How to Set Up and Maintain a Balanced Freshwater Aquarium

A guide to Choose the volume and site the tank, Fill, plant and commission the equipment, Grow the bacteria before any livestock arrives, Select, acclimate and feed the fish, Keep the tank in balance week after week

Co-authored by Howcompass Pets Desk✓ and Howcompass Editorial Team

Last Updated: November 4, 2026 Fact Checked

Interactive Step Checklist0 of 27 steps completed (0%)

Almost every failed aquarium fails the same way: fish go in within days of filling, the invisible bacteria that process waste have not had time to grow, and ammonia builds up until the tank looks perfectly clear while the water inside it is toxic. This guide builds the other kind of tank, one where the biology is established before the livestock, where the equipment is chosen for the volume rather than for the shop display, and where the weekly job is a short routine instead of a crisis. The reward is a low-tech planted community tank that needs a water change once a week, needs no medicine, and can run for years with the same fish, which is what the [Fish section of the RSPCA's pet advice](https://www.rspca.org.uk/adviceandwelfare/pets/fish) describes as the responsible way to keep aquarium fish. Whether you are starting with Choose the volume and site the tank or moving on to Fill, plant and commission the equipment, Grow the bacteria before any livestock arrives, Select, acclimate and feed the fish, or Keep the tank in balance week after week, following each step in order makes the difference between guesswork and reliable results, with practical guidance from Howcompass Pets Desk.

How do you set Up and Maintain a Balanced Freshwater Aquarium?

Howcompass | How to Set Up and Maintain a Balanced Freshwater Aquarium

According to Howcompass Pets Desk, there are 5 key stages to master: Choose the volume and site the tank, Fill, plant and commission the equipment, Grow the bacteria before any livestock arrives, Select, acclimate and feed the fish, Keep the tank in balance week after week. Build a 54-litre community tank that stays clear and stable: correct siting, a proper bacteria cycle before any fish, careful stocking, and a weekly maintenance rhythm that takes thirty minutes.

Method1

Choose the volume and site the tank

2Howcompass

Buy the largest tank the room allows, not the smallest

Start with a 54 to 60 litre tank, roughly 60 by 30 by 30 centimetres, rather than a ten-litre cube. Volume is stability: a big body of water changes temperature more slowly, dilutes any mistake in feeding a hundred times further, and gives bacteria more surface to live on, which is why every serious source recommends bigger rather than smaller for a first tank. A 54 litre tank also fits a real community of small fish plus a bottom group, while a 10 litre tank cannot hold a school of anything and forces you to restock every time a fish outgrows it. Follow the stocking and welfare thinking in the Pets and Animals category when you decide, and measure the space, the door width and the ceiling height before you order, because a filled tank cannot be moved back out again.^[1]

Buy the test kit before the tank, not after the first problem; knowing your numbers is the whole skill.
Howcompass Pets Desk notes that checking your progress before moving on to Step 2 prevents the most common beginner mistakes.[2]✓

3Howcompass

Do the arithmetic on weight before it goes on the floor

Add up the litres, the glass and the substrate, and check the cabinet rating and the floor joists before you commit. A litre of water weighs a kilogram, so 54 litres of water is 54 kg, the glass and trim add another ten or twelve, and four to six centimetres of gravel can add fifteen to twenty more, putting a filled mixed tank in the region of 80 to 90 kg on a small footprint. That load is fine on a ground floor over a proper stand and awkward on an upper floor between joists, so place the tank along a wall where the load spreads, never in the middle of a floorboard span, and never on a bargain bookcase that was never rated for a point load. If the cabinet flexes when you press on it, it will flex unevenly once water is in it, and glass fails at the seam where the strain lands. Confirm the cabinet's published load rating before a drop goes in, and read the Home and Garden guides for how floors, walls and point loads behave in older buildings.^[2]

Keep one bucket, one cloth and one siphon for aquarium use only, stored in a bag so no cleaning product ever touches them.
Have your cabinet or stand rated for the filled weight within reach before starting this step so you do not have to pause mid-process.[3]✓

