Sharks require soft acidic or 'Amazon" water. 

pH: 6.5 - 6.8

GH: 7 - 9

KH: 5 - 6

Silver sharks should be kept in groups of at least two or more and require a large aquarium of at least 120cm.

Sharks like Red Tail, Rainbow or Albino should be kept in groups of two or more and require an aquarium of at least 60cm. They also should have plenty of hide holes or caves on the bottom of the aquarium.