Coral sand not really any good in respect of hardness,get yourself some Epsom salts(magnesium sulphate) from the chemists and bicarbonate of soda ,get mine from the local spar,and some cichlid lake salts,I use seachem,add the lake salts to your tank water as per dosage,check your pH ,kh,GH and add small doses of the other two until you get those levels up to what your tangs require ,pH 8 plus kh and GH around 16,when you do water changes add the required amount of salts to maintain those readings,your LFS prob doesn't add any salts to their tang tanks the fish just acclimatise to the water they are in,but for them to flourish and hopefully breed it is better to get your tank water similar to their natural environment