Beginner's Guide to 20 Gallon Planted Tank Lighting

Beginner’s Guide to 20 Gallon Planted Tank Lighting

At first glance, tank lighting might feel like nothing special. But there’s a catch-

Lighting is super-sensitive when it comes to a 20 gallon planted tank. And guess what? One wrong move and you’ll see the whole setup crumbling down.  

So, what are the things you should know about a 20 gallon planted tank lighting?

For starters, you need to understand why lighting is important. Then you have to make a budget for buying the light according to your tank size, light intensity, and light type. Last but not the least, you need to know how to set up and use the light you’ve bought.

Now, this is just a tiny snippet of our in-depth guide. Stick with us for 3 more minutes to get a detailed overview of everything related to 20 gallons tank lighting.  

Now let’s shine right through the details-

Things To Consider Before Buying Planted Tank Lighting

Well, my friend, you need to consider a few things before you set up your 20 gallon planted aquarium lighting

You see there are a few key questions that will determine your planted tank setup. So, what could those questions be? 

It’s okay if you’re feeling blank at this point. We felt like that too. So, we’ve summed up all the determining factors into five key questions. Now, let’s get through those, one by one- 

Do You Have CO2 Injection?

CO2 is the most important element for a planted tank. Now, your plant won’t generate tons of CO2 all by itself. For a successful planted tank, you need to inject CO2, for example, API CO2 Booster

Now, what are the benefits of injecting CO2?

If you inject CO2, you’ll be able to have bright lighting and beautiful growth in the tank. Your plants will thrive for a longer time. Sometimes 20 gallons planted tank CO2 injection isn’t needed. For example, if you’ve got a 20 gallon low-tech planted tank then you might not need a CO2 injection.

Because plants in a low-tech tank don’t necessarily need a CO2 injection to grow. 

If that’s the case for you, you can forget about the CO2 injection and just proceed to buy a good light

Is the Light Intensity Same for All the Plants?

Install LED Lights in Aquarium - Build My LED


When it comes to lighting you might get to see the term ‘lumen’ a lot. Many of you might already know about this. 

But again let’s explore this so that we stay on the same page. So, what is a lumen in lighting? Lumen is basically the total measurement of the visible light emitted by a specific source per unit of time. The higher the lumen the brighter your planted tank will appear.

In the indoor gardening world, people normally use lumen per square meter and lumen per liter of water to measure the light level/brightness.

Now there’s another very important term that you’ll come across which is PAR. So, what does PAR mean? 

Well, PAR or photosynthetic active radiation is the measurement of light emission within the photosynthetic range of 400-700nm. Plants use this photosynthetic range to grow. 

Let’s try to gain some more knowledge about lighting, shall we?

To be honest, the intensity of light varies from plant to plant. In the aquatic world, we’ll find different types of plants. However, if we divide them according to intensity then there are three types of plants. 

For you, we’ve discussed both the plants and the amount of lighting they require down below-

Do you find all this information very confusing? 

Well, don’t worry my friend. We’ve got your back! For you, we’ve also given the intensity of the light according to the number of gallons. 

So, just go through the table below-

Aquarium/planted tank typeLight amount(watts per gallon)
Freshwater planted tank2-5
Freshwater reef tank4-8

Now you have the proper knowledge about the amount of light you need to provide the plant you choose.

Also, keep in mind that the plants will suffer if this number goes a little here and there. That’s why my friend, we suggest you use a light meter to measure the light intensity in your 20 gallon tank

We’ve recommended some light meters for plants that you should check out-

What Color Light Should You Buy?

Yup, you heard it right. Color or spectrum is a very important factor while looking for light. Why may you ask? 

Well, in the above segment you’ve seen the discussion on PAR. The 400-700nm range we talked about actually carries several colors. And these colors are essential for the photosynthetic process of your plant. 

For that reason, you must gain some knowledge about this.

Photosynthetic Action Spectrum

As you can see, this picture refers to the relative photosynthetic rate of plants. So, what color light is best for a fish tank?

However, plants need the colors green and yellow as well. These two aren’t useless. That’s why a full spectrum light works best for a planted tank.

Now as we’re talking about lighting, the temperature automatically comes into the picture. 

Do you know the ideal temperature for a planted aquarium?

Well, it’s around 76-80 degrees Fahrenheit. A simple rule of thumb of providing the right temperature is providing the right color and amount of light.

