Aquarium fish care comes down to five things done consistently: a tank sized for the adult fish, a cycled filter, stable water chemistry, a measured feeding routine, and tank mates that tolerate each other. Get those right and most disease, algae and aggression problems never start.
This page is the index to every FishCare AI care guide. Species guides come first — pick your fish and you get tank size, temperature, diet, tank mates and the problems that species is prone to. Below that, guides are grouped by the job you are doing: setting up a tank, testing water, clearing algae, choosing substrate or handling an emergency. At the end you will find the baseline numbers, the weekly routine and the answers that apply to almost every aquarium.
Aquarium fish care in short
Cycle the tank before adding fish. Keep ammonia and nitrite at 0 ppm and nitrate under 40 ppm. Change 20–25% of the water weekly with dechlorinated, temperature-matched water. Feed once or twice a day, only what the fish finish in about two minutes. Match temperature, pH and hardness to the species you keep, and add new fish a few at a time.
Aquarium Fish Care Guides by Species
Each guide covers minimum tank size, temperature and water parameters, diet, adult size, temperament and the health problems that species runs into most often.
Freshwater fish
Melanotaenia · schools of 6+ · 30–55+ gal · hard water
20+ gallons · sand substrate · group of 6+
5+ gallons heated · 78–80°F · gentle flow
10+ gallons · 74–82°F · beginner livebearer
20+ gallons · 65–75°F · heavy waste load
20+ gallons · 75–82°F · hard water
10+ gallons · 70–82°F · easy livebearer
20+ gallons long · 72–82°F · fry care
10+ gallons · 72–78°F · school of 6+
15+ gallons · 75–82°F · soft water
10+ gallons · 64–77°F · very hardy
20+ gallons · 68–77°F · cooler clean water
10+ gallons · nano shoal of 8+
20+ gallons · sand substrate · peaceful
20+ gallons mature · biofilm grazer
size varies by species · heavy filtration
30+ gallons · wood and caves required
29+ gallons tall · 76–82°F · pairs bond
55+ gallons · 82–88°F · advanced
75+ gallons · heavy filtration · messy
20+ gallons · 80–84°F · soft water
125+ gallons · shoal of 4+ · fast swimmer
pond-only · seasonal feeding · high oxygen
blood parrot cichlid · 30+ gal · sinking food
species-first · teeth care · live and frozen food
tight lid · air access · check local legality
protect the eyes · smooth decor · sinking food
Saltwater fish
predator · 100–300 gal · meaty frozen food · eats small tank mates
surgeonfish · 75–180+ gal · nori daily · ich-prone
20+ gallons marine · captive-bred · hardy
125+ gallons · advanced marine · ich-prone
75+ gallons · algae-based diet · grazer
10–30+ gallons · covered tank · sand bed
20+ gallons · peaceful · jumps without a lid
Shrimp, snails and amphibians
5–10+ gallons mature · stable water · no copper
10+ gallons mature · best algae grazer
5–10+ gallons · calcium · will not breed in freshwater
10+ gallons · calcium and blanched vegetables
fully aquatic · shallow water · slow feeder
20+ gallons · 60–64°F · species-only tank
Species deep dives
Aquarium Care Guides by Category
Once you know your species, these guides cover the work itself — setting the tank up, keeping the water right, feeding, and fixing the things that go wrong.
Getting started
Tank setup, cycling, feeding, cleaning and first fish choices.
Step-by-step from empty glass to a cycled, stocked aquarium.
Hardy species that forgive the mistakes every new keeper makes.
Compare tank size, temperature, feeding and difficulty side by side.
The test kit, dechlorinator, siphon and spares to keep on hand.
Simple daily jobs a child can own, and what an adult must handle.
Acclimating shop-bought fish and what the care label leaves out.
Water quality and testing
Safe pH, ammonia, nitrite, nitrate, hardness and temperature, with fixes.
Sources, preparation, the nitrogen cycle and water change routines.
Tap, well, RO and distilled compared, with treatment steps.
