How To Stock An Aquarium – A Beginner’s Guide

When it comes to stocking an aquarium, there’s a lot to learn. Depending on your desired fish and level of experience, the way you stock your tanks will likely change over time. However, if you’re just starting out, you’ve come to the right place.

Below, we’ll detail all the basics of how to stock an aquarium from scratch. With a few quick pointers, you’ll be able to host happy, healthy fish in no time at all. Though mastering the art of fishkeeping can take years to fully understand, you can set up your first basic tank using this aquarium startup guide. 

Deciding Your Fish Type

Before you start looking for any supplies, it’s important to determine what type of fish you’re looking for. This will predetermine your water type, substrate, and general tank strategy, so it’s always best to start here for the most flexibility.

In general, fish and tank type can be broken down into 4 main categories:

  • Freshwater Cold 
  • Freshwater Tropical
  • Marine Cold
  • Marine Tropical 

As you can see, the first identifier (Freshwater vs. Marine) determines the water type or salinity level. The second identifier (Cold vs. Tropical) refers to the preferred climate or thriving temperature of certain fish. 

If you’re just starting out, it’s generally wise to stick with freshwater fish types. This is because these fish are usually more tolerant of stark water changes. While you iron out your expert fishkeeping skills, these fish will stay strong since they’re more prone to adapt. 

As you learn more about best fishkeeping practices, you can expand your reach to other types of fish and tanks. Some common freshwater fish varieties include Goldfish, Neon Tetras, Guppys, Glasscat, and Angel Fish. 

Placing and Sizing Your Tank

When it comes to picking out your starter tank, you may be tempted to choose the most compact variety you can find. After all, it stands to reason that you’ll probably only want to start out with one or two types of fish until they’re all well adjusted.

However, keep in mind that smaller tanks can promote dynamic water changes that can be hard on your fish. Larger tanks are usually more stable since it takes water a longer amount of time to disperse throughout the entire tank. Therefore, it may be wise to look for a larger tank to protect your fish while you’re still learning how to properly take care of your aquarium and fish. 

When choosing between plastic or glass, you’ll have to think about your priorities. While a plastic tank may be easier to move around your property, it can also be easier to scratch. Glass tanks can be heavier, but they are also easier to see through, which can make for more accurate tank monitoring. 

For exact measurements, you can refer to this simple aquarium size chart. The chart is based on gallon measurements and will let you know how heavy you can expect a tank to be when filled. It should be noted, however, that you should only attempt to move an aquarium tank once it is emptied.

The chart is perfect for reference, and also allows you to thoughtfully consider where your tank should be placed. You’ll want to make sure that your tank is placed on a large, flat surface without excess light.

Too much light can promote the growth of unwanted algae, which can make it difficult for your fish. However, it can be helpful to look into purchasing a special tank light for your tank, as some freshwater and tropical fish thrive with additional light. 

Before going out to buy additional equipment, make sure that your aquarium is properly supported and level. Try to stick to a larger tank if you can as you learn the art of fishkeeping. 


Finding Your Essential Equipment

Once you’ve selected the appropriate space and size of your aquarium, you’ll want to start selecting essential equipment for your aquatic ecosystem. 


After you place your new tank, you’ll want to start thinking about gravel. Gravel, which is sometimes referred to as substrate, should be purchased directly from a trusted aquarium shop or online store. Normal gravel is sometimes coated in harsh chemicals that can directly harm the state of your fish. 

If you have the option, pre-washed or fully coated gravel is ideal. Unless you have a sub-gravel filter, this will be the first layer in your tank. The substrate should be arranged so that it has a slight slope towards the front of the tank with a depth of about 2 cm at the front of the tank, to 6 cm in the back. This can make your cleaning process easier by naturally encouraging debris to come towards the front of the tank. 

You can also purchase colored gravel to match the theme of your aquarium. Just make sure that it’s crafted specifically for fish so that your tank stays healthy. 

Filtration System

You’ll want to make sure that your filtration system is properly installed before adding other elements to your tank. This is one of the most important parts of your aquarium, since it will help regulate the water quality and therefore keep your fish healthy. 

Generally, you’ll be choosing between a sponge, canister, undergravel, sump, or pump-style filter. The best pick for your aquarium will vary depending on the size of your tank along with the type of fish you plan on hosting. 


You’ll also want to make sure you install your basic heater or heating element before you add in any water, tank furniture, or fish. After the water is put into the tank, turn on the heating element to the desired temperature, and give the water time to reach equilibrium. 