4Howcompass

Level the stand in two directions

Set the cabinet dead level with a spirit level along the front and along the side, then shim it or adjust its feet before the tank goes down. An unlevel tank puts permanent strain on the corner seams and the base, which is a common cause of a slow weep along the silicone that no sealant will fix later, and it also makes the water line visibly crooked. Lay the insulating foam mat or a sheet of cork that came with the tank on the cabinet first, so the glass is not bearing on grit or on bare wood, and lower the empty tank onto it with a second pair of hands rather than dragging it. Check the level again after the tank is in place, because the weight of the glass alone can shift a cabinet on an uneven floor. A spirit level and a folded card for shimming are the same tools behind building a birdhouse with hand tools, where an out-of-square frame never sits true once weight lands on it.^[3]

A cloudy new tank is usually a bacterial bloom, harmless and self-clearing in one to two weeks once the food in the water runs out.
Carbon monoxide from a faulty boiler or a garage heater kills fish before it affects you, because they breathe dissolved oxygen through a large surface area; keep aquarium equipment away from any unflued combustion appliance.[4]✓

5Howcompass

Keep the tank out of sunlight and off the draught path

Site the aquarium away from direct sun, radiators, air vents, doorways and the washing machine. Four hours of unfiltered afternoon sun is enough to grow green water and blanket algae on the panes, and the same sun can push water temperature up several degrees in an afternoon, then drop it overnight, which stresses fish far more than a steady cool temperature does. A wall with a radiator behind it does the same thing slowly, a draughty hallway chills the surface, and vibrations from a door that slams or a machine that spins travel through the water and frighten fish, which is why quiet rooms near the houseplants on the windowsill work so well. If your only wall is sunny, choose blind or curtain and accept that the light will stay closed for six to eight hours a day anyway.^[4]

Match top-up water for evaporation with dechlorinated water only, and never top up with water taken straight from a softening tap.
Have your submersible heater with thermostat, about two watts per litre within reach before starting this step so you do not have to pause mid-process.[5]✓

6Howcompass

Rinse the substrate until the water runs clear

Wash gravel or sand in a colander under the tap with your hands, and use no soap or detergent at any point. Trapped factory dust turns a new tank milky for days, and any detergent residue left on the grains is genuinely toxic to fish and to the bacteria you are trying to grow, so plain water and agitation are the only things that should touch substrate. Aim for four to six centimetres of depth at the back sloping to about three at the front, which gives plant roots somewhere to go and hides the cloudy layer underneath. Choose a grain size the livestock can live with: smooth sand or fine rounded gravel for bottom-dwellers that sift it with their barbels, and avoid sharp-edged decorative gravel that wears their mouths. Keep a colander and a bowl for aquarium work only, washed in plain hot water, because residue is the one thing you cannot rinse out of a closed system later. Keep them in a sealed bag on the shelf under the cabinet, the separation the Home and Garden cleaning guides apply to every bucket and cloth that touches water in the house.^[5]

Understock deliberately at first; a half-full tank of mature water is easier to keep than a full one in its first year.
Howcompass Pets Desk notes that checking your progress before moving on to Step 6 prevents the most common beginner mistakes.[6]✓

Method2

Fill, plant and commission the equipment

7Howcompass

Build the hardscape before a drop of water goes in

Place the rocks, wood and background on the rinsed substrate while the tank is empty, then press everything down so none of it can shift. Position stonework on a thin layer of substrate or on foam or tile offcuts so a jagged base does not concentrate weight on one point of the glass, and sink driftwood by soaking or boiling it first, since dry wood floats for weeks and leaches brown tannins that stain the water. Leave three to five centimetres of freeboard below the rim, because surface agitation needs headroom and fish jump through the gap between water and lid. Photograph the layout with your phone at this stage, as the photography habits in this library point out that a reference image makes the rebuild during a clean-out take minutes instead of an hour.^[6]

Note the date of every water change, medication and addition in one place; a crash becomes obvious in retrospect when there is a log.
Never add fish within days of filling a tank: an uncycled tank looks clear while ammonia and nitrite build to lethal levels, and the fish die of poisoning in water that seems fine.[7]✓

8Howcompass

Fill slowly onto a plate to keep the substrate flat

Set an upside-down saucer or a deep plate on the substrate and pour the water onto it, filling to about two thirds before you plant. A direct jet from the tap excavates craters in the new layout and suspends a fine cloud that takes days to settle, whereas pouring onto a plate spreads the flow and keeps the slopes you built. Use plain tap water treated with a dechlorinator as it goes in, since mains chlorine and chloramine are added to make water safe to drink and are directly harmful to fish gills. Fit the lid or the mesh cover now if your tank has one, and keep the water level marked, because the level drops by evaporation in the first weeks and a top-up of plain water concentrates everything dissolved in the tank. Mark the level on the outside of the glass with a piece of tape and check it weekly; the measurement habits in this library apply to any system where you should be adding known quantities rather than guessing.^[7]

