There is a moment in almost every new fishkeeper’s journey when an empty glass tank is sitting in the room and suddenly there seem to be a hundred decisions to make.
What filter do I need? Do I need a heater? Which substrate should I use? Can I add plants straight away? How long must the aquarium run before I add fish? And why, after watching six videos about cycling an aquarium, do I somehow feel less certain than when I started?
The good news is that setting up a freshwater aquarium really doesn’t need to be complicated.
There are some things you need to get right, but there is also a lot of room for personal preference. Your aquarium does not have to look like somebody else’s, use the same equipment, or contain the same fish. What matters is that you create an environment that suits the animals you want to keep and that you can maintain consistently.
That last word matters: consistently.
A simple aquarium that is looked after properly will generally serve you far better than an elaborate setup that becomes a chore after the first month.
Start with the fish, not the fish tank
One of the easiest mistakes to make is buying an aquarium and only afterwards deciding what should live in it.
Turn that process around.
Before choosing the tank, spend some time deciding what sort of aquarium you actually want.
Perhaps you like the idea of colourful guppies or endlers. You may want a peaceful community aquarium containing several small species. Perhaps shrimp are the attraction. You might be dreaming of a heavily planted aquarium, or you may simply want something attractive and relatively easy to maintain.
Those choices affect almost everything that follows.
The adult size and behaviour of the fish will influence the aquarium size. Their preferred water conditions may determine which species can live together. Some fish need to be kept in groups. Some spend most of their time close to the substrate while others prefer open swimming space. A species that looks tiny in a pet shop may be very different once fully grown.
So before asking, “How many fish can I put in this tank?”, ask a better question:
What do these particular fish need in order to live well?
That single question can prevent an enormous number of problems.
Choose a tank that gives you some room for error
Tiny aquariums can look ideal for beginners because they are inexpensive and appear easy to manage.
In practice, small volumes of water can be surprisingly unforgiving. Temperature and water chemistry can change more quickly, waste becomes concentrated faster, and your stocking options are limited.
Larger aquariums tend to offer greater environmental stability. RSPCA guidance similarly recommends going larger than the minimum required because greater water volume produces more stable temperatures and water conditions.
For many first-time fishkeepers, I think an aquarium somewhere around 60–100 litres is a very practical starting point. That isn't a magic number and it certainly doesn't mean every fish can live in a tank that size. It simply gives you useful flexibility without immediately committing you to a huge aquarium.
Remember the weight as well. A litre of water has a mass of roughly one kilogram before you add the aquarium itself, substrate, rocks and wood. Your 100-litre aquarium is therefore not something to balance on an unused bedside table and hope for the best.
Place it on a level, sturdy stand away from direct sunlight and sources of excessive heat. Direct sun can make temperature and algae management much more difficult.
What equipment do you actually need?
Aquarium shops are extremely good at providing opportunities to spend money. Some of those purchases are useful. Others will eventually find their way into the mysterious cupboard where old aquarium equipment goes to spend its retirement.
For a straightforward freshwater aquarium, your basic equipment will usually include:
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an appropriately sized aquarium and secure stand; a suitable filter; a thermostatically controlled heater if your chosen species require one; a separate thermometer; suitable lighting; substrate if you want it; water conditioner; a water-testing kit that includes ammonia and nitrite; a siphon and bucket reserved for aquarium use; and suitable food for the fish you eventually choose.
Plants, rocks, wood, additional aeration and other equipment can all be useful depending on the aquarium you are building, but they are not universal requirements.
Buy equipment because it solves a problem or meets the needs of your livestock, not because somebody has told you that every aquarium must contain it.
Your filter is doing much more than cleaning the water
Beginners often think of the filter as a machine that catches dirt.
It does that, but its more important role is biological.
Fish produce waste containing ammonia. Decaying organic matter and uneaten food contribute to the waste load too. Ammonia is toxic to fish. In a mature aquarium, microorganisms associated with the biological filter convert ammonia to nitrite and then convert nitrite to the much less toxic nitrate.