Frankly speaking, there’s a lot more to know about wavelengths and spectrums. But we don’t want to tire you with all the technical stuff. Because knowing the basics we’ve provided is enough for growing plants. 

What Should be the Length of the Light?

Now, let’s come to the length of the light. Obviously, you can’t use a 72 inch LED planted aquarium light for a 20 gallon planted tank. Because that’s just absurd. A person that has a 125+ gallon tank like 150 Gallon Starfire Glass Aquarium can only use such a big 48″-54″ LED light

That’s why you need to keep in mind the dimensions of your 20-gallon tank and make a budget according to that. 

We like making things simpler for you. So, on that note, we’ve given the tank dimensions.
The size of a 20 gallon long planted tank and a 20 gallon high planted tank-

Now you have the answer to the question- what size light for a 20-gallon fish tank? If you’ve got a 20-gallon long tank, you have to use a light that is 24 inches long. And a 30 inches long light for the 20-gallon high one.

You might ask- why 30 inches led aquarium light? If you do so, your tank will get the maximum coverage of light or photons. No one in your tank will be light-deprived! 

Sometimes, it’s hard to keep the floating plants in one place. That’s how the light gets blocked and the planted aquarium plants don’t get a sufficient amount of light. This can be a problem. So you might want to choose the length of your light wisely.

Which Type of Light Do You Want?

Understanding Freshwater Aquarium Lighting


By now you’ve collected lots of information about lighting, right? 

On that note, you should know that lighting for 10 gallons planted tank and a 20 gallon planted tank isn’t similar. Because you can use a normal or small bulb for your 10 gallons. But when a 20 gallon comes into play, things get interesting. 

Now, you’ll see different types of planted tank lighting out there. But here we’ve mentioned the most popular ones for your 20-gallon tank-

T5HO Light

T5HO is a thin high-output fluorescent tube that is 5 or 8inch in diameter. T5HO lights are available in 24,39,54, and 80 watts. These lights come in blue and red colors as well. A T5HO fixture comes in 4,6, and 8 bulbs configurations. 

So, should we use t5ho aquarium light?

We suggest using the 4 bulbs T5HO(ATI) fixture for your 20 gallons tank. Because it’s around 24 inches in length. So, it’s quite suitable for a 20-gallon tank. Now for the pros and cons of T5HO-

  • Produces even light with good fluorescence 
  • Great for the growth of the plants
  • Cheaper than other lights 
  • Not long-lasting. Thus, needs to be replaced every one or two years

We’ve recommended some of the best T5HO lights for you-

LED Lights

LED lights are very popular when it comes to planted tank lighting. More than 50% of the people who have planted tanks invest their time and money into LED lights. LEDs also come in a wide range of watts and colors. 

You can use a 24-inch blue LED light for a 20-gallon long tank. Now, should you consider buying LED lights? Let’s look at their pros and cons to help you make that decision-

  • Doesn’t require much energy
  • Comes in different numbers of colors
  • Long-lasting
  • Gives a shimmering effect
  • Low heat output
  • Most models are expensive
  • Only low-tech tank lights are budget-friendly

Some of our favorite and best LED lights for 20 gallon planted tank are-

Now just pick the best light for your light. And then start using it for the proper growth of both your plants and fish. 

How to Get Started With 20 Gallon Planted Tank Light

As you already know a 20 gallon planted tank can either be a 20 gallon long or a 20-gallon high tank. Luckily, the instructions are quite similar for both tanks-

Set up the Light

After buying a planted tank light, the first you need to do is set it up. Now, be extra careful while doing so because we don’t want you to damage the plants or the fish. Though it’s not as complicated as setting up an air-cooled reflector.

Sometimes lights have stands attached to them. So, if you buy a light that has a stand then you can just place them beside your tank.

20 gallon planted tank lighting

However, if the light doesn’t come with a stand then you can hang it by yourself. Now, there are two ways of doing a 20 gallon planted tank setup–  

Firstly, you can either make a shelf to hang the light or hang it from your ceiling. Secondly, you can use a lighting rack to fix the lights around your tank.

We’ve tried out these light hangers for our planted tanks-

That’s not all-

While setting the light up, you need to keep at least a gap of a few inches between the light and the rim of the tank.

