Setting up a planted aquarium can be extremely confusing, especially for beginners.
Anyone can throw together a simple 10 gallon tank with gravel and cheap decorations; unfortunately, the same cannot be said for planted tanks.
Planted tanks have a unique set of requirements, some of which can be tricky to get just right.
That said, planted aquariums are extremely beautiful when done correctly. There is something simply amazing about an aquarium filled with luscious green plants. It’s almost like a piece of the Amazon River right in your living room.
In this guide, we will take you through the step-by-step process of setting up a planted tank. We will cover all of the necessary steps and equipment, so bookmark this for future use if you don’t plan on reading it all right now!
A Few Things You May Need
You may have to pick up a few pieces of equipment before setting up a planted aquarium. Here are a few things you may need:
- LED Lighting: I always recommend the Finnex Planted+ or the Finnex FugeRay. Finnex is a great brand and I cant recommend them enough. Also, their LED lights are made specifically for planted tanks.
- Substrate: Choosing a substrate is something that a lot of people struggle with. I would recommend either ADA AquaSoil (if you’re looking for something with lots of nutrients) or Eco Complete (no nutrients, but very high quality).
- Heater: A heater is an absolute necessity for any tank. I recommend the Cobalt NeoTherm.
- Filtration System: The type of filter you need really depends on your setup. If you’re setting up a tank larger than 40 gallons or so, you probably want to go with a canister filter. For smaller setups, a hang on back unit is usually fine. Check out this guide that covers the best fish tank filters on the market.
- Test kit: This is an absolute must when setting up a planted aquarium. The API Freshwater Master Test Kit is the most accurate on the market.
- Carbon Dioxide Supplements: as you probably know, CO2 is critical to plant health. As one of the main components for photosynthesis, healthy plant growth can be accelerated through supplements like API’s CO2 Booster, homemade, and prefab reactors like Sera Flore Active’s CO2 Reactor.
Step 1: Choosing a Substrate
Choosing a substrate for a non-planted tank is really easy – Just pick any type of gravel and you’re good to go.
So why doesn’t this work for planted tanks?
The answer is simple; plants need nutrients to survive.
Gravel, though simple and easy to clean, is sterile when first added to a tank. And because the grains are so large, it does not hold nutrients well enough to support most aquatic plants.
Think about the last time you ran your hands through the muck at a beach or river. The grains are all different sizes, from sand to rocks.
The varying sized grains allow organic material to collect and create better anchors for healthier root systems.
Inert vs. Active Substrates
When choosing a substrate for your planted aquarium, you basically have two choices – an inert substrate or an active substrate. In this section we will describe the differences and the pros vs. cons for each type.
Inert substrates do not contain any plant-specific nutrients. If you decide to use an inert substrate, you have to add fertilizers (either root tabs or water soluble fertilizers) to the tank to help feed you plants.
That being said, inert substrate basically last forever and do not break down. In addition, they are generally easier to manage that active substrates and do not encourage algae growth
- Pros – last forever/do not break down, easy to manage, usually pretty cheap
- Cons – do not contain any of the nutrients plants need to survive, so additional fertilizers are necessary
Active substrates are packed full of plant specific nutrients. If you’re looking for aggressive plants growth, an active substrate is the way to go.
On the down side, active substrates can be a little harder to manage – they tend to stir up easily (making it hard to move around your plants) and can be a bit expensive.
- Pros – packed full of nutrients, encourage plant growth
- Cons – expensive, can cause ammonia spikes, need to be replaced every few years
Types of Planted Aquarium Substrate
So we know that plain gravel probably isn’t the best choice. Luckily, there are a few types of substrate that help nutrients well and facilitate great plant growth!
We mentioned a bit about our favorite choices earlier in the article, but now we will go into a little more depth:
Flourite is made from several different materials, including volcanic soil and clay. But what they all have in common is a non-compacting way of settling and a porous structure that allows both free water flow and nutrient collection.
This way, supplements, micro-organisms, plant roots, and organic matter can collect and create a living network throughout the substrate!
Quite a different picture from the hard lumps of gravel work, isn’t it?
If you decide to use Flourite, it is probably best to add a few root tabs (small discs that contain tons of nutrients and “leach” it into the substrate).
Flourite holds onto nutrients and then re-releases them over time in a natural, controlled fashion. This way, more of your supplements are taken up by plants as actual food, rather than being wasted in the water column, filtered out, or broken down by bacteria, in the case of traditional gravel substrates.