This is why filter media is so important. It provides enormous surface area on which those microorganisms can live.
It is also why completely replacing all your established filter media because it looks dirty can create problems. A mature filter isn't supposed to be sterile.
Choose a filter appropriate for your aquarium and its inhabitants. Sponge filters, internal filters, hang-on-back filters and canister filters can all work very well in the right situation. There isn't one filter that is automatically “best” for every tank.
We’ll deal with that properly in a separate guide.
Do you need a heater?
That depends on your fish.
“Freshwater” doesn't automatically mean “tropical”, and “tropical” doesn't mean that every species should be kept at exactly 25°C.
Research the temperature range of the animals you plan to keep and then maintain the aquarium within an appropriate, stable range. Current welfare guidance emphasises species-appropriate temperatures and avoiding sudden temperature changes.
If you are keeping tropical fish in a room where the water would otherwise fall below their required range, use a thermostatically controlled aquarium heater.
I strongly recommend using a separate thermometer as well. Heaters can fail. A thermometer gives you an independent way of noticing that something has changed.
Choose your substrate with a purpose in mind
Gravel, sand, aquasoil and other substrates all have their place. There is no rule saying that every freshwater aquarium needs the same one.
If you're creating a simple aquarium with hardy plants, an inert sand or gravel may be perfectly adequate. Root-feeding plants may benefit from root fertilisation or a nutrient-rich substrate. Some bottom-dwelling species have particular substrate requirements that should be considered before you build the tank.
This brings us back to the principle we started with: decide what you want to keep first.
It is much easier to choose the right substrate for a fish than to discover that the fish you desperately want isn't well suited to the substrate already covering the bottom of your aquarium.
Add plants and cover
I am a big supporter of live plants in freshwater aquariums.
They look good, provide cover, create structure within the tank and give fish places to retreat. Depending on the setup, they can also use nutrients from the water as they grow.
You don't need to begin with a complicated planted aquarium. Species such as Java fern, Anubias and many Cryptocoryne are popular precisely because you can create an attractive aquarium without immediately needing to become an expert in injected CO₂ and advanced fertilisation.
Decorations should also serve the fish rather than simply filling space. Wood, rocks, caves and plants can break lines of sight and provide security, particularly for shy or territorial species.
Just leave enough open space for the fish to swim naturally.
Prepare your water
If your tap water is treated with chlorine or chloramine, it needs to be made safe before exposing your fish and filter biology to it. Use an aquarium water conditioner appropriate for your water supply and follow the manufacturer's dosage instructions.
This is something to repeat during water changes, not merely when the aquarium is first filled.
Your local water chemistry matters too.
Rather than automatically trying to alter your pH and hardness to reach somebody's idea of “perfect” water, find out what comes out of your tap. In many cases, choosing species suited to your available water is considerably easier than constantly trying to manipulate it.
Stable, suitable conditions are far more useful than chasing a particular number because you saw it in a chart.
Now comes the part that beginners really shouldn't skip: cycling
Filling an aquarium with water and running the filter for a week does not automatically mean that the aquarium has cycled.
Cycling refers to establishing a population of microorganisms capable of processing the waste your future livestock will produce.
The simplified version looks like this:
ammonia → nitrite → nitrate
Both ammonia and nitrite are toxic to fish. In an established aquarium, your biological filtration should normally process both so that tests show 0 mg/L ammonia and 0 mg/L nitrite.
For a new aquarium, I recommend a fishless cycle.
That means establishing and testing the biological filter before fish are placed in the aquarium, rather than using fish themselves as the source of ammonia and exposing them to potentially harmful concentrations while the system develops. The RSPCA likewise strongly recommends fishless cycling for new aquarium owners.
There are several legitimate ways to carry out a fishless cycle, including using an appropriate ammonia source and seeding the filter with established, disease-free biological media. Bottled bacterial products are also commonly used.
Don't judge the cycle by the calendar alone. Judge it by your test results.
Aquarium biofilters need time to develop. Exactly how long varies with the system and method being used. This is one of the first useful lessons fishkeeping teaches: biology doesn't care much about our impatience.
