Nano Fish FAQ

10 gallons is the realistic minimum for a nano tank, 20 gallons long is the sweet spot for stability. Anything under 10 gallons is fragile — parameter swings happen fast, bioload tolerance is small, and you are limited to a handful of species. A 20 gallon long gives you room for a proper school of small fish plus a cleanup crew, and it costs only marginally more than a 5 gallon to set up.

Only for tropical species. Cold-water nano fish like White Cloud Mountain Minnows, Bitterling, and Rainbow Shiners thrive at room temperature (16–22°C) with no heater. Tropical species like guppies, tetras, and bettas need 24–28°C and a heater is non-negotiable. Match the fish to your room or commit to the heater — do not split the difference.

Budget $200–400 for a complete 20 gallon setup: tank ($40), filter ($30), heater ($25), light ($40), substrate ($20), conditioner and test kit ($40), fish ($50–100), plants and decor ($30). You can do it cheaper by buying used, but skimping on the test kit or the conditioner is a false economy — both are essential and both are cheap.

4 to 6 weeks for fishless cycling with pure ammonia, 6 to 8 weeks for fish-in cycling with hardy starter fish. You can shortcut to 2 weeks by seeding with filter media from an established tank. Never add fish to a tank that shows any ammonia or nitrite on a liquid test kit — the cycle is not done.

White Cloud Mountain Minnows (cold-water), Zebra Danios, Cherry Barbs, Ember Tetras, guppies, and Cherry shrimp. All are hardy, peaceful, accept prepared food, and tolerate beginner mistakes. Stay away from discus, German blue rams, Apistogramma, and pea puffers until you have kept a tank successfully for a year.

Goldfish in a nano tank (they get 30 cm), Oscars, common plecos (they get 45 cm), pea puffers in pairs (they fight), male bettas with other male bettas, and any "feeder" fish from the store feeder tank. Also avoid any fish sold without a scientific name — if the store cannot tell you what it is, you cannot care for it correctly.

Yes, as long as you dechlorinate it first with a conditioner like Seachem Prime. Test your tap water for pH, GH, and KH before buying fish, then pick species that match your tap rather than fighting your water. RO water is only needed for sensitive species or if your tap is extremely hard or contaminated.

Yes, always. The only exception is a heavily planted Walstad-method tank with very low stocking, and even then a small sponge filter helps. Filters host the nitrifying bacteria that convert toxic ammonia into less-toxic nitrate — without one, fish waste accumulates and kills fish within days.

Sand for corydoras and bottom-sifting fish (non-negotiable — gravel damages their barbels). Smooth gravel or sand for community tanks. Aquasoil (ADA Amazonia, Fluval Stratum) for planted tanks — it buffers pH down and feeds plant roots. Pool filter sand is the budget choice at $8 for 50 lb.

Start with one hardy school of 6–8 small fish after the tank is fully cycled — Zebra Danios or White Clouds are classic starters. Add a second group 2 weeks later if parameters stay at 0 ammonia and 0 nitrite. Resist the urge to stock the whole tank on day one — the biofilter needs to catch up to each bioload increase.

Cycling is the process of building up nitrifying bacteria in your filter that convert toxic ammonia (from fish waste) into nitrite, then into less-toxic nitrate. The cycle takes 4–8 weeks from scratch. Without it, fish die of ammonia poisoning within days. Cycling is the single most important thing to understand as a new fishkeeper.

25 to 30 percent weekly for most nano tanks. Smaller tanks (under 10 gallons) often need 30 to 50 percent weekly because parameters swing faster. Match temperature and dechlorinate the new water before adding it. Consistent weekly changes are better than occasional large ones.

24–26°C for most tropical community fish, 26–28°C for discus and rams, 22–26°C for corydoras and most tetras, 16–22°C for cold-water nano fish. Pick the fish that match your target temperature rather than mixing species with incompatible needs — you cannot split the difference without stressing something.

6.5–7.5 covers 90% of nano fish. Test your tap water, then pick species that match it. South American dwarf cichlids want 5.5–7.0, African cichlids want 7.8–8.5, most community fish want 6.5–7.5. A stable pH matters more than the exact number — swings kill fish.

GH (general hardness) measures calcium and magnesium — the minerals shrimp need for their shells. KH (carbonate hardness) measures the water's ability to resist pH changes — the buffer. Test both with API liquid kits. Most nano fish tolerate a wide range; shrimp are pickier about GH.

API Freshwater Master Test Kit — the liquid version, not strips. Strips are inaccurate and give false readings at the levels that matter. The master kit costs $35 and does 800 tests. Test ammonia, nitrite, nitrate, and pH weekly for the first 3 months, then monthly once the tank is stable.

TDS (total dissolved solids) is the sum of everything dissolved in your water — minerals, salts, organics. It matters most for shrimp keepers, who target 100–200 ppm for Caridina and 150–250 ppm for Neocaridina. A $15 TDS pen is the cheapest meaningful test in shrimp keeping.