I recommend Fluval Plant and Shrimp Stratum for an amazingly sleek look on top of the incredible nutrient sponge capacity.
All-in-One Substrates (Active)
These substrates use actually a “mix” of several different types of substrate and are pre-packed with tons of nutrients (so there is no need for root tabs!).
If you’re looking for some serious plant growth, all-in-one substrates can’t really be beat. ADA Aqua Soil is a leader in the industry for all-in-one substrates and we highly recommend them if you want to go this route.
Note: If you decide to use a substate that is pre-packed with nutrients, make sure that you don’t have any fish present in the tank when you add it.
The spike of nutrients can cause high levels of ammonia for the first few days, which can be deadly for fish.
Check out our detailed article on the types of planted aquarium substrate if you would like more info on the topic.
Note: If you decide to use a substrate that is pre-packed with nutrients, make sure that you don’t have any fish present in the tank when you add it. The spike of nutrients can cause high levels of ammonia for the first few days as bacteria start to consume the new materials, which can be deadly for fish. Pre-loaded substrates can also shift the water’s pH and other chemical parameters too quickly for fish, causing death. Normally, acclimating fish to new pH levels is a process that takes days to weeks. Check out our detailed article on the types of planted aquarium substrate if you would like more info on the topic.
Laying the Substrate
Plant substrates have a pesky habit of clouding up the entire tank if not laid down correctly. Honestly, this can be one of the most frustrating parts of setting up a planted aquarium.
Before you attempt to put ANYTHING into the aquarium, make sure to rinse the substrate.
Floating dust is irritating to animal gills and just looks bad, plain and simple.
Use a five gallon bucket and rinse it until the water runs relatively clear. Nowadays, a lot of substrates claim that a pre-rinse is unnecessary but I usually do it anyways.
Next, lay 2 to 3 inches of substrate in your tank. A lot of people like to top it off with some gravel to hold everything together better, but this is completely optional (sand it also a good option, but make sure to only use aquarium sand).
It is important to know that even the best-washed substrate in the world will cause a mess if you don’t fill the tank carefully, so add water slowly!
A great tip to avoid a ton of clouding is to place a plate (any old dinner plate should do) on top of your newly-laid substrate and dump the non-chlorinated water onto the plate instead of directly onto the substrate.
This will prevent it from stirring up the soil/gravel and save you a huge headache. Do not rush this step!
Step 2: Lighting
Getting your hands on a good light fixture is vital when setting up a planted aquarium.
While most full aquarium hoods include fluorescent fixtures, the basic fluorescent bulbs they come with simply won’t cut it because the spectrum is wrong.
The light spectrum of a bulb is the wavelengths of light they create. Plants need specific wavelengths for optimal growth and even if you have a ton of light, it’s not always the right kind.
Normally, these bulbs create a color cast optimized for nice appearance. But these bulbs are usually too warm in temperature (under 5000K), too cool (above 7000K), and always far too dim!
And the deeper and larger your tank is, the more lights you need to keep your plants looking lush. As a very rough rule of thumb, we can use the following formula:
- 0.25 Watts per Liter of water: Low Light Level
- 0.50 Watts per Liter: Moderate Light Level
- 0.80 to 1.0+ Watts per Liter: High Light Levels
A light fixture is definitely something you don’t want to skimp on; buying knock-off light fixtures will probably cost you more in the long run and can even be a fire hazard. Luckily, good lighting can actually be pretty cheap.
Suggested Planted Aquarium Lights
Here are some of our most recommended light fixtures for planted tanks:
- Beamswork EA Timer – Definitely the most affordable light fixture on our list. Despite the low price tag, this unit packs quite a punch. In addition, it does a great job at hindering algae growth, which is pretty amazing for a light of this price range.
- Finnex FugeRay – The FugeRay is mid way in the pack in terms of price. The low profile fixture offers great power while boasting an ultra slim frame, so it definitely won’t take away from the look of your tank. Finnex makes amazing lights, so you really can’t go wrong with the FugeRay.
- Finnex Planted+ 24/7 – The Planted+ is a little on the pricier side, but you are definitely paying for quality. This unit has tons on extra features, such as sunrise and starry night simulators, customizable color channels, and storm effects. Though not necessary for plant health, these effects can really help bring your tank to life. In addition, the Planted+ is known for bringing out vivid colors, especially in red plants.