We’ll explore the full cycling process in the next guide.
The tank looks ready. Can I add fish now?
Once you have confirmed that the aquarium is cycled and that its temperature and water conditions are suitable for the species you have chosen, you can begin stocking.
Don't turn it into an aquatic version of supermarket sweep.
Add livestock thoughtfully, keeping the eventual adult population in mind. Research how many individuals each species should be kept with, compatibility between species, adult size, swimming behaviour and the amount of physical space available.
A tank may physically hold more fish than it can sensibly support.
Also remember that a newly established aquarium is still young. Stability improves with time. There is no prize for filling every available part of the water column during the first weekend.
Feeding your first fish
New fishkeepers are usually far more likely to feed too much than too little.
I understand why. Feeding is enjoyable. The fish rush towards you and look as though they haven't eaten since the previous Tuesday, even when you fed them ten minutes ago.
They are very convincing.
Uneaten food does not simply disappear. It decomposes and adds to the biological load in the aquarium. Heavy feeding also means more waste from the fish themselves.
Feed an appropriate food for the species you keep and observe what happens. You want the food to be eaten rather than accumulating on the substrate and disappearing behind decorations.
Different species have different feeding behaviours and nutritional requirements, so we'll return to feeding in its own article rather than pretending that one rule works for every fish.
Your aquarium needs maintenance, not constant interference
One of the most useful lessons I've learned from keeping multiple aquariums is that consistency usually beats dramatic intervention.
An established tank doesn't need to be dismantled and scrubbed every weekend.
Regular partial water changes remove accumulated waste and replenish water. The amount and frequency should be guided by stocking, feeding, plant growth and your water-test results rather than treated as an inflexible law. Your original Art's Fish Room guide used a practical starting routine of roughly 20–30% weekly water changes. That remains a perfectly reasonable routine for many normally stocked home aquariums, adjusted where your particular tank tells you otherwise.
Clean visible waste where needed. Trim plants. Wipe the glass. Check that water is flowing properly through the filter.
When filter media needs cleaning, the aim is to remove accumulated debris without sterilising your biological filter. Rinsing reusable sponge or biological media gently in water removed from the aquarium is a sensible approach; avoid washing established biological media thoroughly under untreated chlorinated tap water. RSPCA guidance makes the same recommendation.
Most importantly, look at your fish.
Are they eating? Are they behaving normally? Is somebody hiding who normally doesn't? Is a fish breathing rapidly? Are fins clamped? Is one individual being bullied?
Five minutes spent actually observing your aquarium can tell you a great deal.
A clear tank isn't necessarily a healthy tank
This catches many beginners.
Water can look perfectly clean while containing harmful concentrations of dissolved waste. You cannot see ammonia or nitrite simply by looking through the glass. Testing matters.
A basic liquid or reliable digital testing system should allow you to keep track of the important parameters relevant to your aquarium. During cycling and the early life of a new aquarium, testing more frequently gives you useful information about how the system is developing.
Eventually, you start learning what “normal” looks like for your aquarium.
Testing doesn't replace observation, and observation doesn't replace testing. They work together.
Don't try to create the perfect aquarium on day one
This might be the advice I most wish new fishkeepers would hear.
Your first aquarium does not need rare plants, expensive equipment, twenty species of fish and an aquascape that looks ready for an international competition.
Start with something manageable.
Learn how your filter behaves. Learn what your tap water is like. Notice where waste collects. Discover how quickly your plants grow. Work out how long routine maintenance actually takes you.
Most of all, get into the habit of watching the animals you keep.
There will be algae at some point. A plant will probably melt. You will buy something you later decide you didn't need. You may stare at a water test and wonder whether that colour is yellow, yellow-green or some previously undiscovered shade created specifically to annoy aquarists.
That's part of learning.
A successful aquarium isn't one in which nothing ever changes. It is one where you understand the system well enough to notice change and respond appropriately.
Take your time, build the aquarium around the needs of its inhabitants, and get the basics right.
The rest becomes much easier.