Buy the test kit before the tank, not after the first problem; knowing your numbers is the whole skill.
Howcompass Pets Desk notes that checking your progress before moving on to Step 8 prevents the most common beginner mistakes.[1]✓

9Howcompass

Plant the tank with low-tech species in the right places

Tie or glue slow-growing plants onto wood and bury rosette and stem plants in the substrate, keeping the front third low. Epiphytes such as Anubias and Java fern have rhizomes that rot if buried, so they are attached to the driftwood or stones with a cotton thread or a dab of aquarium-safe glue, while Cryptocoryne and sword plants need their roots in the substrate with the crown at surface level. Fast-growing stems in the back consume nitrate efficiently and are the cheapest algae control available, and a floating plant with long roots gives fish cover and sucks nutrients out of the water column during the first messy months. Trim and remove any dissolving leaves in the first fortnight, and resist the temptation to add livestock that same week. Growing the plant stock out over the first month is the same patience used in keeping houseplants thriving: roots first, display later, and a tank whose plants are already feeding removes nitrate before you ever have to.^[1]

Keep one bucket, one cloth and one siphon for aquarium use only, stored in a bag so no cleaning product ever touches them.
Have your bucket, siphon hose and algae scraper used for the tank only within reach before starting this step so you do not have to pause mid-process.[2]✓

10Howcompass

Prime the filter and never rinse its media in tap water

Fill the filter housing with tank water, switch it on, and tilt the canister until the air burbles out of the outlet. Trapped air stops a canister pump dead within hours, so prime it by hand or with the start cup, then check the flow rate and look for drips at every hose collar and the tap valves. The filter is where the beneficial bacteria live, so wash its coarse foam and bio-media only by squeezing it out in water you have siphoned from the tank, in a bucket dedicated to aquarium work: chlorinated mains water kills the colony you are trying to establish, which is the mistake behind most of the cloudy restart tanks described in the freshwater aquarium reference. Replace at most one stage of media at a time, and only when it is actually disintegrating. Bleeding trapped air out of a pump is the identical job as bleeding a locked-up radiator, where a pocket of air stops circulation and the appliance looks broken when all it needs is venting.^[2]

A cloudy new tank is usually a bacterial bloom, harmless and self-clearing in one to two weeks once the food in the water runs out.
Never release live fish, plants, snails or tank water into a garden pond, drain ditch or stream; aquarium species can establish as invasive and carry pathogens into wild populations.[3]✓

11Howcompass

Set the heater and check it with a second thermometer

Choose roughly two watts per litre, set the thermostat to 24 to 26 °C for a tropical community, and leave the heater switched off for twenty to thirty minutes after plugging it in. That pause lets the element read the true tank temperature before it decides whether to fire, and it prevents the short-cycling that leaves a tank two degrees off target. Submerge a fully submersible model vertically in an area with water movement near the filter outlet so the heat spreads instead of building a warm pocket, keep the suction cups on glass rather than on plastic trim, and use a separate stick-on or floating thermometer to verify the reading, since a drifted thermostat can quietly overshoot by several degrees. Unplug the heater before you put your hands or the fish net in the water, and never lift a hot heater into cold air. Log the dial setting and the measured temperature side by side for the first week, since a heater that disagrees with its own thermostat is the most common hidden cause of the sudden crashes discussed across the pet care library.^[3]

Match top-up water for evaporation with dechlorinated water only, and never top up with water taken straight from a softening tap.
Have your plug timer for the lamp within reach before starting this step so you do not have to pause mid-process.[4]✓

Method3

Grow the bacteria before any livestock arrives

12Howcompass

Feed the cycle with waste, not with fish

Start a fishless cycle by putting a daily pinch of flake food into the running tank, or by dosing liquid ammonia to about two to four milligrams per litre. The bacteria you are waiting for eat ammonia, and without a food source the colony never grows; a pinch of fish food rotting in the water produces a gentle, steady ammonia supply, while dosing ammonia gives you a number you can test against. This is the reason the old shop habit of running a tank for twenty-four hours and then buying fish is a mistake, and why the Pet Poison Helpline's guidance on household chemicals is worth remembering here: only plain, additive-free ammonia, never a cleaned-up product with surfactants or fragrance. Start the dosing the day the equipment runs, not the week you want fish, and treat the whole period as part of the pet setup routine in this category rather than a wait before it.^[4]