LEDs, fluorescent strips, and compact fluorescent fixtures are the most common lighting choices for your planted aquarium setup.
All work equally well, with LEDs being the most expensive but most efficient and longest lasting.
Compact fluorescents are a great happy medium. And fluorescent lights are the cheapest and shortest lasting, but still more efficient and longer lived than incandescent bulbs, sometimes provided in the very cheapest aquarium setups.
Incandescent fixtures are the worst choice for any aquarium, planted or otherwise.
As anyone who has ever touched a light bulb knows, they kick out a ton of heat, which can actually alter the water temperature in a small aquarium. Also, any splash of water can cause them to shatter, creating not only a glass hazard but an electrical shock hazard as well.
Feeling out a Light Cycle
When setting up a planted aquarium, it is important to know that no two tanks are alike. There is no magic light cycle or a certain number of hours you have to keep your lights on.
That said, I start out keeping my lights on somewhere between 10-12 hours a day If I want a little more growth out of my plants, I bump up the light cycle by an hour or two.
If I notice algae growth, I scale back a little. Some plants will be happy with 10 hour days while others may like a little more. It is important to feel out your tank and try out different cycles to get good growth and avoid algae.
What’s important is that you have one, however. Aquatic plants monitor light to figure out seasons, when to increase growth, when to slow it down, etc, just like surface plants do!
Step 3: Filtration
Pick out your filtration system may not be the most “fun” part of setting up a planted aquarium, but it’s important nonetheless. That said, I believe that most people tend to overthink their filtration setups. My recommendations are rather simple:
Tanks Under 50 Gallons
Smaller planted aquariums under 50 gallons (especially beginner tanks) are completely fine with hang on back filtration units.
Though not as powerful as their canister counterparts, HOB units are convenient, easy to clean, and function well.
I recommend the AquaClear Power Filter.
Tanks 50+ Gallons
Larger tanks over 50 gallons are best suited for canister filters.
Canister filters are capable of processing much more water, which can be a necessity for hard-to-keep plants like Madagascar Lace Plants.
Canister filters also have chambers you can customize with mediums specific to your needs.
Want to lower the pH for your Amazonian setup? Add some peat moss!
Having issues with ammonia buildup? Zeolite packages occupying one section are a great solution.
I recommend the EHEIM Classic. Combining a canister filter with a powerhead also allows you to potentially create a flowing water ecosystem. Instead of a “pond” aquarium, you can instead make a stream or river!
Important note: Whichever type of filtration system you choose, make sure to remove any activated carbon. While useful in a fish-only system, activated carbon removes the nutrients that your plants need to thrive.
I don’t recommend under gravel filters anywhere, especially in the planted aquarium. All they do is collect material under the gravel for it to rot over time. And cleaning out one involves ripping up your substrate, making a tremendous mess, spiking toxic chemical levels, and adding organics to the water column. Avoid at all costs!
Step 4: Adding Plants to Your Setup
One of the frustrating parts of setting up an aquarium is staring at an empty tank for weeks while it cycles.
In case you’re unaware, “cycling” a tank is the process where beneficial bacteria and other organisms develop and grow.
These bacteria help break down ammonia and other toxic compounds your fish and plants release into less toxic or even beneficial compounds critical for growth.
If you add all your fish at once into a non-cycled tank, the waste they release can pile up, causing stress and eventual death.
Plants are another story. Now you’re probably wondering – “Is it necessary to cycle my aquarium before adding live plants?”
Luckily, the answer is no!
In fact, live plants can actually help speed up the entire cycling process.
Make sure you still monitor the cycling process closely and never add fish until ammonia and nitrites are completely undetectable. In a fresh tank, this shouldn’t be a concern to begin with, but it never hurts to be safe.
You always want to add just a few fish to begin, to help start the cycling process.
Weekly, if your water parameters look good, you can add a few more, until you reach the carrying capacity of your aquarium.
Suggested Beginner Plants & Placement
As a beginner, it is important to start out with some easy-to-keep plants. These plants won’t require any special dosing or upkeep other than some occasional trimming:
- Java Moss (Carpet to Rock Accent Plant!) This low light plant grows extremely quickly, acting as a great nutrient sponge in case of overfeeding or chemical imbalance. Small fish and invertebrates also love wandering through the thickets it creates. Java Moss can attach to nearly any surface as well, including plastic filter piping if you need to hide them from view!
