Freshwater aquarium fish

Cycle the tank first: four to six weeks with an ammonia source and no fish, until the test kit reads zero ammonia and zero nitrite. Match the fish to the water you have, because a guppy in soft acidic water and a cardinal tetra in hard alkaline water both fade and sicken. Buy for the adult, because the common pleco in the shop is 2 inches and reaches 15.7 inches (40 cm). And keep schooling fish in schools: six of one species, not one each of six.

1. 01

   Cycle first

   Four to six weeks with no fish, until ammonia and nitrite read zero

2. 02

   Match the water

   Hard and alkaline for livebearers, soft and acidic for tetras

3. 03

   Buy for the adult

   A common pleco is 2 inches in the shop and 15.7 inches grown

4. 04

   Schools are schools

   Six of one species, not one each of six

Hard, alkaline tap water suits the livebearers and the rift lake cichlids: the sailfin molly lists a pH from 7 to 8 and takes brackish water, the electric yellow cichlid a pH from 7.5 to 8.5, and Boeseman's rainbowfish a pH from 7 to 8 at 81–86°F (27–30°C). Soft, acidic water suits the tetras and the fish of the Amazon: the cardinal tetra lists a pH from 5 to 7, and the discus a pH from 6 to 7 at 79–90°F (26–32°C), marked difficult. The cherry barb lists a pH from 6 to 8 and lives in either.

The common pleco reaches 15.7 inches (40 cm) and lists 85 gallons (320 liters). The oscar is marked aggressive at 13.8 inches (35 cm) for 95 gallons (360 liters). The silver arowana reaches 39.4 inches (100 cm) and lists 396 gallons (1,500 liters). The redtail catfish reaches the same length and lists 1,506 gallons (5,700 liters). The iridescent shark is sold as a 3 inch schooling fish and reaches 39.4 inches (100 cm) for 528 gallons (2,000 liters). The clown loach is the one most people keep, and it reaches 11.8 inches (30 cm) for 75 gallons (285 liters). All of them are sold small.

The betta is marked beginner at 3 inches (7.5 cm) for 7 gallons (25 liters), and it is marked aggressive and solitary, so it is kept alone or with calm fish that stay out of its way. The angelfish is marked easy at 5.9 inches (15 cm) for 30 gallons (115 liters). The pearl gourami is 4.7 inches (12 cm) for 30 gallons (115 liters), marked easy and peaceful. The kribensis is a 3.9 inch (10 cm) cichlid for 20 gallons (75 liters) that pairs and breeds in a cave. The Bolivian ram is the calm dwarf cichlid at 3.1 inches (8 cm), marked peaceful. The honey gourami is 2 inches (5 cm) for 20 gallons (75 liters), marked easy and peaceful.

The bronze cory is marked easy at 3 inches (7.5 cm) for 20 gallons (75 liters) and shoals in a group of six. The peppered cory is 2.8 inches (7 cm) for 21 gallons (80 liters) at 72–79°F (22–26°C), and Sterba's cory is 2.6 inches (6.5 cm) for the warm end at 75–82°F (24–28°C). The kuhli loach is a 3.9 inch (10 cm) eel-shaped fish marked easy that comes out at night. The bristlenose pleco grazes algae at 4.9 inches (12.5 cm) for 20 gallons (75 liters). The otocinclus is 2 inches (5 cm) for the same tank, marked medium because a new tank has nothing for it to eat.