I have a single rainbow shark in a 20litre tank how big will it grow and also im getting a 3ft tank in two months after two months if i put my fish in the new tank will it grow still after two months also ive had the fish for one week
I'm not 100% sure of what exactly you're asking, but that is a very small tank for a rainbow shark. Rainbow sharks get a bit over 6", and must have some space. That 3 foot tank should be ok for it, though. It's a persistent myth that fish only grow to the size of their tank, and while fish will stunt in confined conditions, it is not healthy for the fish, and will ultimately kill it if those conditions are not corrected.