Well, based on that Patrick it is not 1000 g/l of solution, it is 1000 g / liter of water which will be more than 1 liter and close to 2 Kg in weight. As you say a 50% wt/vol solution. Be careful, this will become very very hot during mixing and may boil over.
I knew that.
Right there is another clue that something was wrong with my Potassium sulphite. I started with hot water and adding the sulphite cooled it considerably. But I was adding 320 grams to 750 ml.