- Anubias Nana (Foreground to Rock Accent) Anubias are a strange genus of plant from Africa. They’re slow growing but extremely hardy. If your Anubias is dying, you’re doing something majorly wrong! They’re also tolerant of low light and actually prefer being attached to rocks or driftwood. In the wild, they grow in the splash zone of streams with alternating periods of submersion.
- Crypt Wendtii (Foreground) This Sri Lankan Cryptocoryne is a smaller species with beautiful reddish brown leaves. Like most crypts it’s quite hardy and does well in a beginner’s planted aquarium!
- Pygmy Chain Sword (Foreground) These are a great foreground plant if you’re looking to create a mini-jungle for small fish and shrimps!
- Micro Sword (Foreground) If you want your tank to feel like a lawn, Micro Sword plants are one of the best choices! Keep in mind they have medium to high light requirements, prefer a rich substrate, and have a relatively slow growth rate.
- Cryptocoryne (Mid-Ground) Coming in a variety of species, Cryptocoryne are not only very inexpensive and hardy but extremely attractive. They often come in dried bulb form as well, allowing you to establish your plants from the very beginning. Cryptocoryne are great show plants for tanks with medium to low light levels!
- Java Fern (Mid-Ground to Rock Accent) Like Anubias, Java Ferns are a hardy, low light tolerant species that are a great choice for a planted aquarium. WIth broad dark leaves, these ferns can grow in a substrate but prefer to be attached to rocks or driftwood! They even have a unique breeding method where young plants bud from the adult leaves!
- Water Wisteria (Background) These plants are one of the most common plants for the new planted aquarium! While tolerant of low light, they prefer having as much as possible and will reward you with tiny, streaming bubbles of O2 as they busily photosynthesize! They must have a rich substrate, however, or they’ll quickly die out!
- Amazon Sword (Background) One of the showiest of common aquarium plants for the planted tank, the various species of Amazon Sword Plant can grow feet in height and diameter. They love as much light and nutrients as you can offer and those broad leaves can be algae prone. This makes them natural platters for algae eating fish and shrimp!
- Hornwort (Background/Floating) Hornwort is so easy to grow that you don’t even have to stick it into the substrate. It actually prefers to simply float where it’s closest to rich light and can passively soak up nutrients from the water. Keep in mind that while attractive, floating plants will block light to the lower levels of the water column. Hornwort can also quickly grow out of control when floating and needs to be weeded constantly.
These plants do exactly as their name suggests; carpet you tank floor is a beautiful green carpet. Carpeting plants such as Java Moss tend to grow quickly and easily, attaching to substrate, rocks, and driftwood at it grows. Keep in mind they often need open access to light; large plants like Amazon Swords and floating plants like Duckweed and Hornwort can shade them, causing them to weaken and die.
Foreground plants are meant to be placed in the very front of the tank. They tend to stay relatively short, so your view of the back of the tank won’t be obstructed. Species such as Anubian Nana and Pygmy Chain Swords offer great fill, but don’t take away from the look of your “main” pieces.
Mid-Ground plants should be planted near the middle of the tank and are slightly taller than foreground plants. They tend to be a little thicker and fill out more of the tank, so they give the aquarium a nice “full” feeling. Mid-ground plants create a transition zone to the background.
These are your main piece showstoppers. Plants such as Amazon Swords are large, thick, and tend to be the main attraction. They are usually placed at the very back of the tank as to not obstruct the view. You’ll also usually have fewer background plants due to their space requirements. They also have a tendency to create large amounts of shade, so space them accordingly.
Proper Plant Care
There is more to setting up a planted aquarium than throwing some plants in a tank and calling it a day. Planted aquarium require a certain level of care to stay healthy.
Here are a few tips to keep your plants happy and healthy:
- Bi-weekly water changes are a must – Water changes are beneficial for several reasons. Nitrate (hopefully no ammonia or nitrite) tend to build up in your tank over time. Unfortunately, sufficient filtration can only get nitrate levels down so far. Bi-weekly water changes help bring down nitrates to safe levels. When doing a water change, you should also consider adding a boost of beneficial trace elements like iron and potassium to aid plant growth and health!
- Keep temperatures stable – There are tons of opinions and studies about the perfect temperature for planted tanks (I recommend somewhere between 78-82 degrees but this really depends on the plants, fish, and ecosystem you’re developing). In reality, keeping your water temperature stable is far more important than the actual temperature because both fish and plants can adapt to a few degrees in either direction. A reliable, good quality heater is a must. I use the Cobalt Aquatics Neo-Therm and it has served me well for years.
