Bring water and salt to the boil, add fish and simmer for 5 minutes. Remove fish, cool, then flake off flesh with your hands and set aside. Return heads and bones to the water. Add tamarind water and simmer for a further 10 minutes, then strain through a fine sieve and set stock aside.
Pound or blend lemongrass, turmeric, belacan, chilli and galangal to a paste. Add to fish stock with s