Hi mate it's relatively variable but mid line is about 3.3% salt so 33grams salt for every litre of water, we have a salt water pool and it runs at less 1/5 this still most think it is sea salty.
So anyway anything between 30 and 40g/L will probably see you fine, still it will not properly taste exactly like sea water because there is other stuff in there but it will be just as salty.
cheers fnq