- Trim your plants occasionally – Don’t get me wrong. Letting you plants grow out and fill up the tank is amazing to watch and you should definitely let this happen. You should try to avoid excessive growth, especially when it comes to tall plants. Tall plants that grow large can create too much shade, killing plants below them by restricting access to light. Trim your plants once in a while to make sure they’re not blocking other plants below. Dead and dying leaves should also be removed as needed. Pruning encourages new growth in aquatic plants as much as in your garden. And it keeps rotting matter from creating problems for your water chemistry.
Fertilizing your Plants
Low-tech setups usually don’t require and sort of dosing or special additions in terms of trace elements. A few fish should do this trick to keep you plants happy.
But, just like gardens, setting up a planted aquarium sometimes requires fertilization. The plants will often let you know with slowed growth, discoloured leaves, and other signs of weakness.
Here are two types of fertilizers that can help you achieve explosive growth in your new planted aquarium!
- Substrate Fertilizers – Substrate fertilizers are placed underneath of the substrate. These are especially effective when used with substrates such as Flourite due to its high CEC (ability to absorb nutrients). Plants use the nutrients over time, so nothing goes to waste.
- Liquid Fertilizers – Liquid fertilizers are most effective for plants that don’t grow roots in the substrate, such as Java Moss. Since they are unable to absorb nutrients from within the substrate, they pull nutrients from the water. Be careful with liquid fertilizers; they tend to promote algae growth if dosed in high quantities.
Remember, if you plan to keep easy plants in a low-light setup, fertilizing your planted aquarium may be unnecessary. I would recommend feeling out your tank for a while to see how growth is before dosing.
Step 5: Adding Fish to Your Planted Tank
Planted aquarium or not, adding fish is always a big milestone. Please do not rush this step.
Even though plants sometimes help speed up the cycling process, it still isn’t an instantaneous process (usually takes 2-3 weeks).
Ammonia and Nitrites should read zero before any live fish are added. Pick up a API Master Test Kit and test often! Check out our fishless cycle guide if you need any more info on the subject.
Once your planted aquarium is completely cycled, it is time to add fish.
Recommended Fish for Planted Aquariums
Here are some of the most popular fish choices when setting up a planted aquarium:
- Tetras: Tetras are great because there are TONS of different species. They are active, colorful, and really bring a planted aquarium to life. Tetras should be kept in groups of 6 or more since they are naturally schooling fish. Neon, Black Neons, and Rummy Nose Tetras are small, hardy, attractive editions to any planted aquarium.
- Corydoras: Cory Catfish are one of the most peaceful freshwater fish available. These bottom-dwellers are the perfect community fish and eat a variety of foods. If I could only recommend one fish, Corys would take the prize. Like Tetras, Cory Cats tend to be happiest is groups of 6 or more. They’re also partial air-breathers, rushing to the surface for gulps of oxygen before swimming back to the bottom!
- Gouramis: Like Tetras, Gouramis come it tons of different colors and sizes, from rainbow colored Dwarf Gouramis to giant Kissing Gouramis. They tend to be very peaceful fish and are great for any community tank. Like the Bettas they’re related to, they can be aggressive towards each other on occasion. With their long, flowing sensory fins, try not to keep Gouramis with anything that nips fins like barbs, as this stresses them out easily.
- Swordtails: One of the easiest-to-keep species on our list, Swordtails are beautiful livebearers that can liven up any tank with their diversity in colors, moderate size, and breeding displays. They are known to reproduce very quickly, so take that into consideration. If breeding and caring for baby fish is of any interest to you, any sort of livebearer is a great choice! Platies, Guppies, and Mollies are other livebearers that will breed just as easily as Swordtails if they’re happy.
- Angelfish: One of the most popular freshwater fish, Angelfish make great inhabitants for any community aquarium (20 gallons or larger). They are beautiful, (relatively) peaceful, and tend to leave plants alone. In fact, they evolved their long, thin profiles to slip among Amazonian plants. As a result, they need plants to feel comfortable (and even to lay their eggs) or they’ll feel exposed and stressed out. Don’t keep adult Angelfish with small Tetras, as once they get larger they’ll eat anything that can fit in their mouths.
