40 Gallon Aquarium Setup – Step By Step Guide

Setting up a new tank can be hard work, but the rewards of keeping a freshwater aquarium are numerous. From helping to relieve stress to the joy of watching the amusing antics of colorful creatures, the work is well worth it. We think a 40-gallon tank is a fantastic option as it is big enough to give you plenty of stocking options.

However, it’s still small enough to be very manageable and fit in most homes. It is also versatile in that the entire setup is relatively inexpensive, or you can max your budget if you so choose.

40 gallon aquarium
40 Gallon Aquarium – Source

In this article, we will take you through setting up a 40-gallon aquarium in just 4 easy steps.

  1. Planning
  2. Tank Prep
  3. Setup
  4. Adding Fish


neon tetra aquarium
Neon Tetra Aquarium – Source

Inadequate planning is the downfall of many who are new to the fish keeping hobby. It’s natural to be excited about your new aquarium. Who wouldn’t be? But don’t let your enthusiasm sweep you away. It’s essential to plan out your tank at the very beginning to ensure success, even before you start making purchases. 

Tank Purpose

What is it you want from your tank? Are you looking for a decorative showpiece, an underwater garden, or to breed baby fish? Would you like something colorful, active, or tranquil? Maybe you want something with just one or two big, showstopping fish. Next, consider maintenance. Do you want something that requires a lot of support or something you only have to check every week or two?

Once those decisions are made, you need to think about what type of fish will suit what you want. If you’re looking for ideas on creating a beautiful aquarium, check out our guide!

Tank Shape

40-gallon tanks commonly come in two varieties, the 40-gallon ‘long’ or ‘regular’ tank and the 40-gallon breeder tank. The breeder is shorter, more square-shaped, and, as the name implies, is a better environment for breeding. Many aquarists find the regular tank to be better for display, making it the more common of the two. 


Be sure to research your chosen fish carefully. Some species are territorial and aggressive, so it’s imperative that you want individuals who can cohabitate. Some get along just fine with their own kind, while others are only happy alone or with other species. 

A general rule of thumb in fishkeeping is to keep no more than 1 inch of fish per gallon of water in a community tank. So, for a 40-gallon tank, plan on 40 or fewer inches of fish. For example, you can comfortably fit 20 Cardinal Tetras in a 40-gallon as they will reach 1½ – 2 inches long. With more aggressive fish, make sure to research how much space they need. Sometimes even small fish need a lot of tank space if they are territorial, so the 1 to 1 ratio does not apply.


You also need to make sure that everything in your tank requires the same type of habitat. Some fish prefer densely planted tanks, while others like rock formations or driftwood. Some like coarse gravel substrate, while it will hurt the delicate features of others. Additionally, everything that lives in your tank, both plants and animals, will need to be able to live in the same water parameters. 


Next, you will need to decide the type of equipment you’ll need. Again, researching the type of fish you will keep is essential for this step. You’ll need to know what kind of water current your fish needs. There are many options for water movement and filtration, so make sure to do your homework to find out which will work best for you. Most fish and plants also require lighting to grow happy and healthy, so make sure to look into that, too. Many freshwater fish come from tropical regions, so it’s a good idea to invest in a quality heater. Heaters can either be submersible, hang on the back of your tank, or run unseen through a cable under your substrate. You can either buy one that is specifically tailored to heat to certain levels or one that has an adjustable heat setting.


Finally, you will need to decide where to put your tank to make sure you have enough space in your home. Placement will also depend on your chosen filtration system. If you select a filter that hangs over the back of your tank, make sure to allow enough space between your tank and the wall. Five inches is generally enough, but make sure to measure double check by measuring your filter before adding anything to the tank. It’s also a good idea to have an idea of where your plants and decorations will go inside the tank. It will help to know how much you’ll need when it comes time to purchase these items.

Tank Prep

tank prep
tank prep

Once you’ve finished the planning stage, it’s time to roll up your sleeves and get to work! Once you have your tank, you’ll need to clean it and check for leaks. This is a good idea for both new and used purchases. With a new tank, all you will need is to wipe it down with a little vinegar and some paper towels.

For one you’ve acquired second hand, use a new sponge, vinegar, and some salt to scrub it out. Never use any household chemicals in your tank, and be sure to take special care if your tank is acrylic. They scratch very easily. Make sure to rinse thoroughly after cleaning. 

Next, fill it up with water. This isn’t going to be the water you use for your fish. This step is to make sure all traces of the salt and/or vinegar you’ve used is washed out and to check for leaks. This is an essential step for new aquariums too. There’s no telling if your tank has been damaged when shipped to the store or your home.

Let the water sit for at least a few hours to make sure there are no small defects in the glass and sealant. If you do discover any leaks, learn how to repair them on this guide. Once you are satisfied, empty the tank and dry it out with paper towels or microfiber cloths.


