12 inches × 12 inches) is a practical minimum for a beginner because the water volume buffers against temperature swings and chemistry shifts. Tanks smaller than 10 gallons swing wildly and are harder to keep stable.
The stand must be level and able to hold the full weight—a 20-gallon tank with water, substrate, and hardscape weighs roughly 200 pounds. Place the tank away from direct sunlight, which causes algae blooms, and away from heating vents or air conditioning, which cause temperature fluctuations. A spot against an interior wall, near an electrical outlet, is ideal.
Substrate selection and layering
Aquatic soil (brands like ADA Aquasoil or Flourite) is the best choice for rooted plants because it is porous, holds nutrients, and lowers pH slightly. Lay it 2 to 3 inches deep. Sand and gravel work too but hold fewer nutrients, so you will need to dose fertilizers more often. If you use sand or gravel, 1 to 2 inches is enough.
Many planted tanks use a two-layer system: a nutrient-rich layer on the bottom (aquatic soil or laterite clay), then a cap of inert sand or gravel on top to prevent the nutrient layer from clouding the water. This is optional but reduces maintenance. Rinse the top layer before adding it so the water stays clear when you fill the tank.
Hardscape, water, and the filter setup
Hardscape—rocks, driftwood, or both—gives the tank structure and provides surface area for beneficial bacteria. Arrange it before adding water so you do not have to move it later and disturb the substrate. Soak driftwood in a bucket for 24 to 48 hours before adding it; this prevents it from floating and leaches out tannins that darken the water (which is harmless but looks brown).
Fill the tank slowly, pouring water onto a plate or into a cup so the substrate does not cloud. Use tap water unless your tap water is very hard or very soft; in that case, research your local water parameters first. Once the tank is full, install the filter. A hang-on-back filter or canister filter rated for the tank size works well. Run it for a few hours to make sure it is working, then leave it running continuously.
Add a heater set to 72 to 78 degrees Fahrenheit (22 to 26 Celsius), depending on the plants and fish you plan to keep. Most tropical plants and fish prefer the warmer end of that range. Let the tank sit for 24 hours so the water temperature stabilizes and any cloudiness from filling settles.
Lighting and the nitrogen cycle
Install lighting above the tank. LED lights are efficient and run cool; aim for 8 to 12 watts per gallon for low-light plants, or 15 to 25 watts per gallon for high-light plants. Set a timer to run the lights 8 to 10 hours per day. Too much light causes algae; too little causes plants to grow slowly or die.
Now the tank sits and runs without fish for two to four weeks. During this time, the nitrogen cycle begins: bacteria colonize the filter media and substrate, and they start converting ammonia (from decaying plant matter and the initial bacterial bloom) into nitrite, then into nitrate. Test the water every few days with a liquid test kit. When ammonia and nitrite both read zero and nitrate is present, the cycle is complete and the tank is ready for fish.
Do not skip this step or rush it. A tank without a cycled filter will poison fish with ammonia and nitrite. If you add fish before the cycle is done, you will need to do large water changes every day or two to keep ammonia and nitrite low enough that fish survive.
Planting and fertilizer dosing
Plant rooted plants (stem plants, sword plants, crypts) into the substrate so the roots are buried and the crown (where the stem meets the roots) is at the surface. Foreground plants go in the front, midground in the middle, and background plants in the back. Leave space between plants—they will grow and fill in over weeks.
Floating plants (water sprite, frogbit, salvinia) straightforward float on the surface. Tie or weigh down plants that want to float but you want to stay planted (like moss or anubias) to rocks or driftwood with fishing line; do not bury them, or they will rot.
After planting, dose fertilizer based on your stocking level. A heavily stocked tank (many fish) gets enough nitrogen and phosphorus from fish waste, so you only need to add micronutrients (iron, boron, manganese) once or twice a week. A lightly stocked tank needs all macronutrients and micronutrients. Liquid all-in-one fertilizers (like Thrive or Flourish) are easier than dosing individual nutrients. Follow the bottle instructions and adjust based on how fast plants grow.
Adding fish and ongoing maintenance
Once the cycle is complete and plants are established (usually two to four weeks after planting), add fish slowly. Start with a small number—half the bioload you plan for—and wait a week before adding more. This lets the bacteria population grow to match the new waste load.
Weekly maintenance includes a 25 to 50 percent water change, checking that the filter is flowing normally, and dosing fertilizer. Monthly maintenance includes cleaning the filter intake (not the media itself, which holds bacteria) and checking that the heater and lights are working. Do not clean the filter media in tap water; rinse it in old tank water so you do not kill the bacteria.
Algae will appear at some point. A little algae is normal and harmless. If it takes over, reduce lighting hours, do more frequent water changes, or add algae-eating fish like Otocinclus or Amano shrimp. Do not use algae-killing chemicals in a planted tank; they kill plants too.
Water parameters and testing
Test your water once a week for the first month, then once every two weeks after that. You need to know ammonia, nitrite, nitrate, pH, and general hardness. A liquid test kit (API Master Test Kit) is more accurate than strips and costs less over time.
The table below shows what each parameter means and why it matters. Ammonia and nitrite must stay at zero; nitrate should stay between 5 and 20 ppm to feed plants without feeding algae. pH and hardness vary by the plants you choose, but most planted tanks run slightly acidic and moderately soft.
| Parameter | Target Range | Why It Matters |
|---|---|---|
| Ammonia | 0 ppm | Toxic to fish; indicates the cycle is not complete or the filter is failing |
| Nitrite | 0 ppm | Toxic to fish; the second stage of the nitrogen cycle |
| Nitrate | 5–20 ppm | Plant food; above 40 ppm causes algae blooms |
| pH | 6.0–7.0 | Most plants and fish prefer slightly acidic water |
| General Hardness (GH) | 4–8 dGH | Affects nutrient availability; too soft or too hard stresses plants |
Frequently Asked Questions
Can I add fish before the nitrogen cycle is complete?
No. Ammonia and nitrite are toxic even at low levels, and fish will become stressed or die. If you add fish before the cycle finishes, you must do 50 percent water changes every day or two to keep ammonia and nitrite below 1 ppm. It is much easier to wait two to four weeks and cycle the tank first.
Why are my plants turning yellow or growing slowly?
Yellow leaves usually mean iron deficiency or nitrogen deficiency. Iron deficiency shows as yellow leaves with green veins; nitrogen deficiency yellows the whole leaf. Dose an all-in-one fertilizer or add iron separately. Slow growth means too little light, too little fertilizer, or too much algae competing for nutrients. Increase lighting hours to 10 per day and dose fertilizer more often.
What plants are easiest for beginners?
Anubias, Java fern, and Cryptocoryne are nearly impossible to kill and grow in low light. Stem plants like ludwigia and rotala grow fast and are forgiving. Avoid plants labeled "difficult" or "high-light" until you have experience. Ask your local aquarium store which plants do well in your tap water.
Do I need CO2 injection?
No. Most beginner planted tanks work without CO2. Plants grow slower without it, but they still grow. Add CO2 only if you want fast growth or plan to keep high-light, high-demand plants. A basic system costs $100 to $300 and requires a regulator, diffuser, and refillable cylinder.
How often should I do water changes?
A 25 to 50 percent water change once a week is standard. If nitrate climbs above 40 ppm between changes, increase the change size or frequency. If you have very few fish and many plants, you may only need a 25 percent change every two weeks. Test nitrate to know for sure.