Tap water (dechlorinated) is fine for 90% of nano fish. RO (reverse osmosis) water is needed only for sensitive species (discus, Caridina shrimp, wild-caught Apistogramma) or if your tap is extremely hard or contaminated. Mixing RO with tap to hit a target GH/KH is the standard approach for sensitive species.

What the fish can consume in 2 to 3 minutes, once or twice a day. Fish will eat themselves sick if you let them — underfeeding is always safer than overfeeding. Uneaten food rots and spikes ammonia. A healthy fish is slightly plump; a fat fish is overfed. Skip a feeding day once a week for adult fish.

Once or twice daily for adults. Once a day is plenty for most nano fish. Fry need 4–6 small feedings a day. Adult fish can go 7–10 days without food — you do not need an auto feeder for a week-long vacation, despite what the pet store tells you.

A quality flake or pellet as the staple (Omega One, New Life Spectrum, Fluval Bug Bites), supplemented 2–3 times a week with frozen bloodworm, brine shrimp, or daphnia. Variety is the key — no single food is complete. Soak dry food in tank water for 2 minutes before feeding so it sinks properly.

Yes. Fish will eat until their digestive tract is damaged. The classic case is a betta fed floating pellets — they gulp air with the food, bloat, and develop swim bladder issues. Feed small amounts, remove uneaten food after 3 minutes, and fast one day a week. A fat fish is a sick fish.

Healthy adult fish are fine without food for 7–10 days. Do not use the "vacation feeder blocks" sold at pet stores — they dissolve unevenly and pollute the water. For trips longer than 10 days, use an auto feeder or have someone feed every 4–5 days, pre-measured in a pill organiser so they cannot overfeed.

For routine daily feeding, yes — they remove the temptation to overfeed and they are consistent. For vacations, test the feeder for a week before you leave so you know it actually drops food. Cheap auto feeders are unreliable; the Eheim Everyday and the Fluval.feed are the two I trust.

The old rule of 1 inch of adult fish per gallon is a rough ceiling for nano tanks, 1 inch per 2 gallons is safer for beginners. A 20 gallon holds about 20 inches of fish total — say a school of 10 small tetras plus 6 corydoras. Bioload matters more than length; a 10 cm pleco is not the same as 10 cm of tetras.

Peaceful community fish that share temperature and pH requirements. Tetras, rasboras, corydoras, small plecos, and peaceful barbs are the building blocks. Avoid mixing aggressive species (cichlids, barbs) with long-finned species (bettas, guppies). Check temperature, pH, temperament, and adult size before combining any two species.

One male betta per tank — they will fight to the death. Female bettas can be kept in "sororities" of 5+ in a 20 gallon long or larger, but sororities are advanced and unstable. Skip betta sororities until you have kept bettas successfully for a year. A single male betta in a 10 gallon is the better choice for almost everyone.

Yes, with small-mouthed fish (tetras, rasboras, danios, corys). Avoid shrimp with goldfish, cichlids, gouramis, and bettas — they will hunt adult shrimp. Even small fish eat shrimplets, so provide moss and hiding spots. A cherry shrimp colony in a community tank needs to be self-sustaining — expect losses but not extinction if the tank is planted.

6 minimum for schooling species, 8–10 better. Tetras are schooling fish — a group of 3 is 3 stressed fish. A school of 10 Neon Tetras in a 20 gallon is one of the most rewarding nano setups. Different tetra species do not school together; get 6+ of one species, not 2 each of three species.

Corydoras (6+ of one species, sand substrate) or kuhli loaches (6+ of one species, sand substrate). Pygmy corys work in a 10 gallon; standard corys need a 20 long. Avoid common plecos (too big) and most synodontis (too aggressive). Bristlenose plecos work in a 20 gallon but add real bioload.

Yes. Schooling fish kept solo or in groups of 2–3 are stressed, hide constantly, lose colour, and die young. Six is the minimum, eight to ten is better. Mixed-species schools do not count — the fish know their own kind and do not bond with lookalikes. If you cannot afford 6 of a species, pick a different species.

Overstocking is more bioload than the filter and water-change schedule can handle. Symptoms: detectable ammonia or nitrite, constant nitrate above 40 ppm, fish gasping at the surface, frequent disease outbreaks. Long-term it stunts growth, shortens lifespan, and eventually crashes the tank. Test water — if ammonia or nitrite is detectable, you are overstocked.

Clamped fins (held tight against the body), refusing food, heavy breathing, hiding constantly, white spots or cotton-like patches, ragged fins, abnormal swimming (vertical, looping, on the side). Healthy fish swim normally, eat aggressively, and have erect fins. Any deviation lasting more than 24 hours is a problem.

Raise the temperature to 30°C slowly over 24 hours, treat the whole tank with malachite green (Ich-X) or copper-based medication, and continue for 7–10 days after the last spot disappears. Ich has a life cycle — you have to treat long enough to kill the free-swimming stage or it comes back. Treat the whole tank, not just the affected fish.