For a T5 tube (ATI), the gap needs to be about 10-12 inches and the gap should be 10-15 inches for LED light such as solar RGB.

You can watch the following video to have a practical demonstration of the whole setup and other nitty-gritty –

Keep an Eye on the Light

You can’t keep the light on 24/7. Why?

The answer is very simple! Your aquatic plants don’t need that much light. If you provide too much light then you’ll get a lot of algae growing in your tank. As a result, you’ll not be able to check on the plants or the fishes in your 20 gallon long planted aquarium. This affects the plants and fishes negatively and leads them to an untimely death.

On the other hand, if there’s a lack of light then you’ll face some consequences as well. The leaves of your plants will start yellowing and eventually fall off. Simply put, your plants will die and the fishes will get sick.

The question you want to ask now is probably- what is the right amount of light? 

Well, you know the amount of lighting you should provide. Because we’ve mentioned the amounts before in the segment ‘Is the light intensity for all the plants different?’. So, make sure that you’re just within the range!

After doing that, you need to keep the timing of the lighting in check. For that, you can use a timer with your light.

At the beginning of your planted tank journey, keep the lighting at a minimum. By decreasing the light’s intensity from the beginning, your plants can avoid a strong light causing a shocking phase. 

So, how long should I keep aquarium lights on?

It’s okay to keep the lights on for 12 hours for a high-tech planted tank that has fast-growing plants. But if you want to create a low-tech cold-water tank then keep the lights on for 6-7 hours.

Set your timer according to this calculation and you’re good to go!

Benefits of Planted Tank Lighting

Good lighting can save you and your plant in the long run. By adding light to your 20 gallon planted aquarium you can get two major benefits-

Easy Plant Growth

We all know that light is very important to grow plants. Therefore, if you provide a sufficient amount of light to the plant in your tank, they can grow beautifully. 

Without lighting, your plants and fish will get sick. And you’ll suffer from a nightmare. That’s why please install lighting for your 20 gallons tank!

Enhanced color and beauty

Believe it or not, lighting can make a huge difference for your planted tank. So, if you’re wondering why do you need a fish tank light

20 gallon planted tank lighting

Whether you’ve got a 20-gallon fish tank or planted tank, it will automatically look prettier after setting the lights up. You can see the inside clearly and clean it easily in case it gets dirty. 

If the tank is clean and fresh then you can avoid your plants and fishes having a tough time. Instead, you can see them enjoying and thriving in your tank. 

3 Important Tips 

Now it’s time for some helpful tips after all the detailed information. These will help you with your work regarding the 20-gallon high or 20 gallon long planted aquarium lighting. Therefore, let’s quickly dive into the three important tips-

  • You can get away with using any kind of light for your 20 gallons planted tank. However, using a full spectrum light will give you lots of advantages such as maintaining certain colors of your plants.
  • It’s better to get a light according to the length of your 20-gallon tank. You can easily avoid the yellowing of your plants if you do so. 
  • It’s important to keep the temperature in check as well. If the temperature of your tank crosses 80 degrees Fahrenheit then you’re doomed. For that reason, you can use a thermometer. We recommend using a stick-on type thermometer.

After all this, you can move on to the 20 gallon planted tank ideas. Come up with your own ideas or you can take some inspo from the internet. Moreover, you can add fish to your 20 gallons planted tank for a nice touch. The options and choices are unlimited!


What is the best light for a 20 gallon long planted tank?

You can go for LED lights. You’ll find a lot of 24–30 inch LED lights. You can find lots of good-quality LED lights for your 20-gallon tank.

How long can I keep the lights on?

Well, we’ve discussed this in detail (in the segment: keep an eye on the light). However, the ideal time is 8 hours. You can set your timer according to this time.

Is lighting a very important part of the 20 gallon planted tank setup

Yes, definitely. If you want to grow plants, you’ll need to buy a good light. There are lots of good lights out there so choose a good 24-30 inch light for your 20 gallons. 

How many watts does a 20 gallon planted tank need?

Different types of tanks have different watt requirements. And thumb rule for planted tanks is 2 to 5 watts per gallon for freshwater planted aquariums.


We tried our best to provide you with every possible information on 20 gallon planted tank lighting. We hope you reach a conclusion! 

So which light did you buy for your tank?

Let us know by leaving a comment. Good luck, plant lovers!

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