I recently bought a 90l tank with 2 angelfish, 2 rosy barbs, 2 small catfish (unsure of name), 2 pink gouramis, 1 golden gourami, 2 other gouramis, 1 huge silver dollar, and a silver shark which recently passed away, im expecting a lot of them to die but they have lived in that tank for years at my friends, im gutted when the fish die so should i expect more to pass away?