- Dwarf Algae Eaters: These little guys aren’t the prettiest to look at but work incredibly hard at keeping algae growth off leaves, rocks, and glass. They also stay small, less than an inch long, unlike their more popular and gigantic relatives, the Plecos that everyone seems to love until they outgrow their aquariums and start knocking over and eating plants!
There are some critters you should actively avoid in the planted aquarium. Pacus are not only voracious vegetarians but also grow foot-ball sized or larger.
Many species of medium to large Cichlid love nothing more than digging and uprooting plants are they carve their territories.
Crayfish and many snail species will devour and destroy plants indiscriminately. Make sure you do your research before straying from the list of species above.
Step 6: Maintaining a Planted Aquarium
You have your substrate laid down, plants in the medium, water topped off and warmed, fish happy and swimming about.
How do we make sure our planted fish tank continues to thrive and prosper?
We need to pay close attention to things like water chemistry, nutrient intake, and plant maintenance to ensure everything stays lush and green.
Keep in mind that over time, your substrate will mix if you’re using different grain sizes. A mix of sand and gravel will eventually become a layer of gravel on top of sand.
Most people use a siphon hose to gently probe and remove fish waste, uneaten food, and other material during a water change. In the planted aquarium, we still do this, only…Less so.
In fact, some aquarists stick to only taking water from the top and not touching the substrate at all! This is recommended only for fully mature setups, by the way.
The substrate is such an important component of the planted ecosystem, it can’t be overemphasized how careful we want to be about messing with it. It’s where plants eat, water is filtered, toxins broken down, and life thrives.
But until our beneficial bacteria and plants mature , we want to gently turn over the substrate to ensure material mixes and plant roots are undisturbed.
Gently turning your substrate during a water change is the best way to ensure not only a healthy, attractive mix but keeps anoxic areas from forming.
Anoxic pockets are spots where no oxygen flow reaches.
Anaerobic bacteria (those that don’t require O2) can thrive there and create especially toxic byproducts that then leach back into your ecosystem. The key word here is “gently,” by the way, so as to avoid damaging sensitive root systems.
Algae is a constant enemy to aquarists, especially in newly set up planted tanks.
This is because there’s an abundance of light and free-floating nutrients but the new plants and beneficial bacteria aren’t able to take it up yet.
Algae are single celled plants that can quickly divide and soak up the available nutrients and form ugly green coatings on any surface available.
Algicides like API Algaefix are a great, if sometimes temporary, means of keeping algae under control.
If you have a localized algae infection, like a patch of blue-green algae (cyanobacteria) on the substrate, hitting it with a dose of hydrogen peroxide is a great tactical nuclear option that won’t cause much harm to the rest of your ecosystem.
Algae eaters are a commonly used and great biological control method for green algae.
Dwarf algae eaters, as mentioned earlier, are model citizens for the planted tank, working hard to keep glass and leaves clear of algae.
Amano shrimp are easier to find nowadays as well! These tiny shrimp prefer to live in groups of 6 or more and will work tirelessly at picking leaves clean of algae. Just remember to keep them away from angelfish and other nippy fish who will see them as food!
Carbon Dioxide Supplements
Carbon Dioxide (CO2) supplementation is one of the best things you can do for your planted fish tank.
While it can sometimes involve additional equipment, this combined with a rich substrate and strong lighting is like rocket fuel for plant growth (and algae – careful!).
You have the following choices for supplementing your planted aquarium with CO2:
Supplements like ISTA CO2 tablets are one of the easiest and least expensive ways to get a boost in plant growth. Simply drop them in and watch them fizz!
One problem with these is that the boost is extremely temporary because most of the fizzy CO2 bubbles end up rising to the surface of the water and dissipating into the air!
One way you can get the most CO2 for your dollar is to place a small plastic cup or other concave surface over the tablet.
As it fizzes, a bubble of CO2 will collect underneath and slowly dissolve additional CO2 into the water over time.
These are a bit more complicated and not really recommended for your very first planted tank.
These include diffusers that hook up to pressurized canisters of CO2 you can buy for a short boost of super tiny bubbles as well as other methods like liquid CO2 injectors.
In short: specialized tools for intermediate and advanced planted aquarium keepers. But if you’re looking to experiment with CO2, you can actually make your own yeast-powered reactor from a coke bottle, dry yeast, sugar, and a few extra tools!
For fishtanks under 30 gallons, these are a neat way to get a CO2 boost cheaply! I’ve done this myself and it’s loads of fun.