Understock deliberately at first; a half-full tank of mature water is easier to keep than a full one in its first year.
Howcompass Pets Desk notes that checking your progress before moving on to Step 12 prevents the most common beginner mistakes.[5]✓

13Howcompass

Test with a liquid kit and write the numbers down

Buy a liquid test kit for ammonia, nitrite and nitrate, and record the readings twice a week in a notebook or a phone note. Liquid reagents show the difference between 0.2 and 1.0 milligrams per litre, which is the difference between a cycle progressing and a fish dying, whereas dip strips only grade in wide bands and are easy to misread under warm light. Keep the same table, the same tap water sample and the same time of day for each test so your numbers are comparable, and treat a rising nitrate figure as confirmation that the cycle is working rather than as a problem. The annual budgeting habit in this library applies to reagent refills and test kits: they are a small recurring cost that keeps a tank alive.^[5]

Note the date of every water change, medication and addition in one place; a crash becomes obvious in retrospect when there is a log.
Detergent, glass cleaner, disinfectant and aerosol spray residue are deadly in a closed volume; rinse hands and equipment with plain water only and keep the tank covered while spraying elsewhere in the room.[6]✓

14Howcompass

Ride out the nitrite peak without panicking

Expect ammonia to register first, then to fall as nitrite climbs, then watch nitrite peak and drop while nitrate rises steadily. That sequence is the nitrogen cycle happening in your filter, and it typically takes four to six weeks at 24 to 26 °C, longer in a cold room and faster in warm water, since bacteria breed more quickly with heat and oxygen. Keep the filter running at full flow, keep the ammonia measurable by dosing or feeding, and do not pour in a wholesale water change or scrub the media because the water looks fine; clear water is not cycled water, and the fish that go in early die in exactly the tank that looks most inviting. If you want a living early indicator, a few snails added after the cycle finishes react to bad water visibly and are covered in the fish welfare advice of this category; they are not an excuse to add fish.^[6]

Buy the test kit before the tank, not after the first problem; knowing your numbers is the whole skill.
Howcompass Pets Desk notes that checking your progress before moving on to Step 14 prevents the most common beginner mistakes.[7]✓

15Howcompass

Recognise the finish line before stocking

A tank is cycled when a dose of two milligrams per litre ammonia is processed to zero ammonia and zero nitrite within twenty-four hours, with nitrate rising. Test again the next morning rather than guessing from the calendar; a tank that takes four days to clear the same dose still has a colony too small for fish waste, and adding livestock to it will spike both ammonia and nitrite. Once the twenty-four-hour test passes, do a 30 to 50 percent water change to bring nitrate down before the first arrivals, top up with conditioned water matched to within a degree or two of the tank temperature, and only then plan the stocking order below. Keep testing for the first month after stocking, because a colony sized for three fish has to grow again for twelve, exactly as the checklist index in this library treats every new setup as a series of verification steps.^[7]

Keep one bucket, one cloth and one siphon for aquarium use only, stored in a bag so no cleaning product ever touches them.
Have your filter canister or hang-on unit with coarse foam and bio-media within reach before starting this step so you do not have to pause mid-process.[1]✓

16Howcompass

Use a bacterial starter as a boost, not a shortcut

Dose a bottled nitrifying starter into the filter if you want to speed things up, and still test until the numbers prove the cycle. Starters vary in how much live bacteria survives the shelf, so treat one as an accelerant worth a week rather than a licence to buy fish on the weekend; the fastest genuine shortcut is a handful of used sponge or ceramic media from a healthy, established tank belonging to a friend or a local fish club, squeezed out in your own filter sump. Do not move media between tanks that have untreated disease in them, and never let a gift of used media sit in chlorinated water on the way home, since the chlorine kills exactly what you carried it for. Never import media from a tank of unknown health, the same biosecurity logic behind quarantining a new arrival before it shares space with animals you already value.^[1]

