There is an ever increasing number of bee nutrition products on the market all reporting to be the best for your hive.
One I have been interested in for a while is adding a seaweed extract to syrup. There is an Irish made product Hive Alive which has various other additives and is very popular.
Also various home brew versions of it.
Agrisea here in NZ have rebranded their Animal tonic and it is used as an additive to syrup. I have used this and saw no negative effects on the bees, in fact they did better in this apiary than another. Too many variables to draw a result based on a singl