Dechlorinating, temperature matching and remineralising before a change.
Feeding and plants
Portion size and frequency by species, tank size and stocking.
Light, substrate, fertiliser and trimming for live plants.
Beginner plant species, placement and how plants consume nitrate.
Algae control
which algae eaters work · by tank size · what eats which algae
The 7-step plan: light, nutrients, water changes, flow, plants, eaters, then drops.
Identify BBA, kill it with peroxide, fix the CO2 and flow behind it.
Spot a true SAE, and why the chinese algae eater is not one.
Balance light, nutrients and plants without harming the fish.
Flow rate by tank size, media order, cleaning, and low flow as an algae cause.
Substrate, decoration and hardscape
Choosing, soaking, sinking and cleaning wood safely.
Grain size, depth and why bottom-dwellers need it.
When gravel beats sand, and how to vacuum it properly.
Marine biological filtration and reef structure basics.
Aragonite grain choice, depth and sand-sifting livestock.
Work out how many pounds of sand or gravel your tank needs.
Emergencies and problem solving
Power cuts, gasping fish and how to restore dissolved oxygen fast.
Safer bowl care as a stopgap, and the better long-term setup.
Ich, fin rot, dropsy, velvet and other conditions by species.
Enter your test results and see which readings need action.
Planning tools and calculators
- Tank size calculator
- Aquarium planner
- Fish compatibility checker
- Equipment calculator
- Aquarium volume calculator
- Betta water parameters
- Tank size calculators by species
- Koi pond calculator
- All aquarium tools
Fish identification
Not sure what species you have? Start with a photo, or work through the trait charts on our fish identification site.
Aquarium Fish Care Basics
These are the numbers and habits that sit underneath every species guide above. If a fish is unwell, check this list before you reach for medication — water quality explains most sudden problems.
The five things every aquarium needs
- Enough water volume. Size the tank to the adult fish, not the juvenile in the shop. A larger volume dilutes waste and resists temperature swings, which is why a 20-gallon tank is easier to keep alive than a 5-gallon one.
- A cycled filter. Beneficial bacteria convert ammonia to nitrite and nitrite to nitrate. Until that colony exists, every meal you feed becomes a toxin. Cycle before stocking, and never wash media in tap water.
- Stable water chemistry. Fish tolerate a wide range of values but not rapid change. A pH of 7.6 held steady beats a "perfect" 7.0 that swings half a point a day.
- Controlled feeding. Two small meals beat one large one. Uneaten food is the main source of nitrate, and nitrate is what feeds algae.
- Compatible stocking. Match temperature ranges, temperament and adult size. Most aggression problems are stocking problems that were decided at the shop.
Water parameters at a glance
| Parameter | Target (freshwater community) | Act when |
|---|---|---|
| Ammonia (NH₃) | 0 ppm | Any reading above 0 — water change now |
| Nitrite (NO₂⁻) | 0 ppm | Any reading above 0 — cycle is incomplete |
| Nitrate (NO₃⁻) | Under 40 ppm; under 20 ppm preferred | Above 40 ppm — larger or more frequent changes |
| pH | 6.5–7.8, stable | Swings of more than ~0.3 in a day |
| Temperature | 74–80°F / 23–27°C tropical | Drifts of more than 2°F, or a failed heater |
| KH (carbonate hardness) | 3–8 dKH | Below 3 dKH — pH can crash overnight |
| GH (general hardness) | 4–12 dGH | Below 8 dGH for livebearers; above 8 dGH for soft-water species |
| Chlorine / chloramine | 0 | Any untreated tap water entering the tank |
Cold-water, brackish and marine tanks differ. Goldfish and koi want 65–75°F, discus want 82–88°F, and marine tanks add salinity (1.023–1.025 specific gravity) and alkalinity to the list. Always follow the individual species guide over a general table.
