Aquarium guides
Plain-English answers to the questions every fishkeeper asks, from cycling a new tank to a maintenance routine that sticks. For individual species, see the fish care guide. Read how our guides are made.
Getting started
Water quality
- How to cycle an aquarium: the nitrogen cycle, step by stepCycle a new aquarium before adding fish: what the nitrogen cycle is, a fishless cycle step by step, how long it takes and how to tell it is done.
- Aquarium water parameters explainedWhat ammonia, nitrite, nitrate, pH, GH, KH and temperature mean in an aquarium, safe ranges for freshwater fish, and how often to test.
- Fishless cycling: how much ammonia to add and what to testHow much ammonia to add for a fishless cycle, how much to top up, a day-by-day testing log, and how to restart a cycle that has stalled.
- KH vs GH in an aquarium: what's the difference?GH measures calcium and magnesium; KH measures the carbonates that keep pH steady. Units, dGH to ppm, how to change each, and which fish want which.
- How to lower pH in an aquarium (and how to raise it)Lower or raise aquarium pH safely: why steady pH beats a target number, how KH controls it, RO water, natural methods and the trouble with pH chemicals.
Maintenance
- How often should you change aquarium water?How much aquarium water to change and how often, how to do it safely, and how to use your nitrate readings to tell whether your schedule is right.
- Aquarium maintenance checklist: daily, weekly and monthlyA simple aquarium maintenance routine: what to check every day, what to do each week and month, warning signs to watch for, and how to keep track.
- How to clean an aquarium filterWhen and how to clean an aquarium filter without losing your cycle: rinse media in tank water, never replace it all at once, and keep the impeller clean.
- How often should you feed aquarium fish?How often and how much to feed aquarium fish, the signs of overfeeding, how to feed fry, and what to do when you go away on holiday.
Choosing and keeping fish
- How to choose compatible aquarium tank matesFive checks for compatible aquarium fish: water parameters, temperament, adult size, swimming level and group size, with examples from our care guide.
- Neon tetra vs cardinal tetra: which should you choose?Neon tetra vs cardinal tetra side by side: tank size, temperature, pH, hardness, size and care level, and whether the two can share a tank.
- Guppy vs molly: which should you choose?Guppy vs molly compared: tank size, temperature, pH, hardness, adult size and lifespan, whether they can share a tank, and what to know about fry.
- Amano shrimp vs cherry shrimp: which should you choose?Amano shrimp vs cherry shrimp side by side: tank size, temperature, pH, hardness, size, breeding and algae eating, and whether to keep both together.
- Bristlenose pleco vs otocinclus: which should you choose?Bristlenose pleco vs otocinclus compared: tank size, water, adult size, group needs and diet, whether they can share a tank, and the common pleco.
- Ocellaris vs percula clownfish: which should you choose?Ocellaris vs percula clownfish compared: tank size, water, reef safety, lifespan and how to tell them apart, plus why not to mix the two species.
- Corydoras vs kuhli loach: which should you choose?Corydoras vs kuhli loach compared: tank size, water, adult size, group needs and behaviour, and how to keep both together on a soft sand bottom.
Fixing problems
- Cloudy aquarium water: causes by colour and how to clear itWhy aquarium water turns white, green, yellow or brown, which kinds are harmless, and what to do about each, starting with an ammonia and nitrite test.
- Why are my fish gasping at the surface?Fish gasping at the top of the tank: the usual causes (low oxygen, heat, ammonia, nitrite, gill problems), what to do right now and how to prevent it.
- How to lower ammonia in an aquariumHow to bring aquarium ammonia down fast, why the same reading is more dangerous at high pH, where ammonia comes from and how to stop it coming back.
- How to lower nitrate in an aquariumLower aquarium nitrate with water changes, with the dilution maths, then keep it down with plants, lighter feeding, sensible stocking and a tap-water test.
- New tank syndrome: signs, how to fix it and how to prevent itNew tank syndrome is ammonia and nitrite poisoning in an uncycled tank: the signs, how to save your fish with tests and water changes, and how to stop it.
- Why are my fish dying? A step-by-step checklistFish dying and you don't know why? A step-by-step checklist: water tests, recent changes, temperature, new fish, overstocking, bullying and disease signs.
Fishkeeping in India
- How to cool an aquarium in summer in IndiaKeep a fish tank cool in an Indian summer: why heat cuts oxygen and makes ammonia more toxic, cooling methods ranked by cost, and fish that cope with heat.
- Aquarium power cut plan: what to do when the electricity goesWhat fails first when an aquarium loses power, battery and USB air pumps, sizing an inverter or UPS, restarting a filter safely, and feeding during cuts.
- Can you use tap water or borewell water for an aquarium in India?Tap, borewell and RO water for aquariums in India: removing chlorine, what a TDS meter can and can't tell you, GH and KH tests, and nitrate in groundwater.
- Aquarium setup cost in India: what a 2 feet tank costsWhat a 2-foot (54–63 L) aquarium costs to set up and run in India: dated listing prices for the essentials and electricity maths for your own tariff.
- Best fish for a 2 feet tankFish for a 2-foot aquarium: how much water it really holds, three stocking plans with group sizes and shared ranges, and a summer heat check.
- Best aquarium fish for Indian weatherBeginner aquarium fish that cope with India's heat and hard water, chosen from our care data, with honest caveats on tank size, goldfish and native fish.