Fin rot is a bacterial infection that eats away at the fins — ragged, receding edges, sometimes red or white. The cause is almost always poor water quality. Fix the water (large water changes, gravel vac, check filter) and the early stages resolve on their own. Severe cases need an antibiotic like Kanaplex.

Dropsy is a bacterial kidney infection that causes fluid retention — the fish's scales stick out like a pinecone, the belly swells. By the time you see pineconing, the internal damage is severe and the fish is usually not saveable. Isolate, treat with Kanaplex in food (not just water), and add Epsom salt (1 tbsp per 5 gal) to reduce swelling.

A fish that cannot maintain its orientation — floating to the surface, sinking to the bottom, or swimming sideways. Often caused by overfeeding or constipation pressing on the swim bladder. Fast the fish for 2 days, then feed a cooked peeled pea. If it does not resolve in 5 days, water quality or bacterial infection is the likely cause.

When the fish cannot swim, cannot eat, or is in obvious prolonged distress with no realistic chance of recovery. The humane method is clove oil: add a few drops to a container of tank water with the fish, slowly increase the dose over 15–20 minutes until the fish stops gill movement, then add vodka or more clove oil to ensure death.

Test the water immediately for ammonia, nitrite, and nitrate. The most common cause of sudden death in nano tanks is an ammonia spike from overfeeding, an overcleaned filter, or a dead fish you did not notice. Do a 50% water change with dechlorinated water and figure out the cause before adding any new fish.

Yes. A 2 to 4 week quarantine in a separate 10 gallon tank catches diseases, parasites, and behavioural issues before they reach your display tank. Without quarantine, a single sick fish from the store can wipe out an established community. The quarantine setup costs about $60 and pays for itself the first time it saves a tank.

Condition the breeders with live or frozen food for a week, then trigger spawning with a cool water change (4–5°C cooler than the tank). Egg scatterers (tetras, rasboras) need fine-leaved plants or a spawning mop; remove parents after spawning. Livebearers (guppies, endlers) just need a male and females — they handle the rest.

Fish that release eggs into the water column rather than guarding them — tetras, rasboras, danios, barbs. They scatter eggs over plants or substrate, then eat them if given the chance. To breed, use a spawning mop or fine-leaved plant, remove parents immediately after spawning, and raise the fry separately.

Guppies, endlers, platys, and mollies give birth to live young. Keep 1 male per 2–3 females (otherwise the male harasses a single female to death). The female is pregnant for 4–6 weeks, then drops 20–50 fry. Remove the pregnant female to a breeding box or separate tank before she drops, or the fry get eaten.

Infusoria for the first week (or commercial liquid fry food), then newly hatched brine shrimp or microworms for weeks 2–4, then crushed flake food. Feed 4–6 small meals a day. The first week is the hardest — fry are too small for most food and water quality has to be perfect. Most home breeding attempts fail at the fry stage.

For egg scatterers (tetras, danios, barbs) — yes, immediately. They will eat eggs and fry. For livebearers — yes, the female will eat her own fry. For cichlids (rams, apistogramma, kribensis) — no, they guard the eggs and fry. For corydoras — remove the eggs to a hatching container, leave the parents.

Sponge filter for breeding and shrimp tanks (gentle, no fry getting sucked in), hang-on-back for community tanks (good mechanical filtration, easy to maintain), canister for 40 gallon and up (high capacity, quiet). For a 10 to 20 gallon nano, a sponge filter or a small HOB rated for the tank size is the right choice.

Eheim Jager or Fluval E series — both are reliable, fully submersible, and have a thermostat accurate to 1°C. Size at 5 watts per gallon (so a 20 gallon needs a 100W heater). Avoid cheap no-name heaters — a stuck-on heater will cook your tank and a stuck-off one will chill it. The heater is not the place to save $15.

Nicrew or Finnex Stingray for low-tech tanks ($30–50), Fluval Plant 3.0 or Chihiros WRGB II for high-tech planted tanks ($150–250). For a fish-only tank, any basic LED works. For plants, you need PAR (photosynthetically active radiation) — cheap LEDs do not have enough. Read the planted tank guide before buying a light.

Sand for corydoras (non-negotiable). CaribSea Eco-Complete or ADA Amazonia for planted tanks (buffers pH, feeds roots). Pool filter sand ($8 for 50 lb) for budget. Gravel for community tanks if you do not have bottom-sifting fish. Avoid painted gravel — the paint flakes off and the fish eat it.

API Freshwater Master Test Kit — liquid, not strips. It tests pH, ammonia, nitrite, and nitrate, costs $35, and does 800 tests. Add the API GH/KH kit ($10) if you keep shrimp. Avoid test strips — they are inaccurate at the levels that matter and give false confidence. The Salifert kits are more accurate for advanced keepers but overkill for beginners.