A weekly and monthly care routine
| How often | What to do |
|---|---|
| Daily | Feed once or twice, only what is eaten in about two minutes. Count the fish. Check the heater reading. Look for gasping, clamped fins, hiding or white spots. |
| Weekly | Test ammonia, nitrite and nitrate. Change 20–25% of the water with dechlorinated, temperature-matched water. Vacuum roughly a third of the substrate. Wipe the front glass. |
| Monthly | Rinse filter media in old tank water — never tap. Trim plants. Check the impeller, tubing and airline. Top off evaporation with fresh dechlorinated or RO water, not saltwater. |
| Quarterly | Replace worn media (not all at once). Check test kit expiry dates. Deep-clean the substrate in sections across several weeks. Reassess stocking as fish grow. |
Six mistakes that cause most beginner losses
- Adding fish on day one. With no bacterial colony, ammonia climbs within 48 hours and burns gills. Cycle first, or stock very lightly and test daily.
- Buying by shop size. A two-inch common pleco reaches 18 inches. A bala shark needs 125 gallons. Check adult size before you buy.
- Overfeeding. The most common single cause of nitrate build-up, algae blooms and cloudy water in a new tank.
- Cleaning too hard. Replacing all the water and scrubbing the filter in the same session removes the bacteria and restarts the cycle.
- Medicating before testing. Most "sick fish" cases are ammonia, nitrite or temperature. Test first; medication on top of bad water makes things worse.
- Mixing incompatible fish. Goldfish with tropicals, bettas with fin-nippers, or a single schooling fish kept alone all end badly. Use the compatibility checker before you stock.
Aquarium Fish Care FAQ
What is aquarium fish care?
Aquarium fish care is the routine of keeping a tank's water, filtration, temperature, feeding and stocking within the range your species tolerate. In practice it means a cycled filter, ammonia and nitrite at 0 ppm, nitrate under 40 ppm, a stable temperature, a measured feeding schedule and tank mates that suit each other.
How often should I change aquarium water?
For most stocked freshwater community tanks, change 20–25% of the water once a week using dechlorinated water matched to tank temperature. Heavily stocked tanks, goldfish and large cichlids often need 30–50% weekly. Never change all the water at once, and never rinse filter media in tap water.
How much should I feed aquarium fish?
Feed once or twice a day and offer only what the fish finish in about two minutes. Uneaten food breaks down into ammonia and then nitrate, which is the most common cause of algae and poor water quality in new tanks. One fasting day a week is fine for most adult community fish.
What water parameters do aquarium fish need?
Ammonia 0 ppm, nitrite 0 ppm, nitrate under 40 ppm (under 20 ppm preferred), pH stable between roughly 6.5 and 7.8, KH 3–8 dKH so the pH does not crash, GH 4–12 dGH, and 74–80°F (23–27°C) for a tropical community tank. Stability matters more than hitting an exact number.
Do I need to cycle a new aquarium before adding fish?
Yes. A new filter has no bacteria to convert ammonia into nitrite and then nitrate, so fish added on day one are exposed to ammonia burn. A fishless cycle takes about four to six weeks, or a few days to two weeks if you seed the filter with mature media from an established tank. The cycle is finished when ammonia and nitrite both read 0 ppm within 24 hours of dosing ammonia.
What is the easiest fish to care for in an aquarium?
Guppies, platies, zebra danios, neon tetras and corydoras are the usual beginner picks: they tolerate a wide temperature range, accept prepared foods and stay small enough for a 10–20 gallon tank. Bettas are easy too, provided the tank is heated and filtered rather than an unheated bowl.
How do I know if my aquarium fish is sick?
Watch for clamped fins, gasping at the surface, hiding, loss of appetite, white spots, cotton-like growths, red streaks or rapid gill movement. Test the water before reaching for medication — ammonia, nitrite or a temperature swing explains most sudden illness, and correcting water quality resolves it without treatment.
What size aquarium should a beginner start with?
A 20-gallon tank is easier to keep stable than a 5 or 10 gallon, because a larger water volume dilutes ammonia spikes and temperature swings. Choose the tank around the adult size of the fish you want, not the size they are in the shop.