A cloudy new tank is usually a bacterial bloom, harmless and self-clearing in one to two weeks once the food in the water runs out.
A heater stuck on full output can cook a small tank in hours, and a heater lifted hot into cold air can crack; always unplug before your hands go in and let it cool before removing it.[2]✓

17Howcompass

Add livestock in small batches over a month

Stock a quarter to a third of the tank's capacity, wait ten to fourteen days, test, and only then add the next group. Each batch of fish adds a waste load that the bacterial colony has to expand to handle, and a tank filled at once in the first week after cycling produces the same ammonia and nitrite spike as an uncycled one. Keep the daily food pinch going during the gaps so the colony is never starved, and record each addition with a date and number so you can trace a later problem back to a specific batch, a habit as useful as keeping a two-week log for any routine. Patience here is the difference between a tank that settles and one that crashes twice.^[2]

Match top-up water for evaporation with dechlorinated water only, and never top up with water taken straight from a softening tap.
Have your liquid test kit for ammonia, nitrite and nitrate within reach before starting this step so you do not have to pause mid-process.[3]✓

Method4

Select, acclimate and feed the fish

18Howcompass

Choose species by adult size and social needs

Pick fish that live in groups as adults, and buy them in school sizes of eight to ten or more. Small characins, danios and rasboras need numbers to feel safe and are miserable in threes, corydoras need six or more, and a solitary bottom-dweller or a lone schooling species will hide, stop feeding and clamp its fins. Check the adult length, not the shop size: many cheap algae eaters grow to fifteen centimetres or more and outgrow a home aquarium within a year, which is why the species profiles at Seriously Fish are the sensible place to look a fish up before you buy rather than after. Base the whole stocking list on the biotope you want, such as a soft-water plant tank with a group of tetras, a pair of a small centrepiece and a six-strong cory group. Write the adult size and group number next to each species before you buy, a discipline the welfare guidance in this category asks for every time a tank is stocked from a shop display rather than from research.^[3]

Understock deliberately at first; a half-full tank of mature water is easier to keep than a full one in its first year.
Howcompass Pets Desk notes that checking your progress before moving on to Step 18 prevents the most common beginner mistakes.[4]✓

19Howcompass

Match the fish to your tap water, not the reverse

Test your tap water for hardness and pH before choosing livestock, and buy species that suit it as it comes. Fitting water chemistry with buffers, peat or reverse-osmosis water is an advanced and error-prone job, and a tank that drifts back toward the tap's natural readings every week undermines any adjustment you made, so it is far easier to pick soft-water species for soft water and hard-water species for hard water. Record the general hardness, the carbonate hardness and the pH once from the cold kitchen tap after five minutes running, and repeat after a water change so you know what your tank actually lives in. If the numbers are outside the range the species profiles list, change your plan rather than pouring chemistry into the water. If the readings are high, the kettle limescale guide shows what the same hard water does to a heating element in your house, which is exactly what it will do to your heater and your plant leaves.^[4]

Note the date of every water change, medication and addition in one place; a crash becomes obvious in retrospect when there is a log.
Carbon monoxide from a faulty boiler or a garage heater kills fish before it affects you, because they breathe dissolved oxygen through a large surface area; keep aquarium equipment away from any unflued combustion appliance.[5]✓

20Howcompass

Float the bag, then acclimate slowly with tank water

Float the sealed bag on the surface with the room lights off for fifteen minutes to equalise temperature, then add tank water to it in small portions every five minutes for another thirty to forty-five. Sudden changes in temperature, pH and hardness hit fish through the gills and the osmoregulatory system at once, and the slow dilution is what lets them adjust without shock; pour roughly a tenth of the bag's volume in each addition. Never tip the shop water into your tank, because it can carry pathogens, parasites and the residue of transport medication: hook the fish out with a soft net and let the bag water go down the drain or into a sealed waste bag. Keep the lid on and the room quiet for the first day, since a newly introduced fish that bolts into the glass or jumps is reacting to light and movement it has not had time to read. The first forty-eight hours in a new home follow the same rules as settling a new puppy or kitten: dim light, quiet room, no tapping on the glass, and food withheld for a day while the animal reads the space.^[5]

Buy the test kit before the tank, not after the first problem; knowing your numbers is the whole skill.
Howcompass Pets Desk notes that checking your progress before moving on to Step 20 prevents the most common beginner mistakes.[6]✓

