3,895 answers about fish & aquatics
A healthy aquarium is a balanced one — water chemistry, filtration, stocking and feeding all work together, and most fish problems start with the water. This page gathers the fish and aquatics library of KinsLe Answers in one place, organized by topic for freshwater and saltwater keepers alike. Every answer is original, written by KinsLe, and tied to a real KinsLe feature.
562 answers in Choosing & Adopting — page 15 of 24
Cherry shrimp have low monthly running costs once their tank is set up. A small planted tank of five to ten gallons uses little electricity, the shrimp eat tiny amounts of shrimp food supplemented by the biofilm and algae already in the tank, and the main recurring buys are water conditioner, occasional mineral-rich…
A bristlenose pleco is inexpensive to feed but not free to run: it needs a heated, filtered tank of at least 20 to 30 gallons, and its heavy waste output means bigger, more frequent water changes, so water conditioner and electricity are the steady costs. Food itself is cheap — algae wafers plus blanched zucchini,…
A betta has low monthly keeping costs, because the whole setup is small: a heated five-to-ten-gallon tank uses little electricity compared with a big community aquarium. The regular costs are a good pellet or flake food — one small container lasts a long time — water conditioner for the weekly partial change, and…
Angelfish sit in the middle of the freshwater cost range, and most of the monthly spend is really the cost of their tank: a heated, filtered 29-to-55-gallon setup runs a heater, filter and lights every day, and that electricity is the steadiest driver. After that comes food — angelfish do best on a quality staple plus…
In a 40-gallon you can keep a proper show school of fifteen to twenty zebra danios, and at that size the group tightens up, sweeps down the tank together, and shows the behaviour people buy danios for. The tank's length matters more than its depth, so a 40-gallon breeder or long layout beats a tall one. There is also…
Ten to twelve zebra danios make a full, active school for a 20-gallon, and the longer footprint of a 20-gallon long suits their racing style better than a tall tank of the same volume. If the danios will share the tank with other fish, drop the school to eight and spend the remaining room on tankmates that use…
A school of six zebra danios is the right number for a 10-gallon — six is the minimum group size these social fish need to behave naturally, and a standard 10-gallon gives them just enough length for their constant, fast swimming. Choose the longest 10-gallon footprint you can, keep a tight-fitting lid because danios…
A 40-gallon comfortably holds twenty-five to thirty-five adult guppies, and it gives a breeding colony real breathing room compared with smaller tanks. Start with fifteen or so healthy adults — males to females at about one to two — and let the colony grow into the space rather than filling it on day one. Dense…
Plan on roughly ten to fifteen adult guppies in a 20-gallon, and start below that number because guppies breed their own replacements. A good opening stock is two or three males with about twice as many females — females outnumbering males spreads the males' constant attention — plus plants and cover where fry can…
Two fancy goldfish fit a 40-gallon comfortably, and three is the realistic ceiling if filtration is oversized and water changes never slip. The working guide is about twenty gallons for the first fancy and ten for each additional fish, and a 40-gallon breeder's wide footprint gives fancies — most of which stay in the…
One — if it is a fancy goldfish. A 20-gallon can house a single fancy variety such as a fantail or oranda for life, provided filtration is strong and water changes are regular, but it has no room for a second goldfish: the usual guide is twenty gallons for the first fancy and ten more for each one after. Single-tailed…
Honestly, none — not as a permanent home. Even the smallest fancy goldfish grows to six or eight inches, produces heavy waste, and needs around twenty gallons for a single fish, while single-tailed commons and comets grow past a foot and belong in ponds or very large tanks. A ten-gallon can hold a baby fancy for a few…
A few at a time: three to five small fish is a sensible first addition to a cycled new tank, then wait at least a week or two before adding more. A new filter's bacteria colony is only big enough to handle the waste it has already been fed, so each small group lets the colony grow to match before the next one arrives.…
A 40-gallon can hold a proper school of twelve to fifteen corydoras, and this is where the fish really reward you: a large group forages, rests and darts about as one body in a way a bare-minimum group never does. You can keep one generous school of a single species, or two species in groups of at least six each if…
Eight to ten is a comfortable school for a 20-gallon, since six is the minimum for corydoras to behave naturally and 20 gallons gives a group of the common bronze, peppered or panda corydoras the floor space to spread out and forage together. Stick to one species rather than mixing two half-groups, because corydoras…
About six, and only of a dwarf species, because corydoras are schooling fish that need their own kind around them and a 10-gallon suits a group of six pygmy or habrosus corydoras, which stay around an inch long. The familiar bronze and peppered corydoras grow far bigger and belong in a 20-gallon or more, where a group…
One male, again — even 40 gallons will not make two male bettas tolerate each other, because each claims the whole tank as his territory rather than a corner of it. What the extra volume genuinely buys is a richer single-betta community: a school of small, peaceful fish, bottom dwellers, and dense planting with room…
Still one male, because twenty gallons does not change betta nature and two males in any home tank will find each other and fight. What 20 gallons does open up is a choice: one male as the centrepiece of a calm community, or a sorority of females, meaning a group of at least five females in a heavily planted tank,…
One — a 10-gallon keeps a single betta, male or female, and the number does not rise the way it does for schooling fish. Two males will fight until one is badly hurt, and a male-and-female pairing is only brought together briefly for breeding by experienced keepers. The good news is that one betta in 10 gallons is a…
A 40-gallon comfortably holds a bonded pair of angelfish, or a group of four to five young angelfish while you wait for a pair to form. Forty gallons gives each fish room to claim a corner, which is what keeps the peace; in smaller volumes the same group turns on its weakest member. A practical plan: buy five…
One angelfish is the comfortable answer for a 20-gallon, or a bonded pair if the tank is a tall model and the two fish are already a proven pair. Two angelfish bought at random are not a pair, and unbonded adults in 20 gallons often end with one bullying the other into a corner. A practical approach: keep a single…
None — a 10-gallon tank is too small for even one angelfish. The young angelfish in the shop looks tiny, but it grows into a fish about six inches long and far taller through the fins, and a 10-gallon gives it neither the swimming room nor the water volume its waste needs. The practical move is to enjoy the 10-gallon…
Your tank is overstocked when the water tells you before the fish do: ammonia or nitrite shows up on tests, nitrate climbs again within days of a water change, and you are changing water just to keep readings safe. The fish add their own evidence, gasping at the surface, squabbling constantly, and youngsters that stop…
Pick fish that are active, bright-eyed and swimming steadily in the middle of the tank, with fins held open rather than clamped and no spots, patches or torn edges. Skip any fish from a tank that holds a dead or gasping tankmate, and watch the fish eat if you can, because healthy stock rushes food. One practical…
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