Always make sure to only turn on the heating element when there is water present in the tank for the best results. If you have a bacteria starter, you can add this in shortly after the heating element. 

aquarium fish


Especially if you have a heating element, you’ll want to have a reliable thermometer in your tank. This will make it easy for you to monitor your tank’s health at a glance which is vital for both your fish and aquatic plants. 

Water Conditioner

Before adding tap water to your tank, you will need to properly condition it. This is because tap water usually contains too much chlorine to be viable for fish. Follow the instructions printed on your water conditioner bottle for the best results. Also, be sure to let the water rest for some time so that it can settle before adding fish to the mix. 

Fish food

When it comes to picking out fish food, find a variety that’s well suited to the type of fish you’re looking for. Any worker at your local aquarium shop should have some recommendations. When it comes to feeding, try to only give your fish as much food as they can eat within about 5 minutes in one sitting. 

Your fish will likely eat less than what you would expect. In fact, a fish’s stomach usually ends up being about the size of its eye. Therefore, you definitely want to be careful about not overfeeding your fish as they may eat less than what you may expect. 

After your fish eat, you’ll want to remove any uneaten food after your fish finish eating. Uneaten food can easily pollute the water which can adversely affect the entire tank. 


You’ll want to make sure you have a good quality fishnet on your side so that you can properly transfer your fish from one location to another. 

Water Test Kit

It’s immensely important to get in the habit of regularly testing your water quality. The key things you’ll want to look out for are ammonia, nitrite, nitrate, and pH levels. While most of these values will be balanced with a high-quality water filter, you should also have some test strips on hand to get an accurate reading as needed every 2-3 days. 

endler tetra

Rocks, Plants, Decor

Make sure that any aquarium decor or furniture you add is made for aquatic life specifically. This will ensure that your tank stays healthy and that you don’t inadvertently add unnecessary chemicals to your tank environment. Even so, make sure to thoroughly rinse any physical addition to the tank before placing it in the aquarium. 

You should allow aquatic plants a period of about two weeks to settle in the tank before introducing your first set of fish. 

Adding In Fish 

Finally, for the fun part! Once your tank is properly situated and primed for its first inhabitants, you can gradually start to introduce fish to your tank environment. This process should be slow, calculated, and done over a period of about four to six weeks. 

You’ll want to pick out the healthiest fish you have for the initial inhabitants. These fish are likely well suited to deal with dynamic changes and will set your tank off on the right foot. Plus, by adding in fish gradually, you also give your tank as a whole a chance to adjust to the introduction of new bacteria and waste. 

If your fish are currently bagged, allow the bag to sit in the tank’s water for about 10 minutes or so ensuring that the temperature is properly equalized. Next, you can gradually open up the bag so that your fish gets used to the tank’s water for an additional 10 minutes. 

Finally, you can use your fish net to remove the fish from the bag and fully introduce it to the tank. Make sure to discard the original bag, and monitor your fish’s health carefully over the next couple of days to ensure that it is adjusting properly. 

While you continue to introduce fish to the tank, consider distracting the resident fish by feeding in a separate corner of the tank. This will make the transition as easy as possible for both new and resident fish. 

Before you consider adding new fish to a tank environment, do your due diligence by researching each breed thoroughly. Not all fish breeds are compatible, so taking the time to look into each fish breed’s needs is vital to the overall success of your tank. 

In addition, it’s best practice to allow fish to remain in a quarantine tank for about 4 to 6 weeks before transferring to an aquarium with other fish residents. This will give you time to see that the new fish is healthy, and reduce the risk of adding unwanted contaminants to your entire tank. 


Basic Maintenance

When it comes to basic aquarium maintenance, there’s a lot of ground you need to cover. At the very least you want to make sure that you focus on routinely changing the water about 25-50% every week to two weeks to keep everything properly balanced.

This will also make it easier for you to keep your tank fresh for longer periods of time before a thorough tank cleaning. You’ll want to test the water for the following parameters:

KH (Carbohydrate Hardness)>4.5dH (80ppm)
*If any Nitrites are detected, test for Ammonia

While generally you’ll want to check these values every other week, it’s probably safest to check them more frequently, especially when you’re just starting out. 

Be sure to check out our article on thorough tank maintenance for more information.

Stocking An Aquarium Properly Takes Time

Learning how to stock an aquarium properly takes time and consistent effort. Remember that becoming a master fishkeeper doesn’t happen overnight. That being said, everyone has to start somewhere, and using the keep points above, you’ll have a successful tank up and running in no time at all. 

Take the necessary precautions by starting with more resilient fish types and checking your water more frequently than what’s usually recommended while you’re just starting out. With patience, you’ll be able to upgrade to more advanced fish and tank systems in time. Enjoy crafting a starting tank system that’s entirely your own. 

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