In short
- A new tank is not ready for fish on day one: the filter needs time to grow the helpful bacteria that break down waste, a process called cycling.
- Decide which fish you want first, because the species sets the tank, the equipment and the water conditions they need.
- A test kit shows you what is happening in the water long before the fish do.
- Add fish a few at a time and feed lightly, because a young tank copes with only a little at once.
A first aquarium looks like a shopping job: tank, filter, fish, done. In practice it is closer to a small garden. You build the setting, wait while it settles, and only then bring in the animals. Fish can struggle in water that looks perfectly clear. This guide covers the equipment, the waiting period that keepers call cycling, and how to add fish slowly. It gives no sizes, temperatures or stocking numbers, because those depend on the species; take them from the equipment instructions and from someone who keeps your chosen fish.
Choose the fish first, then the tank
It works better to pick the fish before the tank. Freshwater fish differ in how much space they need, what water they do well in and which company they tolerate. Some are peaceful, some nip at others, and some grow far larger than they look in the shop. Read about the species you like, ask an aquarium specialist or an experienced keeper, and write down what each needs before you buy equipment.
Water is heavy, so a full tank needs a stand or a piece of furniture made to carry that weight, on a level floor. Place it away from direct sunlight, which feeds algae, and away from drafts and radiators. In general, a larger volume of water changes more slowly than a small one, which gives a beginner more time to notice a problem. How large is right for you still depends on your space and your species.
The equipment, in plain words
| Item | What it does | What to check |
|---|---|---|
| Tank and lid | Holds the water; the lid keeps fish in and dust out | A lid with room for cables and feeding |
| Filter | Moves water through a material that catches debris and houses helpful bacteria | Whether the maker's rating suits your tank volume |
| Heater and thermometer | Helps keep the water temperature steady; the thermometer lets you check it | Whether your species need a heater at all; the instructions on when it may be switched on |
| Lighting | Lets you see the fish and feeds live plants | Lights made for aquariums; a timer helps |
| Gravel or sand | Covers the bottom and holds plants | Rinse as the pack says |
| Water conditioner | Used to make tap water suitable for fish | Many tap supplies contain disinfectants; follow the label |
| Net, bucket, test kit | Moving fish, topping up and measuring the water | Keep the net and bucket for the aquarium only |
Filters sit inside the tank, hang on the back, stand beside it in their own container, or work as sponges driven by an air pump. All do the same basic job, so choose by tank volume, room and how easy the cleaning looks. Keep the filter running once fish are in, because the bacteria in it need a steady flow of water.
Fish like places to hide, and plants and decor provide them. Live plants take up some of the waste in the water, while artificial plants need no light and little care beyond a rinse. Rocks, wood and ornaments should be made for aquariums and have no sharp edges that could snag fins. Items from the garden or a craft store may release things into the water, so leave them out unless the maker says they are meant for aquarium use. Browse the Fish and Aquariums section to see the kinds of equipment that exist, or use the fish filter to narrow the whole shop.
Set it up in a sensible order
- Place the empty tank on its stand and check that it is level before any water goes in.
- Rinse the gravel or sand, and any rocks or decor, in plain water with no soap, then arrange them.
- Fill the tank with tap water treated with conditioner, following the label.
- Install the filter and heater following their instructions. Many heaters must be fully covered by water before they are switched on, so read the manual.
- Add plants, set the lights on a timer, switch everything on and check for leaks.
Water and electricity need respect. Keep plugs and sockets above the water line, and let each cable hang in a low loop before it rises to the socket, so that drips run off the loop and not into the plug. Unplug equipment before you put your hands in the tank or move anything.
Why a new tank must be cycled
Fish make waste, and so do leftover food and decaying plant matter. As these break down they release ammonia, which is harmful to fish even in small amounts. In a settled tank, helpful bacteria grow in the filter material and on surfaces, and they turn ammonia into nitrite, which is also harmful, and then into nitrate, which is much less harmful and is removed by partial water changes and taken up by plants. This chain is the nitrogen cycle. A brand-new tank has almost none of these bacteria, so if fish go in at once, ammonia can build up faster than anything can deal with it.
Cycling means giving the bacteria time to establish before the fish arrive. Keepers do this by adding a source of ammonia in small, measured amounts, following the instructions on the product they use, and testing the water as the readings rise and fall. There are several methods, which an experienced keeper can describe. Expect it to take weeks rather than days. A clear tank is not a cycled tank, because water can look perfect while ammonia is still present.
Testing the water
A test kit measures ammonia, nitrite and nitrate, and comes as liquid reagents or as strips. Follow the instructions closely, since small differences in the amount of water or the waiting time can change a reading. During cycling, test every few days and write the results down. As a general pattern, a cycled tank shows ammonia and nitrite at zero while some nitrate appears. Most kits also measure acidity (pH) and hardness. Different species prefer different values, so check what yours needs before you change anything.
Adding fish slowly
When your tests show a cycled tank, add a few fish, not a full community. The bacteria grow to match the amount of waste, so a sudden jump in waste can outrun them. Test again over the following days and feed lightly. Uneaten food rots and adds to the waste, so offer only what the fish finish in a short time, as the food label suggests, and remove the rest. Ask the seller how to introduce new fish, and check that the species suit each other before you mix them.
Routine care is simple but regular. Change part of the water, using treated water close to the tank temperature. When you clean filter material, rinse it in water taken from the tank and not straight from the tap, and do not clean everything on the same day, because the helpful bacteria live on those surfaces. Look at your fish daily. If something seems wrong, ask an aquarium specialist or a vet who sees fish, and do not add treatments on a guess.
If a quieter, smaller companion appeals more than fish, our journal piece on making a home for a small pet or a bird covers the basics of housing them.