The amount of substrate you will need varies widely and depends on several factors. First, the type of fish and plants you stock need to be considered. If you have no plants and the fish are happy with anything, a thin 1-inch layer is enough to make your aquarium look beautiful. However, if you plan to keep live plants, you will need at least 2 inches to ensure the plants will stay put and form a proper root system, although 4 is optimal.

You will often see aquariums that have a higher layer of substrate at the back than the front. This creates a slope that adds depth to the scenery and provides more room for plants to root. It also reduces the cost since you won’t need as much to achieve the required inches for planting. Burrowing fish need at least 4 – 6 inches of substrate to dig around in, while non-burrowing species require far less. 

As substrate is usually sold in pounds, it can be difficult to calculate on your own how much you will need. For example, 50 pounds of gravel versus 50 pounds of sand will create much different depths because of the difference in grain size. This problem is amplified if you want to use different types of substrate for different areas of your tank. If cost isn’t an issue, it’s a good idea to buy more than you think you will need so you can add substrate as you go to achieve the desired depth.

There are several calculators available online that can help you when determining how much you need, such as this one, or this one. As a general estimate, one pound of gravel or 1½ pounds of sand per gallon will result in around 1½ inches. So, with a 40-gallon tank, you will generally need 40 pounds of gravel or 60 pounds of sand for a starting layer of substrate.


The term hardscape refers to rocks, driftwood, tree roots, and other non-plant decorations. If you don’t plan on using any of these things, you can skip this step, but most freshwater aquarium fish are happier with some sort of decoration. Mimicking their natural habitat is essential to some species, so researching the type of hardscape they prefer is recommended.

You can purchase these items online, at any dedicated fishkeeping store, or even get them for free around your yard. It’s easiest to buy pre-treated items from a fist store, but preparing them at home can be rewarding. If a scavenger hunt isn’t for you, this option containing 17 pounds of rock is excellent for a 40-gallon tank. Whether you buy or find it, make sure that any hardscape you plan on adding to your aquarium is properly cleaned and treated.

This article is great for learning how to prepare wood in preparation for your aquarium, and this one gives valuable advice on rocks.


Aquarium setup
Setup aquarium – Source

Now that your tank is clean, it’s ready to move into position and start adding things. First, set up your stand and tank where you’ve planned. Make sure to leave enough space behind it for equipment and wiring. Next up is to add your substrate. 

If you’ve purchased a substrate that needs to be rinsed, this is when you will need to do it. Some kinds come with beneficial bacteria that are not meant to be rinsed. Others need a lot of washing to remove particles and dust. If you need to wash it, use a clean, 5-gallon bucket. Fill the buck ¼ full, insert a water hose deep into the substrate, then turn on the water. The amount of time needed to wash substrate varies depending on type and brand. Continue agitating the substrate with the water on, until the overflow is mostly clear. Do not let rinsed substrate sit around as this can cause harmful bacteria to grow. Add it to your tank immediately.

Arrange the substrate in a way that is attractive to you, and that allows the depth needed for your setup. Then, arrange your hardscape. Next, add water. You can use a ceramic plate or bowl to pour the water onto to make sure your substrate and hardscape arrangement doesn’t go awry. I’ve also seen aquarists drape a loose layer of plastic wrap over their hardscape to disperse water, but I prefer to use a small plate. 

Next, add your hardware to the tank, but do not turn it on.  Fill the aquarium halfway, then place your plants. Make sure to bury the roots deep enough so that they won’t float up when wholly submerged. Then, fill the aquarium up the rest of the way. Turn on your equipment and ensure all components are working correctly. Next, add water treatment to make your water safe for freshwater fish and plants. If you’re unsure of how to do this, check out this guide.

Adding Fish

Adding fish
Adding fish – Source

A new aquarium setup is very exciting, but cycling your tank before adding fish is very important. Giving the aquarium time to develop beneficial bacteria that are essential to the health of aquarium animals is a must. There are many different ways to cycle a tank. Some take relatively short, while others are quite long. In general, more extended methods are the most effective. However, we understand that looking at a fish tank with no fish for weeks or even months can be frustrating. Be sure to check out our guide that offers different cycling methods so you can choose the one that’s right for you.

Once your tank is adequately cycled, you can start adding fish. Start with adding your smallest and most peaceful species. This helps shyer fish feel comfortable in their new home. Always add only a few fish at a time. If you want to keep something like a large group of Neon Tetras, it’s best not to add them all at once. This can cause spikes in your water parameters, which can be dangerous. Once small and peaceful fish are comfortable, you can start adding bigger or more aggressive species. Adding the most aggressive fish last helps to keep them from claiming the entire tank as their territory and reduces the chance of them harassing other tankmates.


Beautiful aquarium
Setup Aquarium – Source

Now you are ready to start on your dream 40-gallon aquarium. With a little patience and hard work, we know you will give your finned friends the best home possible. We hope this guide has been helpful! If you have any questions or comments, feel free to drop them below.

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