[header] How to breed and care for platies [title] If you are setting up a new tank, get a filter, a heater and some stones. [title] Determine how many platies you want or can fit in your tank without over crowding the tank. [step] The general rule is 1 inch (2.5 cm) of fish per gallon of tank water. 
Size your tank based on the adult size of the fish, not their current size. Platies get up to 2 inches (5.1 cm) long as adults.