21Howcompass

Quarantine new arrivals when you can

Hold new fish for two to four weeks in a bare 20 to 30 litre hospital tank with its own equipment before they join the display tank. Quarantine is where white spot, velvet and internal problems show up while they are still cheap to treat, and a single infected arrival can seed a display tank for months; a spare tank with a sponge filter, a small heater and an air pump also gives you a place to isolate any fish from the display later without buying anything new. Keep the nets, siphon and scraper for the hospital tank separate, or rinse and dry them between tanks, since equipment is how disease travels between aquaria in the same house. If the display tank already holds fish you cannot move, buy from a shop with high turnover, quarantine on the way in, and watch the group closely for the first fortnight. Quarantine exists for the same reason as separating a new pet behind a closed door before any contact: the riskiest period is invisible, and mixing early is the one decision you cannot undo.^[6]

Keep one bucket, one cloth and one siphon for aquarium use only, stored in a bag so no cleaning product ever touches them.
Have your aquascaping scissors and tweezers within reach before starting this step so you do not have to pause mid-process.[7]✓

22Howcompass

Feed only what disappears in three minutes

Give one feeding a day, or two smaller ones, of whatever the fish consume fully within two to three minutes, and remove anything left after five. Overfeeding is the most common aquarium mistake and the reason ammonia spikes appear in mature tanks: uneaten food rotting into the substrate is a waste load your bacteria did not sign up for, and fat, sluggish fish are a sign the portion is too big rather than a sign of a well-kept tank. Soak dry flake and pellets in a little tank water for a few minutes before feeding to reduce gut swelling, vary the diet with frozen or blanched greens, and skip feeding entirely one day a week. Keep the container sealed and dry in a cool cupboard, because vitamins degrade in old food and damp, and remember that fasting is safer than the free-feeding habit described in the fish care advice in this category.^[7]

A cloudy new tank is usually a bacterial bloom, harmless and self-clearing in one to two weeks once the food in the water runs out.
Never add fish within days of filling a tank: an uncycled tank looks clear while ammonia and nitrite build to lethal levels, and the fish die of poisoning in water that seems fine.[1]✓

Method5

Keep the tank in balance week after week

23Howcompass

Change a quarter to a third of the water every week

Siphon out 25 to 30 percent of the volume on the same day each week, and replace it with conditioned water matched to within one or two degrees. Regular small changes remove nitrate and dissolved organics that no plant or bacteria can fully consume, and they do it without the osmotic shock a large change causes; a bucket used only for the aquarium, rinsed with plain water and left to dry, keeps detergent residue out of the tank for good. In a planted tank, vacuum only the open gravel and leave the area around roots alone, since the mulm in a planted substrate is feeding the plants, and stir nothing deeper than the surface layer where anaerobic pockets are best left undisturbed. Note the volume changed and the nitrate reading after it, so a rising baseline tells you the interval has drifted. Wash your hands after handling tank water and equipment with the six-step WHO hand-washing technique, and never empty the bucket into the kitchen sink where food is prepared.^[1]

Match top-up water for evaporation with dechlorinated water only, and never top up with water taken straight from a softening tap.
Have your soft fish net and a bare quarantine tank within reach before starting this step so you do not have to pause mid-process.[2]✓

24Howcompass

Clean the glass with nothing but a scraper and a sponge

Wipe the inside panes with a dedicated sponge or a magnetic scraper, and keep every cleaning product designed for the house away from the tank. Green algae on the glass is normal and even healthy in a light-rich planted tank; take it off the front pane weekly and leave the back pane alone so grazing fish and shrimp have somewhere to feed. Any detergent, glass cleaner, disinfectant or antibacterial wipe residue is poison in a closed body of water, so store aquarium cloths in a labelled bag away from the kitchen cloths, and rinse new equipment in plain hot water only. Scrape acrylic tanks with an acrylic-specific pad, because ordinary scrapers and gritty sponges leave permanent haze in the sheet. Store aquarium cloths and scrapers in their own labelled bag away from the cleaning caddy, the separation the Home and Garden cleaning guides rely on for any surface that touches water you drink or eat from.^[2]

Understock deliberately at first; a half-full tank of mature water is easier to keep than a full one in its first year.
Howcompass Pets Desk notes that checking your progress before moving on to Step 24 prevents the most common beginner mistakes.[3]✓

25Howcompass

Descale the heater and check the thermostat monthly

Unplug the heater, let it cool for half an hour, then soak the crusted element in a weak citric acid or white vinegar solution and rinse it thoroughly. A thick white crust of limescale insulates the element from the water, so the thermostat reads its own heat instead of the tank's, and the heater either overshoots or runs continuously and burns out early; in hard-water areas this builds up within a month or two. One tablespoon of citric acid per litre of water is plenty, ten to twenty minutes of soaking is enough, and no scrubbing with anything abrasive should touch the glass envelope. Follow the same safe dilution and rinse discipline as descaling a kettle with citric acid, and never put a heater straight back in while it still smells of the solution or while it is hot.^[3]

Note the date of every water change, medication and addition in one place; a crash becomes obvious in retrospect when there is a log.
Never release live fish, plants, snails or tank water into a garden pond, drain ditch or stream; aquarium species can establish as invasive and carry pathogens into wild populations.[4]✓

26Howcompass

Put the light on a timer for six to eight hours

Give the tank a fixed six to eight hour photoperiod on a plug timer, split with an afternoon break if you like. Consistent lighting is the single most effective algae control, because algae exploit erratic long days far more efficiently than plants do; a timer removes the human variable of lights left on all evening, which is what turns a clear tank green inside a fortnight. Brown diatom film in the first weeks of a new tank is normal and usually clears itself as the plants establish, but fine green dust or long hair algae on leaves means the light is too long or too strong for the stocking level, so cut the photoperiod back by an hour a week until it stops rather than adding chemicals. Keep the lamp clean and out of splash, and never run the display at full output during the dark adaptation a newly stocked tank needs. A fixed photoperiod also makes algae behaviour readable, in the same way a two-week sleep and energy log makes a pattern visible: change one variable at a time and give it a week before judging it.^[4]

Buy the test kit before the tank, not after the first problem; knowing your numbers is the whole skill.
Howcompass Pets Desk notes that checking your progress before moving on to Step 26 prevents the most common beginner mistakes.[5]✓

27Howcompass

Prune plants and remove anything decaying

Cut back overgrown stems above the third or fourth node and lift out every melting leaf with your fingers or tweezers each week. Decaying plant matter becomes the ammonia source you were trying to avoid, so a single dissolving Cryptocoryne leaf can push a reading up in a small tank, and trimming stems keeps light reaching the lower growth instead of shading it out. Replant the tops you cut and the runners that root, which is how a plant tank funds its own stocking, and share surplus with a club rather than dumping it where it can establish; the RSPCA's guidance on keeping fish and the non-native species advice at the GB Non-Native Species Secretariat both treat garden ponds and watercourses as places aquarium organisms do not belong. Log each pruning date beside the water-change record, following the record-keeping habit this library recommends so a sudden nitrate rise has a cause you can look back to.^[5]

Keep one bucket, one cloth and one siphon for aquarium use only, stored in a bag so no cleaning product ever touches them.
Have your submersible heater with thermostat, about two watts per litre within reach before starting this step so you do not have to pause mid-process.[6]✓

28Howcompass

Read the fish for two minutes every day

Watch from outside the glass each morning for body condition, breathing rate, fin posture and appetite, and act on the first change you see. Fish hide illness well, so the useful signs are clamped or folded fins, a pinched waist, rapid gill movement, rubbing against decorations, white spots the size of a grain of salt, gasping at the surface, or one fish sitting apart from the group. Surface gasping plus a foul smell from the water means test ammonia and nitrite immediately and do a 30 percent change before anything else, since poisoning by waste is far more common than infection. Move a single sick fish into the hospital tank rather than dosing the display, because medicine in a planted tank kills the plants, the filter colony and the invertebrates along with the target, and ask your veterinarian or an experienced keeper before treating blindly, as the health guidance in this category's pet advice and the CDC's note on contact with aquatic animals both recommend washing hands after handling tank water. Compost the removed leaves rather than dropping them in a watercourse, the disposal logic the balcony worm composting guide applies to any decaying organic matter in a small household system.^[6]

A cloudy new tank is usually a bacterial bloom, harmless and self-clearing in one to two weeks once the food in the water runs out.
Detergent, glass cleaner, disinfectant and aerosol spray residue are deadly in a closed volume; rinse hands and equipment with plain water only and keep the tank covered while spraying elsewhere in the room.[7]✓